WO2018203297A1

WO2018203297A1 - Ocular misalignment

Info

Publication number: WO2018203297A1
Application number: PCT/IB2018/053120
Authority: WO
Inventors: Dan Oz; Michael Belkin; Ran Yam; Oren Yehezkel; Ruth CASPI
Original assignee: Novasight Ltd
Current assignee: Novasight Ltd
Priority date: 2017-05-04
Filing date: 2018-05-04
Publication date: 2018-11-08
Anticipated expiration: 2019-11-04

Abstract

Disclosed are methods and devices useful for determining the presence and / or the magnitude of ocular misalignment, for example, due to tropia or heterophoria. Some embodiments of the disclosed methods and devices include sequentially displaying multiple different image pairs to a subject, each image pair comprising a left eye image and a right eye image, the display of an image pair comprising concurrently: on a left display surface, displaying a left eye image of the image pair with a left fixation figure for viewing by the left eye of the subject, wherein the left fixation figure is not viewable by the right eye, and on a right display surface, displaying a right eye image of the image pair with a right fixation figure for viewing by the right eye of the subject, wherein the right fixation figure is not viewable by the left eye.

Description

OCULAR MISALIGNMENT

RELATED APPLICATION

The present application gains priority from US Provisional Patent Application No. US 62/501, 124 filed 4 May 2017, which is included by reference as if fully set-forth herein. The present application is also related PCT patent application PCT/IL2016/050232 published as WO 2016/139662, which is included by reference as if fully set-forth herein.

FIELD AND BACKGROUND OF THE INVENTION

The invention, in some embodiments, relates to the field of ophthalmology and, more particularly but not exclusively, to methods and devices useful for determining the presence and / or the magnitude and/or direction of ocular misalignment, for example, due to heterotropia or heterophoria.

The line of vision (also called gaze direction) of a human eye is determined by the visual axis of the eye, an imaginary line that passes through an object being viewed and through the pupil and the fovea of the eye.

When a human without ocular misalignment looks at an object with both eyes, the two eyes are both directed and fixate on the same viewed object so that the respective visual axes of the two eyes intersect at the viewed object. Normally in healthy people when there is no ocular misalignment, the visual system receives two similar but non-identical images, one from each eye, and combines these to form a single stereoscopic image. The situation where the visual axes of both eyes are fixate on the same object and the brain perceives a single stereoscopic image is called binocular fusion. When the person changes the directions of gaze to look at a different object, the two eyes are coupled to move together in a coordinated fashion in the general direction of the different object, but each eye may need to independently make fine fixation movements (called fusional vergence) to fixate on the different object, for example, to fixate on a nearer object.

Orthophoria

Normally for people who are able to align their eyes under binocular viewing, when binocular fusion is suspended (e.g., one eye is covered for a time in excess of ~6 seconds), the eyes are dissociated so that the covered eye tends to move to its rest position while the other eye remains fixed on the viewed object. Orthophoria refers to a normal healthy situation where inducing eye dissociation and suspending binocular fusion, for example when only one eye receives visual stimulus due to occlusion of the other eye, the visual axis of the other (covered) eye remains directed towards the object showing no deviation.

Heterophoria (latent strabismus / latent eye deviation)

Heterophoria (also called latent strabismus or latent eye deviation) refers to a condition of ocular misalignment in the absence of binocular fusion.

One aspect of heterophoria is a condition where the rest position of one or both eyes is not straight ahead.

Another aspect of heterophoria is a condition where in the absence of binocular fusion and visual stimulus to one eye, e.g., one eye is covered and the other views an object, the visual axis of the one (covered) eye is misaligned and therefore not directed towards the same object.

In heterophoria, the latent misalignment is overcome by fusional vergence: in the presence of visual stimulus for both eyes, the sensory and motor system orients the visual axes of the two eyes so that intersection of the visual axes of the two eyes is achieved and both eyes are able to fixate together on the same object. Orthotropia

Orthotropia refers to the normal healthy situation where when both eyes are open and fixated on the same object simultaneously, binocular fusion achieved. In some instances, a person is orthotropic and has latent heterophoria.

Tropia

Tropia, also called manifest ocular deviation, strabismus or "crossed-eyes", is best defined as a condition, in which when viewing an object only one of the eyes is directed at the object of interest, as opposed to normal vision, wherein both eyes are directed on the same object. In some instances, latent heterophoria become tropia for example after extensive visual effort.

Manifest ocular misalignment may lead to diplopia (double vision) that prevents the visual system to achieve binocular fusion. In cases of misalignment and diplopia during childhood, mainly during the critical period of the visual system development, suppression of the deviating eye might be developed leading to a condition named amblyopia) When a person has tropia, the non-deviating eye becomes the leading (non-deviating) eye and the other the deviating eye. An object looked at by the person is the object through which the visual axis of the non-deviating eye passes. The visual axis of the deviating eye deviates from intersection with the non-deviating eye visual axis at the object to some degree.

In some instances, the deviating eye moves in a coordinated fashion with the non- deviating eye under conditions that ordinarily lead to fused image of the two eyes, to direct the deviating eye visual axis in the general direction of the object fixated by the non- deviating eye, but the deviating eye does not fixate on the object.

In the case of eye manifest deviation, where the deviating eye is sufficiently functional so, when the non-deviating eye is covered, the deviating eye is able to fixate independently on an object in order to see it. For children, if no treatment is undertaken, the deviating eye functionality degenerates and amblyopia might develop.

It is therefore important to diagnose the presence of heterophoria and heterotropia at the earliest possible stage, allowing treatment to prevent the development of amblyopia and to prevent vision functionality degradation of the deviating eye and the binocular vision. No less important, it is useful to monitor a person diagnosed as having tropia and/or heterophoria to see whether or not the ocular deviation gets worse with time. In cases where corrective eyeglasses are prescribed for a person suffering from tropia or heterophoria (to improve quality of life and to prevent visual degeneration of the deviating eye), it is critical to have an accurate measure of the deviation magnitude to know whether or not it can be compensated by corrective eyeglasses. In cases where surgical correction of tropia is performed, preoperative evaluation of the magnitude of ocular misalignment is critical as it used for the operation decisions. Cover test

The gold standard method for measuring eye deviation is the Cover Test. The Unilateral Cover Test (UCT) is used to detect the presence or absent of manifest eye deviation (tropia). Unilateral Prism Cover Test (UPCT) is used when tropia is present, for measuring the manifest component of the deviation, whereas the Alternate Prism Cover Test (APCT) is used for measuring the combined manifest (when exists) and the latent deviation or only the latent in the lack of tropia.

A typical cover test is described with reference to the flow chart of Figure 1A.

In 10, a subject looks at an object with both eyes being open for a few seconds. If the subject is orthophoric, orthotropic or suffers only from latent heterophoria, both eyes are fixated on the object. If the subject suffers from tropia, the non-deviating eye is fixated on the object while the deviating eye is not.

In 12, a first eye of the subject is covered with an occluder (e.g., a cover, typically a paddle). While the first eye is covered, the uncovered second eye is observed for any movement, i.e., a change in gaze direction (the direction of the visual axis) of the second eye. No movement of the uncovered second eye indicates that the second eye was already fixated on the object. Movement of the uncovered second eye indicates that, now that the dominant fixating first eye is covered, the deviating second eye wasn't fixating on the object during the binocular viewing.

In 14, the two eyes are uncovered, the second eye is again observed for any movement, i.e., change in gaze direction of the second eye. Movement of the second eye indicates that now that the dominant fixating first eye is uncovered and fixated on the object, the deviating second eye no longer fixates on the object and the visual axis of the deviating eye now deviates from the object.

The covering and uncovering of the first eye and observation of the uncovered second eye is preferably repeated a number of times to confirm an observation of movement or lack thereof of the second eye, and typically also repeated a number of times with the object at near and far distances from the subject, 16.

The cover test is then typically repeated where the second eye is covered / uncovered while the first eye is observed for any change in gaze direction, as described above.

An eye that does not move when the other eye is covered / uncovered is considered a non-deviating eye, 18.

If neither eye moves, i.e., exhibits change in gaze direction when the other eye is uncovered after being covered, the subject is confirmed as being orthotropic with no tropia.

If an eye is observed to move, that is to say, exhibits a change in gaze direction when the other eye is uncovered and covered, the subject is diagnosed as suffering from tropia where the eye that does not exhibit a change in direction of the visual axis is the non- deviating eye and the eye that does exhibit a change in direction of the visual axis is the deviating eye 20 (also called non-fixating eye).

An additional case of deviation is alternate tropia in which the deviating eye can be either of the two eyes alternately, when covering the momentarily non-deviating eye and removing the occlusion the former deviating eye becomes the non-deviating eye.

The direction towards which the deviating eye is directed under binocular conditions determines the type of optical misalignment: exotropia (outwardly away from the point of fixation of the non-deviating eye), esotropia (inwardly away from the point of fixation of the non-deviating), hypertropia (upwards) and hypotropia (downwards). There can be horizontal and vertical deviation present at the same time. Simultaneous prism cover test

In some cases where there is a small manifest deviation (up to 8 prism Diopters) and the visual system adjusts by eccentric fixation. When eccentric fixation is present, monocular fixation of the amblyopic eye does not occur along the foveal visual axis but is eccentric to it, depending on the strabismus type. The eccentric area of fixation is at the angle of strabismus and it is fixed so that no movement of the eyes occurs with the cover test, even though a manifest deviation is present. The magnitude of ocular deviation of the deviating eye of a heterotropic subject suffering from eccentric fixation tropia is determined using a simultaneous cover test where the visual axis of the deviating eye is directed through different prisms, while simultaneously covering the non-deviating eye. Each different prism refracts light with a different magnitude and/or direction. The purpose of the simultaneous prism cover test is for an object viewed by a non-deviating eye under binocular conditions, find a prism that refracts light from the object to align with the foveal visual axis of the deviating eye. As a result, the non-deviating eye and the deviating eye both fovealy fixate on the same object. This allows determination of the magnitude and direction of the manifest ocular deviation.

Unilateral cover test / cover uncover test

The unilateral cover test is performed to determine whether or not a subject suffers from heterophoria.

The Unilateral Prism Cover Test is performed by using an opaque or translucent

(fogged) occluder that is applied to one of the eyes. The occluder is simply held in front of the eye for a few seconds and then removed. If a tropia is present in the non-occluded eye, the examiner will observe the contralateral eye move in order to achieve a fixation when the fixing eye is occluded. Thus, an eye movement on the unilateral cover test indicates the presence of manifest strabismus. It may be necessary to use both horizontally and vertically placed prisms during the test.

The unilateral test is performed substantially as described for the cover test above, except that when a covered eye is uncovered, that eye is observed for any movement. Specifically, a subject looks at an object with both eyes for a time sufficient to achieve binocular alignment, typically a few seconds.

A first eye of the subject is covered with an occluder for approximately 1 or 2 seconds. While covered, the first covered eye is observed for movement. No movement of the covered first eye indicates that the direction of the eye corresponding to binocular fusion is retained even in the absence of visual stimulus, meaning that the person is orthophoric. Movement of the covered first eye indicates that absent visual stimulus and fusional vergence, the first eye moves to a rest position indicating latent heterophoria.

Subsequently, the first eye is uncovered and observed for movement. No movement of the uncovered first eye confirms that binocular fusion was retained in the absence of visual stimulus. Movement of the now uncovered first eye indicates refixation of the first eye on the object, confirming the indication of latent heterophoria.

Alternate cover test

The Alternate Prism Cover Test (APCT) is used for measuring the combined manifest

(when exists) and the latent deviation. In cases where manifest eye deviation, tropia, is not present the APCT measures the latent eye deviation.

During the Alternate Prism Cover Test the examiner occludes one eye and then the other, switching the occluder back and forth between the eyes, without allowing the subject to fuse the eyes between the occlusions. This test measures the total deviation, including the manifest (tropia) and the latent (phoria) components of eye deviation. Next, a prism held over one eye is used to quantify the misalignment. The prism is preferably held in the "frontal plane", so that the rear face of the prism is parallel to the plane of the subject's face. The examiner repeats the test, while holding a prism over the deviating eye until the misalignment is neutralized. The misalignment is quantified based in the magnitude of the prism (measured in Prism Diopters) that is required to neutralize the deviation. It may be necessary to use both horizontally and vertically placed prisms during the test to determine the exact deviation.

After tropia is diagnosed using a unilateral cover test, an alternate cover test is typically performed to determine the full magnitude of the ocular deviation by suspending binocular fusion.

The test typically starts while the subject looks at an object with both eyes open.

One of the eyes of the subject is covered with an occluder for several seconds to suspend binocular fusion, typically not less than 3-5 seconds. The occluder is rapidly moved to alternatingly cover one of the two eyes in a way ensuring that one eye is always covered, the other eye is uncovered, and binocular fusion remains suspended.

When a non-deviating eye is uncovered and a deviating eye is covered, the deviating eye moves to its rest position, even if the subject only suffers from latent heterophoria as there is no binocular fusion.

When a deviating eye is uncovered and a non-deviating eye is covered, the deviating eye re-fixates on the object, the magnitude of the movement indicating the full extent of ocular deviation from the rest position of the deviating eye.

SUMMARY OF THE INVENTION

Some embodiments of the invention herein relate to methods and devices useful for determining the presence and the magnitude and/or direction of ocular misalignment.

According to an aspect of some embodiments of the present invention, there is provided a method for performing an ophthalmic test useful for determining ocular misalignment in a subject having a left eye and a right eye, comprising:

a. sequentially displaying multiple different image pairs to a subject, each image pair comprising a left eye image and a right eye image, the display of an image pair comprising concurrently displaying:

on a left display surface, displaying a left eye image of the image pair with a left fixation figure for viewing by the left eye of the subject, wherein the left fixation figure is not viewable by the right eye, and on a right display surface displaying a right eye image of the image pair with a right fixation figure for viewing by the right eye of the subject, wherein the right fixation figure is not viewable by the left eye;

b. during the sequential display of image pairs, monitoring the gaze direction of at least one of the left eye and of the right eye (preferably both eyes) to determine at least one result from the group of results consisting of:

a gaze direction of a monitored eye in relation to a displayed image pair,

a change in gaze direction of a monitored eye in response to a change in a displayed image pair,

whether or not the gaze direction of a monitored eye is directed at a fixation figure present in a respective the image of a displayed image pair, and whether or not the gaze direction of a monitored eye is not directed at a fixation figure present in a respective the image of a displayed image pair; and

c. from the at least one determined result providing evidence for at least one condition selected from the group consisting of: a presence or an absence of ocular misalignment of the subject (e.g., associated with phoria and/or tropia), a direction of ocular misalignment of the subject (e.g., associated with phoria), a magnitude of ocular misalignment of the subject (e.g., associated with phoria), which eye of the subject is a non-deviating eye, which eye (if any) of the subject is a deviating eye (e.g., associated with tropia), a direction of deviation of a deviating eye of the subject (e.g., associated with tropia). and a magnitude of deviation of a deviating eye of the subject (e.g., associated with tropia).

In some embodiments, the method further comprises: during the sequential displaying of multiple different image pairs, displaying at least one single-fixation image pair comprising a left eye image and a right eye image, wherein: a first image of the single- fixation image pair includes a single fixation figure; and a second image of the single-fixation image pair is devoid of any fixation figure. In some such embodiments, the method further comprises: monitoring the gaze direction of at least one of the left eye and of the right eye to determine at least one result from the group of results consisting of: the gaze direction of a monitored eye when the second image (of the single-fixation image pair) devoid of any fixation figure is displayed; and the gaze direction of a monitored eye when a displayed second image (of a single-fixation image pair) devoid of any fixation figure is replaced with a succeeding image (of a different image pair) including a fixation figure. In some such embodiments, a monitored eye is the eye to which the second image devoid of any fixation figure is displayed. In some such embodiments, a monitored eye is the eye to which the first image (of an image pair) having a single fixation figure is displayed.

In some embodiments, during the sequential display of the image pairs, the left display surface and the right display surface are attached to the head of the subject, thereby having a fixed orientation and distance relative to the head of the subject.

In some embodiments, during the sequential display of the image pairs, the head of the subject can move relative to the left display surface and the right display surface. In some such embodiments, the method further comprises: during the sequential display of the image pairs, determining an orientation of the head of the subject relative to the display surfaces; and based one the determined orientation at least one of:

rejecting a determined result (e.g., the orientation of the head to the display surface indicated that any result is irrelevant, such as the subject shifted their head dramatically); associating a determined result with another determined result (e.g., grouping together results that were determined with the same or similar orientation of the head ); and

modifying a determined gaze direction (e.g., correcting a magnitude of deviation for a change in orientation of the head).

In some embodiments, wherein the subject has at least one non-deviating eye and a second eye, the method further comprises: performing the ophthalmic test at least twice, in a first performance of the test, on the display surface viewed by the non-deviating eye, displaying a fixation figure in a first location of the display surface, and

in a second performance of the test, on the display surface viewed by the non- deviating eye, displaying a fixation figure in a second location of the display surface different from the first location, so that the orientation of the non-deviating eye relative to the head in the first performance of the test is different from the orientation of the non-deviating eye relative to the head in the second performance of the test; and

comparing the evidence provided by the first performance of the test and by the second performance of the test to determine whether a condition is dependent on the orientation of the non-deviating eye to the head. Such embodiments are useful for identifying a subject who suffers from tropia or phoria which manifestation or magnitude is dependent on the gaze direction of the non-deviating eye relative to the skull.

In some embodiments, the method further comprises:

performing the ophthalmic test at least twice, wherein the orientation of the head to the body of the subject in a first performance of the ophthalmic test is different from the orientation of the head to the body of the subject in a second performance of the ophthalmic test; and. comparing the evidence provided by the first performance of the test and by the second performance to determine whether a condition is dependent on the orientation of the head to the body. Such embodiments are useful for identifying a subject who suffers from tropia or phoria which manifestation or magnitude is dependent on the orientation of the head to the body.

According to an aspect of some embodiments of the present invention, there is also provided a method (hereinbelow referred to as a modified unilateral cover test) for finding evidence to determine the presence of ocular misalignment attributable to tropia in a subject having a first eye and a second eye, comprising:

a. concurrently:

on a first display surface, displaying a first image with a first fixation figure for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye, and on a second display surface, displaying a second image with a second fixation figure for viewing with the second eye, wherein the second fixation figure is not viewable by the first eye, wherein the location of the first fixation figure and the second fixation figure on the respective display surfaces is the same;

b. subsequent to 'a', while monitoring the second eye for refixation motion: preventing the first eye from seeing any fixation figure, and on the second display surface, displaying an image with a fixation figure for viewing with the second eye;

c. subsequent to 'b', while monitoring the second eye for motion attributable to loss of fixation:

on the first display surface, displaying a first image with a first fixation figure for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye, and on the second display surface, displaying a second image with a second fixation figure for viewing with the second eye, wherein the second fixation figure is not viewable by the first eye, wherein the location of the first fixation figure and the second fixation figure on the respective display surfaces is the same;

d. accepting as evidence that the second eye is a non-deviating eye if no movement of the second eye is observed in 'b' and/or 'c'; and

accepting as evidence that the subject has tropia and the second eye is a deviating eye if movement of the second eye is observed in 'b' and/or 'c'.

In some embodiments of the modified unilateral cover test, the location of the first fixation figure on the first display surface in 'a' and in 'c' is the same.

According to an aspect of some embodiments of the present invention, there is also provided a method (hereinbelow referred to as a modified unilateral cover test) for determining the magnitude and/or direction of ocular misalignment attributable to tropia in a subject having a first non-deviating eye and a second deviating eye, comprising:

a. concurrently:

on a first display surface, displaying a first image with a first fixation figure for viewing with the first non-deviating eye, wherein the first fixation figure is not viewable by the second deviating eye, and on a second display surface, displaying a second image with a second fixation figure for viewing with the second deviating eye, wherein the second fixation figure is not viewable by the first non-deviating eye, wherein the location of the first fixation figure and the second fixation figure on the respective display surfaces is different; b. subsequent to 'a', while monitoring the second deviating eye for refixation motion: preventing the first non-deviating eye from seeing any fixation figure, and on the second display surface, displaying an image with a fixation figure for viewing with the second deviating eye;

c. subsequent to 'b', while monitoring the second deviating eye for motion attributable to loss of fixation:

on the first display surface, displaying a first image with a first fixation figure for viewing with the first non-deviating eye, wherein the first fixation figure is not viewable by the second deviating eye, and on the second display surface, displaying a second image with a second fixation figure for viewing with the second deviating eye, wherein the second fixation figure is not viewable by the first non-deviating eye, wherein the location of the first fixation figure and the second fixation figure on the respective display surfaces is different; and

d. accepting as evidence that the difference between the location of the first fixation figure on the first display surface and the location of the second fixation figure on the second display surface in 'b' is indicative of the magnitude and direction of ocular misalignment attributable to tropia if no movement of the second eye is observed in 'b' and/or 'c'; wherein the location of the first fixation figure on the first display surface in 'a' and in 'c' is the same.

In some such embodiments the method further comprises:

if the movement of the second eye is observed in 'b' and/or 'c' given a preceding difference between the location of the first fixation figure on the first display surface and the location of the second fixation figure on the second display surface, then repeating 'a', 'b' and 'c' where the difference between the location of the first fixation figure on the first display surface and the location of the second fixation figure on the second display surface is different from the preceding difference.

In some embodiments of the modified unilateral cover test, preventing the first eye from seeing any fixation figure includes: blocking the view of the first eye to the first display surface. In some embodiments of the modified unilateral cover test, preventing the first eye from seeing any fixation figure includes: on the first display surface, displaying an image devoid of any fixation figure.

According to an aspect of some embodiments of the present invention, there is also provided a method (hereinbelow referred to as a modified alternate cover test) for finding evidence of the presence of ocular misalignment attributable to tropia and/or latent heterophoria in a subject having a first eye and a second eye, comprising: a. concurrently:

on a first display surface, displaying a first image with a first fixation figure for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye, and on a second display surface, displaying a second image with a second fixation figure for viewing with the second eye, wherein the second fixation figure is not viewable by the first eye, wherein the locations of the first fixation figure and the second fixation figure on the respective display surfaces are the same;

b. subsequent to 'a',

on the first display surface, displaying a first image with a first fixation figure at a location LI of the first display surface for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye, and preventing the second eye from seeing any fixation figure, for a period of time sufficient to allow the second eye to move to a rest position while the first eye is fixated on the first fixation figure;

c. subsequent to b, while monitoring the second eye for refixation motion:

on the first display surface, displaying the first image of b with the first fixation figure at the location LI of the first display surface for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye, and

on the second display surface, displaying a second image with a second fixation figure at a location of the second display surface for viewing with the second eye, wherein the second fixation figure is not viewable by the first eye,

wherein the locations of the first fixation figure and the second fixation figure on the respective display surfaces are the same;

wherein:

accepting as evidence that the second eye is free of ocular misalignment attributable to tropia and latent heterophoria if no refixation movement of the second eye is observed in 'c', and

accepting as evidence that the second eye has ocular misalignment attributable to latent heterophoria if refixation movement of the second eye is observed in 'c'.

According to an aspect of some embodiments of the present invention, there is also provided a method (hereinbelow also referred to as a modified alternate cover test) for determining the magnitude and/or direction of ocular misalignment attributable to tropia and/or latent heterophoria in a subject having a first eye and a second eye, comprising:

a. concurrently: on a first display surface, displaying a first image with a first fixation figure for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye, and on a second display surface, displaying a second image with a second fixation figure for viewing with the second eye, wherein the second fixation figure is not viewable by the first eye;

b. subsequent to 'a',

on the first display surface, displaying a first image with a first fixation figure at a location LI of the first display surface for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye and preventing the second eye from seeing any fixation figure, for a period of time sufficient to allow the second eye to move to a rest position while the first eye is fixated on the first fixation figure;

c. subsequent to 'b', while monitoring the second eye for refixation motion:

on the first display surface, displaying a first image with a first fixation figure at the location LI of the first display surface for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye, and on the second display surface, displaying a second image with a second fixation figure at a location L2 of the second display surface for viewing with the second eye, wherein the second fixation figure is not viewable by the first eye, wherein the location of the first fixation figure LI and the location of the second fixation figure L2 on the respective display surfaces are not the same;

wherein:

if no refixation movement of the second eye is observed in 'c,' accepting the location of the second fixation figure L2 on the second display surface as indicative of the magnitude and direction of ocular misalignment of the second eye attributable to tropia, latent heterophoria or a combination of tropia and latent heterophoria.

In some preferred embodiments, in 'a', the locations of the first fixation figure and of the second fixation figure on the respective display surfaces are the same.

In some preferred embodiments, the first image displayed in 'c' is the same as the first image displayed in 'b'.

In some embodiments, the method further comprises: if the refixation movement of the second eye is observed in a preceding 'c' with a given location of the second fixation figure L2 on the second display surface, repeating 'b' and 'c' with an updated location L2 of the second fixation figure on the second display surface different from the preceding given location L2. In some embodiments of the modified alternate cover test methods, the first eye is the left eye and the second eye is the right eye. In some embodiments of the modified alternate cover test methods, the first eye is the right eye and the second eye is the left eye. In some embodiments of the modified alternate cover test methods, 'b' and a following 'c' are performed at least two times, one of the two times where the first eye is the left eye and the second eye is the right eye, and the other of the two times where the first eye is the right eye and the second eye is the left eye.

In some embodiments of the modified alternate cover test methods, the period of time in 'b' is not less than 6 seconds.

In some embodiments of the modified alternate cover test methods, preventing the first eye from seeing any fixation figure includes: blocking the view of the first eye to the first display surface.

In some embodiments of the modified alternate cover test methods, the preventing the first eye from seeing any fixation figure includes: on the first display surface, displaying an image devoid of any fixation figure.

In some embodiments of the modified alternate cover test methods, the first and second display surfaces are attached to the head of the subject during performance of the method, thereby having a fixed orientation and distance relative to the head of the subject.

In some embodiments of the modified alternate cover test methods, during performance of the method the head of the subject can move relative to the left display surface and the right display surface, and the orientation of the head of the subject relative to the display surfaces is determined. The results of the method can be modified or interpreted in light of the the determined orientation.

In some embodiments of the modified unilateral cover test or modified alternate cover test methods, the concurrent displaying is simultaneous displaying the first eye image on the first display surface and the second eye image on the second display surface.

In some embodiments of the modified unilateral cover test or modified alternate cover test methods, the concurrent displaying is alternately displaying the first eye image on the first display surface and the second eye image on the second display surface.

In some embodiments of the modified unilateral cover test or modified alternate cover test methods, the first display surface and the second display surface are physically the same display surface. In some embodiments of the modified unilateral cover test or modified alternate cover test methods, the first display surface and the second display surface are physically different display surfaces.

According to an aspect of some embodiments of the present invention, there is also provided a device useful for performing ophthalmic tests, comprising:

a display device comprising a display surface for displaying changeable pairs of images for viewing by a human subject at a distance of at least 30 cm from the subject, each image pair comprising a left eye image and a corresponding right eye image;

an image provider configured to provide image pairs for display by the display device on the display surface; and

an image obstructor wearable by a human subject that, when activated,

allows the left eye of a subject to view left eye image of an image pair displayed on the display surface while preventing the left eye from viewing a fixation figure of a corresponding right eye image displayed on the display surface; and

allows the right eye of a subject to view a right eye image of an image pair displayed on the display surface while preventing the right eye from viewing a fixation figure of a corresponding left eye image displayed on the display surface,

wherein the image provider is configured to provide:

at least one image pair being an identical-location image pair, each image of an identical-location image pair having a single fixation figure where a location of a fixation figure of a left eye image is the same as the location of a fixation figure of a right eye image; and

at least one image pair being a different-location image pair, each image of a different-location image pair having a single fixation figure where a location of a fixation figure of a left eye image is different from the location of a fixation figure of a right eye image.

In some embodiments, the display surface is configured to display the image pairs for viewing by a subject where the image pairs are virtually located at least 30 cm from the subject. In other embodiments, the display surface is configured to display the image pairs for viewing by a subject physically located at least 30 cm from the display surface. In some embodiments, the image provider is configured to provide: at least one image pair wherein one image of the image pair has a single fixation figure and the other image of the image pair is devoid of any fixation figure.

In some embodiments, the display device is configured to simultaneously display a left eye image and a corresponding right eye image of a image pair. In some embodiments, the display device is configured to alternatingly display a left eye image and a corresponding right eye image of an image pair.

In some embodiments, the device further comprises an eye-tracker to identify and report the gaze direction of at least one (preferably both) of the two eyes of a subject looking at the display surface. In preferred embodiments, the eye-tracker reports the gaze-direction to a computerized controller of the device.

In some embodiments, the display device is configured to be attached to the head of a subject so that the display screen is at a fixed physical distance and orientation from the eyes of the subject.

In some embodiments, the display device is configured to display image pairs for viewing by a subject physically located at least 30 cm from the display surface; the image obstructor is physically located between the display surface and the eyes of a subject when worn by a subject being tested with the device; and a left eye image and a right eye image of an image pair are displayed on the same physical display surface.

In some embodiments, the device further comprises an orientation-determiner for determining at least one of: the distance between the head of a subject and the display surface; the roll of the head of a subject relative to the display surface; the pitch of the head of the subject relative to the display surface; the yaw of the head of the subject relative to the display surface; the distance between the image obstructor and the display surface as a measure of the distance between the head of the subject and the display surface; the roll of the image obstructor relative to the display surface as a measure of the roll of the head of a subject relative to the display surface; the pitch of the image obstructor relative to the display surface as a measure of the pitch of the head of a subject relative to the display surface; and the yaw of the image obstructor relative to the display surface as a measure of the yaw of the head of a subject relative to the display surface.

BRIEF DESCRIPTION OF THE FIGURES

Some embodiments of the invention are described herein with reference to the accompanying figures. The description, together with the figures, makes apparent to a person having ordinary skill in the art how some embodiments of the invention may be practiced. The figures are for the purpose of illustrative discussion and no attempt is made to show structural details of an embodiment in more detail than is necessary for a fundamental understanding of the invention. For the sake of clarity, some objects depicted in the figures are not to scale.

In the Figures:

Fig. 1 (prior art) is a flow chart of steps for performing a unilateral cover test;

Fig. 2A is a schematic depiction of a first embodiment of a device according to the teachings herein;

Fig. 2B is a schematic depiction of a second embodiment of a device according to the teachings herein;

Figs. 3A and 3B are flow charts, each describing a different embodiment of a modified unilateral cover test according to the teachings herein; and

Figs. 4A, 4B and 4C are flow charts, each describing a different embodiment of a modified alternate cover test according to the teachings herein.

DESCRIPTION OF SOME EMBODFMENTS OF THE INVENTION

Some embodiments of the invention herein relate to methods and devices useful for determining the presence and the magnitude and direction of ocular misalignment in humans.

In the PCT patent application IL2016/050232 that was published on 9 September

2016 as WO 2016/139662, some of the inventors disclosed, among other disclosures, methods and devices that are useful in the field of ophthalmology.

Herein are disclosed methods and devices that are useful in determining the presence direction and the magnitude of ocular misalignment. The teachings herein may be implemented by a person having ordinary skill in the art without undue or inventive effort upon study of the disclosure herein, especially with reference to methods and devices known in the art of ophthalmology, 3D-cinematography, Virtual Reality (VR) headsets and with reference to PCT patent publication WO 2016/139662. Device according to the teachings herein

According to aspects of some embodiments of the teachings herein, there is provided a device useful for performing ophthalmic tests, e.g., for determining the presence and, in some embodiments the magnitude and direction, of ocular misalignment, (an embodiment of which is device 32 schematically depicted in Figure 2A), comprising: a display device 34 comprising a display surface 36 (in Figure 2A, a XL2411B 3D- ready LED display screen by BenQ, Taipei, Taiwan) for displaying changeable pairs of images for viewing by a human subject 38 at a distance of least 30 cm from subject 38 (physically or virtually), each image pair comprising a left eye image and a corresponding right eye image;

an image provider 40 (in Figure 2A, a Tecra X40-E-BTO laptop computer with 3D graphics card by Toshiba, Minato, Tokyo, Japan) configured by suitable programming and storing suitable data on a hard disk and/or solid-state disk) to provide such image pairs for display by display device 34 on display surface 36;

an image obstructor 42 wearable by a human subject (in Figure 2A, 3D Vision 2

Wireless Glasses by Nvidia Corporation, Santa Clara, CA, USA under control of image provider 40) that, when activated,

allows the left eye of the subject to view a left eye image of an image pair displayed on display surface 36 while preventing the left eye from viewing a corresponding right eye image displayed on display surface 36; and alternatively, allows the right eye of the subject to view a right eye image of an image pair displayed on display surface 36 while preventing the right eye from viewing a corresponding left eye image displayed on display surface 36, wherein the image provider is configured to provide:

at least one image pair that is an identical -location image pair; and

at least one image pair that is a different-location image pair.

Accordingly, the device is configured so that the eyes can concurrently each see an own respective fixation figure but are not able to see the fixation figure of the other eye. In some preferred embodiments, a device according to the teachings herein physically resembles device 32 depicted in Figure 2A, including a display device 34 such as a 3D-ready display screen for displaying changeable pairs of images for viewing by a human subject 38 physically located at least 30 cm from display surface 36 and an image obstructor such as wearable 3D-glasses physically located between the display surface and the eyes of a subject. In such embodiments, the left eye image and right eye image are displayed on the same physical display surface.

In other preferred embodiments, a display device of a device according to the teachings herein is configured to be attached to the head of a subject so that the display screen is at a fixed physical distance and orientation from the eyes of the subject (irrespective of body and head movements of the subject) and the display device is configured for displaying changeable pairs of images for viewing by a human subject virtually located at least 30 cm from display surface, that is to say, the images appear to be at least 30 cm from the human subject. Such virtual location of an image from a human subject is well-known, for example, in the art of virtual reality and can be implemented by a person having ordinary skill in the art upon perusal of the description, for example, using a commercially-available virtual reality headset as both the display device and an image obstructor, where the image obstructor is a function of the construction of the VR headset that prevents a left eye looking at a right-eye image and a right eye from looking at a left-eye image. As known to a person having ordinary skill in the art of VR headsets, in such embodiments the left eye image and right eye image are displayed on physically different display surfaces. Results superior to those achieved using prior art methods can often be achieved when using embodiments where the display device is configured to be attached to the head of a subject so that the display screen is at a fixed physical distance and orientation from the eyes of the subject. Without wishing to be held to any one theory, it is currently believed that the superior results are sometimes achieved because the orientation of the eyes relative to the display surface remains constant throughout the test in terms of at least one of distance, pitch, roll and yaw of the head which, despite the commonly accepted belief, are hypothesized to not be entirely compensated for by the movement of the eyes relative to the head.

As used herein, the term "pitch" of the head relates to the angular orientation of the head in the sagittal plane which is changed by nodding the head, i.e., tilting the head in an arc in the sagittal plane.

As used herein, the term "roll" of the head relates to the angular orientation of the head in the coronal plane which is changed by bobbing the head, i.e., side-to-side tilting of the head in an arc in the coronal plane.

As used herein, the term "yaw" of the head relates to the angular orientation of the head in the transverse plane which is changed by rotating the head, i.e., turning the head left and right in an arc in the transverse plane. Display device and image provider

In device 32 depicted in Figure 2A, display device 34 is a commercially-available 3D- ready LED display screen known in the art of personal and laptop computing. For implementing the teachings herein, any suitable display device that can perform the required functions described herein may be used. In some embodiments, the display device is selected from the group consisting of: a 3D-ready electronic display device with a light-emitting display surface (e.g., plasma screen, LED screen, LCD screen, CRT screen); and a light- reflective display surface.

In device 32 depicted in Figure 2A, image provider 40 is a suitably configured commercially-available general purpose laptop computer including a 3D graphics card. For implementing the teachings herein, any suitable device can be used that can perform the functions required from an image provider as described herein, including being configured to provide the required image pairs for display by the display device.

In some embodiments such as device 32 depicted in Figure 2A, the image provider is a digital laptop computer (e.g., a local general purpose or custom computer, a tablet computer, a remote server, a computer that is an integral part of a VR headset) and the display device is a display screen functionally-associated therewith (e.g., an integral display screen of a computer, an attached display screen, a VR headset). In some embodiments, typically when the display device comprises a projector device with a light-reflective display surface the image provider is a digital computer (e.g., a local general purpose or custom computer, a tablet computer, a remote server) and the display device is a projector device (e.g., XJ-L8300HN by Casio Computer Co, Ltd, Shibuyam Tokyo, Japan) used to project the required images onto a light-reflective display surface (e.g., a projection screen as known in the art of movie theaters and home cinema).

Image Obstructor

In device 32 depicted in Figure 2A, image obstructor 42 is a commercially-available pair of active shutter glasses. For implementing the teachings herein, any suitable image obstructor that can function cooperatively with the display device and the image provider as described herein can be used. The image obstructor is preferably fashioned to allow wearing over a pair of corrective eyeglasses 44. In some embodiments, the image obstructor is a passive device, that is to say, does not require the use of electrical power to operate such as passive 3D glasses known in the art of 3D cinema (e.g., polarized or anaglyph 3D systems). In some embodiments such as device 32 depicted in Figure 2A, the image obstructor is an active device known in the art of 3D cinema, for example, active shutter glasses such as those configured to implement an active shutter 3D system or a virtual reality headset. Image pairs

Image pairs provided by image provider 40 may be any suitable pairs of images, a left eye image and a corresponding right eye image. Although any suitable images may be used, in preferred embodiments the image pairs are digital images.

An image provider is configured to provide at least two different image pairs. By

"different" is meant that at least one of the images of a first image pair is not identical to a corresponding image (left or right) of a second different image pair. That said, in preferred embodiments, an image provider is configured to provide at least 10, at least 20 and even at least 40 different image pairs. In some embodiments, the image pairs are pre-existing stored image data. Alternatively or additionally, in some embodiments, the image provider is configured to generate suitable image pairs.

Fixation figure

At least one image of each image pair includes a single fixation figure. When an image is displayed on the display surface, a fixation figure is a figure apparent in the image that draws the gaze of a observer. Typically a fixation figure of an image according to the teachings herein has angular dimensions that are smaller than the angular dimension of the foveal vision of a subject looking at the image displayed on the display surface and has one or more of shape, counter, resolution brightness, color, shade, contrast relative to the rest of the image that draws the attention and gaze of the human observer.

The size of a fixation figure is preferably relatively small and typically determined based on the distance at which a tested subject is to be located from the display surface, so that an eye viewing the fixation figure will only have one well-defined specified gaze direction. In some embodiments, the largest angular dimension of a fixation figure is not more than 5° as determined from the distance at which a tested subject is to be located from the display surface. In some embodiments, the actual physical size of the fixation figure is adjustable, allowing the size of the fixation figure to be changed whether to match operator preference or to adjust for the distance at which a specific subject is located from the display surface.

The shape of a fixation figure is preferably compact, that is to say, having similar height and width dimensions so that an eye viewing the fixation figure will only have one well-defined specified gaze direction. In some embodiments, the height dimension of a fixation figure is between 30% and 300% of the width dimension. In some embodiments, the height dimension of a fixation figure is between 50% and 200%) of the width dimension. In some embodiments, the height dimension of a fixation figure is between 66% and 150% of the width dimension.

In some preferred embodiments, the size of the fixation figure is selectable, that is to say, an operator can select a size of a displayed fixation figure. For example, in some such embodiments, when a tested subject has low visual acuity the fixation figure is relatively large while when a tested subject has high visual acuity the fixation figure is relatively small.

Number of fixation figures

Each image includes either a single or no fixation figure and at least one image of each image pair includes a single fixation figure. In some image pairs, each one of the two images of the image pair includes a single fixation figure on a fixation-less background (e.g., blank, featureless, or pseudo featureless background which has no features that draw the gaze of a human observer). In some preferred embodiments, the fixation figures of the left image and of the right image of an image pair are not identical. In some preferred embodiments, the fixation figures of the left image and of the right image of an image pair are identical.

In some image pairs as discussed in greater detail hereinbelow, a first of the two images of the image pair includes a single fixation figure on a fixationless background while the second of the two images of the image pair is devoid of any fixation figure.

As noted above, a device according to the teachings herein preferably includes at least one identical -location image pair and at least one different-location image pair.

Identical-location image pairs

In some embodiments, a device includes at least one image pair that is an identical- location image pair. An identical-location image pair is an image pair where each one of the two images of the image pair includes a single fixation figure, where the respective fixation figure is displayed at the same location of the display surface in both the left eye image and the corresponding right eye image. When an identical-location image pair is viewed by a person having orthophoria, the visual axes of both eyes intersect at the fixation figure. In some preferred such embodiments, the image pair is a stereoscopic image pair.

The actual display location of the two fixation figures is any suitable location of the display surface. In preferred embodiments, the display location of the fixation figures on the display surface is operator-selectable, that is to say, the image provider is configured so that an operator is able to select an identical -location image pair where the fixation figures are displayed at a desired display location. In some such embodiments, the image provider is configured to generate an identical -location image pair on receipt of a user-instruction which user instruction includes the desired display location. Additionally or alternatively, in some embodiments the image provider includes multiple pre-existing identical-location image pairs having different display locations, and a user can select a specific identical -location image pair having a desired display location for display.

Different-location image pairs

In some embodiments, a device includes at least one image pair that is a different- location image pair. A different-location image pair is an image pair where each one of the two images of the image pair includes a single fixation figure, wherein:

the fixation figure of the left eye image is displayed at a left figure location of the display surface; and

the fixation figure of the corresponding right eye image is displayed at a right figure location of the display surface, the right figure location being different from the left figure location.

The location difference between the left figure location and the right figure location of a different-location image pair is any suitable difference, for example, the right figure location may be to the left, to the right, above, below or any possible combination thereof of the left figure location. To simultaneously view the fixation figures of a different-location image pair requires that the visual axes of the two eyes do not intersect at either one of the two fixation figures.

In some embodiments, the image provider is configured to provide a different-location image pair where the location difference between the left figure location and the right figure location of a different-location image pair is dependent on input related to a measured of ocular misalignment of a subject.

In some embodiments, the image provider is configured to provide a different-location image pair where the location difference between the left figure location and the right figure location is operator-selectable, that is to say, the image provider is configured so that an operator is able to select a different-location image pair having a desired location difference. In some such embodiments, the image provider is configured to generate a different-location image pair on receipt of a user-instruction which user instruction includes a desired location difference. Additionally or alternatively, in some embodiments the image provider includes multiple pre-existing different-location image pairs and a user can select a specific different- location image pair having a desired location difference for display.

The actual locations of the two fixation figures are any suitable two locations of the display surface. In some embodiments, the display location of one or both the fixation figures on the display surface is operator-selectable, that is to say, the image provider is configured so that an operator is able to select a different-location image pair where the two fixation figures are displayed at desired display locations. In some such embodiments, the image provider is configured to generate a different-location image pair on receipt of a user- instruction which user instruction includes the desired display location of one or both of the fixation figures. Additionally or alternatively, in some embodiments the image provider includes multiple per-existing different-location image pairs having different display locations, and a user can select a specific different-location image pair having a desired display location for display.

Simultaneous image-pair display

In some embodiments, a device is configured to display the left eye image and corresponding right eye image of an image pair simultaneously on the display surface.

In some such embodiments, the image obstructor includes:

a left obstructor (called "screen" in the priority document) that blocks the view of a left eye to a right fixation figure of a corresponding right image and does not block the view of the left eye to a left fixation figure of a left image when the left eye image and right eye image are simultaneously displayed on the display surface; and

a right screen obstructor blocks the view of a right eye to a left fixation figure of a left eye image and does not block the view of the right eye to a right fixation figure of a right eye image when the left eye image and the right eye image are simultaneously displayed on the display surface.

For example, some such embodiments are similar or identical to 3D cinema glasses based on the use of two cross-polarized filters. Accordingly, in some such embodiments, the left eye image is cross-polarized relative to the right obstructor of the image obstructor and parallel-polarized relative to the left obstructor of the image obstructor; and the right eye image is cross-polarized relative to the left obstructor of the image obstructor and parallel-polarized relative to the right obstructor of the image obstructor. For example, some such embodiments are similar or identical to anaglyph (two-color) cinema glasses based on the use of two complementary-color lenses. Accordingly, in some such embodiments,

the left eye image is of a color absorbed by the right obstructor of the image obstructor and that passes through the left obstructor of the image obstructor; and

the right eye image is of a color absorbed by the left obstructor of the image obstructor and that passes through the right obstructor of the image obstructor.

For example, in some such embodiments the display device is similar or identical to virtual-reality headsets where the display surface is split into two separate individual display surfaces, one display surface for the left eye which is not viewable by the right eye and one display surface for the right eye which is not viewable by the left eye. In such embodiments, the human subject is not literally located at least 30 cm from the display surface, but the respective images are such that the human subject is virtually located at least 30 cm from the fixation figures displayed on the respective display surfaces. Commercially-available virtual reality headsets suitable for implementing such embodiments include HTC Vive™ by HTC corporation (Xindian District, New Taipei City, Taiwan), Oculus Rift™ by Oculus VR (Menlo Park, California, USA), Play Station VR by Sony Corporation (Minato, Tokyo, Japan), FOVE™ by Fove Inc. (San Mateo, California, USA) and Gear VR™ and ExynosVR™ by Samsung Group (Seoul, South Korea).

Alternating image-pair display

In some embodiments, a device is configured to alternatingly display the left eye image and corresponding right eye image of an image pair on the display surface, and

when the left eye image of the image pair is displayed on the display surface, the image obstructor blocks the view of a right eye to the display surface and allows view of a left eye to the display surface; and

when the right eye image of the image pair is displayed on the display surface, the image obstructor blocks the view of a left eye to the display surface and allows view of a right eye to the display surface.

In some such embodiments, the image obstructor is similar, analogous or identical to electronic shutter glasses, as known in the art of active shutter 3D systems, e.g. commercially available from XPand (Ljubljana, Slovenia). In Figure 2A, device 32 is configured to alternatingly display a left eye image and a right eye image of an image pair on display surface 36 and wirelessly coordinates the blocking of the view of the left and right eyes by image obstructor 42. Display rate

In some embodiments of alternating image-pair displays, the duration of display of a left eye image with concomitant blocking of the view of the corresponding right eye to the display surface and the duration of display of the right eye image with concomitant blocking of the view of the left eye to the display surface is operator-controllable.

In some embodiments, the alternating display is periodic at a repetition rate, in some embodiments, an operator-selectable rate. In some preferred embodiments, a periodic repetition rate is not less than 20 Hz, that is to say, that during a substantial portion of the time that the left eye image is displayed, the right image is not displayed and that during a substantial portion of the time that the right eye image is displayed, the left image is not displayed. In some embodiments, a substantial portion of time is not less than 80%, not less than 85%), not less than 90% and even not less than 95%.

It is important to note that at a repetition rate of 20 Hz, there exists a continuous 50 millisecond period during which both the left eye image and the right eye image are displayed only once, e.g., the left eye image for 25 milliseconds and the right eye image for 25 milliseconds) as 20Hz is the minimal rate for giving a human subject the illusion of a continuous image. However, in preferred embodiments, the periodic repetition rate is higher, e.g., not slower than 40Hz and even not slower than 60 Hz, in some preferred embodiments between 60Hz and 100 Hz. Eye Tracker

As understood from Background Section, tests for ocular misalignment require observation of the eyes gaze direction in order to detect fixation location and or change in gaze direction (as saccades) during a test.

In some instances, a device according to the teachings herein is used to observe ocular misalignment of a subject where eye movement is determined by an operator such as an ophthalmologist looking at an eye of a subject while a given test is performed in a manner similar or identical to the described for the prior art tests described in the Background.

In some embodiments, a device according to the teachings herein further comprises an eye-tracker (also called gaze-tracker) to identify and report the gaze direction of at least one, preferably both, of the two eyes looking at the display surface, preferably continuously at a rate of not slower than 10 Hz, not slower than 20 Hz and even at a rate of not slower than 30 Hz, e.g., an eye tracking kit by SensoMotoric Instruments, Teltow, Germany. In some embodiments, an eye tracker comprises an image acquirer such as a video camera and associated software to continuously acquire images of a left eye and to continuously determine the direction of the visual axis of the left eye at a rate of not slower than 10 Hz, not slower than 20 Hz and even at a rate of not slower than 30 Hz. In some embodiments, an eye tracker comprises an image acquirer such as a video camera and associated software to continuously acquire images of a right eye and to continuously determine the direction of the visual axis of the right eye at a rate of not slower than 10 Hz, not slower than 20 Hz and even at a rate of not slower than 30 Hz. In preferred embodiments, an eye tracker comprises one or more an image acquirers such as video cameras and associated software to continuously acquire images of both the left eye and the a right eye and to continuously determine the direction of the visual axis of the left eye and of the right eye at a rate of not slower than 10 Hz, not slower than 20 Hz and even at a rate of not slower than 30 Hz.

Embodiments which are implemented with devices similar to VR headsets are advantageously implemented using a virtual reality headset that includes an eye tracker for one or both eyes, e.g., a VR headset functionally associated with an eye tracking kit by SensoMotoric Instruments, Teltow, Germany.

In some embodiments, such as depicted in Figure 2A where the image obstructor is located between the eye and the display surface, the image obstructor is transparent to non- visible wavelengths of light (e.g., infrared) even when blocking the view of an eye of a subject to the display surface; and the device further comprises an eye tracker to identify and report the gaze direction of at least one, preferably both, of the two eyes, preferably continuously at a rate of not slower than 10 Hz, not slower than 20 Hz and even at a rate of not slower than 30 Hz In some such embodiments, the eye tracker comprises an eye-image acquirer for acquiring an image of the left eye and an image of the right eye of a subject viewing the display surface through the image obstructor. In some such embodiments, the image obstructor is transparent to non-visible wavelengths of light even when blocking the view of an eye of a subject to the display surface; and the device further comprises an eye- image acquirer for acquiring an image of the left eye and an image of the right eye of a subject viewing the display surface.

In some embodiments, the non-visible wavelengths are near-infrared wavelengths. In some embodiments, the eye-image acquirer is a video eye-image acquirer. In some embodiments, the eye-image acquirer is a component of an eye tracker.

In Figure 2B, an embodiment of a device according to the teachings herein, device 46 is schematically depicted. In device 46, image obstructor 42 is transparent to non-visible wavelengths of light even when blocking the view of an eye of a subject to the display surface. Device 46 further comprises a commercially-available near-infrared eye tracker 48 (Tobii AB, Danderyd, Sweden) providing the direction of the visual axes of the left eye and of the right eye of a subject viewing display surface 36.

Orientation determiner

Prior art methods for determining ocular misalignment

As is known to a person having ordinary skill in the art, an object (such as a fixation figure of the teachings herein) is viewed with the fovea of an eye of a person and the visual axis of the eye viewing the object is a virtual line passing through the fovea, pupil and the viewed object. Thus, to see an object with an eye, a person moves their head relative to the object and/or moves their eye relative to the head so that the visual axis of the eye is directed at the object.

In prior art methods for determining ocular misalignment, it is impossible to determine and account for what combination of moving the head and moving the eye relative to the head a subject performs to direct a visual axis of an eye at an object. As a result, ocular misalignment of a deviating eye of a subject can only be determined relative to a single orientation of the subject relative to an object. It is possible that some of the inaccuracies of prior art methods for determining ocular misalignment result from comparing results of multiple measurements where the orientation of the viewed object to the subject are different so that the orientation of the head to the body and of the eyes to the head of the subject are different in some of the measurements, for example, due to the subject moving to see better, natural fidgeting or due to discomfort during a lengthy testing period. Importantly, the measure of ocular deviation of a deviating eye measured using a prior art cover test is inherently flawed, since it is possible that when the non-deviating eye is covered and the deviating eye is required to fixate the subject may move their body and/or head relative to the viewed object.

As discussed in detail hereinbelow, in some embodiments of the teachings herein, the effect of the movement of the body or head of a subject that changes the orientation of the head relative to a viewed object during an test when determining ocular misalignment can be at least partially compensated for, and in some embodiments, entirely neutralized. Additionally, using such embodiments of the teachings herein, it is possible to determine the magnitude of misalignment of the deviating eye as a function of location of a non-deviating eye fixation figure relative to the head of the subject. Additionally, using such embodiments of the teachings herein, it is possible to determine the magnitude of misalignment of the deviating eye as a function of the orientation of the head relative to the body of the subject.

Embodiments with display device attached to the head of the subject

As noted above, some embodiments of the teachings herein which are implemented with a display device that is attached to the head of the subject, e.g., with components that are similar to or identical with VR headsets. Such embodiments often achieve more accurate results relative to prior art methods for determining ocular misalignment. Without wishing to be held to any one theory, it is currently believed that at least some of the superiority of the results arises from the fact that the orientation of the head of a subject relative to the display screen is constant. As a result, a given fixation figure remains in a fixed location of the display screen relative to the subject's head no matter how the subjects body or head move. When a fixation figure is maintained in a fixed location of the display surface throughout a test, the only way for the visual axis of an eye to be directed at the fixation figure is by rotating the eye relative to the head. As a result of eliminating changes to the visual axis caused by body and head movements, ocular misalignment tests performed using such embodiments have increased reproducibility and accuracy. Additionally, such embodiments allow determination of ocular misalignment as a function of the orientation of the head relative to the body, for instance, when the head is rotated left or right to look at the sides, or tilted upwards (nodding) to look upwards.

As noted above, some embodiments of devices according to the teachings herein provide for displaying multiple image pairs having fixation figures that are displayed at different locations on the display screen. Such embodiments allow performance of a test for ocular misalignment where ocular misalignment of a deviating eye is determined as a function of the orientation of the visual axis of the non-deviating eye relative to the head, by performing a test for ocular deviation multiple times where the fixation figure displayed along various gaze directions of the visual field by displaing the non-deviating eye fixation figure at a different location on the display screen. Embodiments with display device not-attached to the subject

In embodiments of the teachings herein where the display device is not attached to the subject, e.g. embodiments such as depicted in Figure 2A where the display device is a non- moving component located in front of the subject and the image obstructor is a component located between the display surface and the eyes of the subject, the subject can move their head and body relative to the display screen potentially leading to at least some of the challenges discussed above with reference to the prior art methods. However, it has been found that by determining the orientation of the head of the subject while performing ocular misalignment tests using such embodiments, it is possible to at least partially compensate for inaccuracies caused by motion of the head and body and thereby to provide results similar to those provided with embodiments where the display device is attached to the subject, and it is also possible to provide heretofore unavailable diagnostic information. Additionally, such embodiments allow determination of ocular misalignment as a function of the position of the head relative to the body (along any of the following planes: vertical, horizontal, torsional and depth), for instance, when the head is rotated left or right to look at the sides, or tilted upwards (nodding) to look upwards.

Accordingly, in some embodiments a device according to the teachings herein comprises an orientation-determiner for determining at least one of:

the distance between the head of a subject and the display surface;

the roll of the head of a subject relative to the display surface;

the pitch of the head of the subject relative to the display surface; and

the yaw of the head of the subject relative to the display surface.

In some such embodiments, the device further comprises an image-acquirer (e.g., a camera with associated suitably-configured image-analysis software) that acquires images of the head and/or body of the subject while the subject is being tested and analyzes the acquired images to determine one or more of the above-mentioned distance, pitch, roll and yaw.

That said, it is relatively challenging to directly determine distance, pitch, roll and yaw of the head of a human relative to a fixed display device from image analysis in conditions typically found when implementing the teachings herein. It has been found that a far simpler solution is to determine the orientation of an image obstructor worn on the head of the subject relative to the display surface as a measure of the orientation of the head of the subject.

Accordingly, in some embodiments a device according to the teachings herein comprises an orientation-determiner for determining at least one of: the distance between the image obstructor and the display surface as a measure of the distance between the head of the subject and the display surface;

the roll of the image obstructor relative to the display surface as a measure of the roll of the head of a subject relative to the display surface;

the pitch of the image obstructor relative to the display surface as a measure of the pitch of the head of a subject relative to the display surface; and

the yaw of the image obstructor relative to the display surface as a measure of the yaw of the head of a subject relative to the display surface.

In some such embodiments, the orientation-determiner comprises markers fixed on the image obstructor, preferably clearly discernible markers for example, fluorescent markers.

For instance, the relative orientation in an acquired image of at least two such markers placed one on the left side and one on the right side of an image obstructor can be used to calculate the distance (from the separation, in pixels, between the images of the markers in an acquired image), roll (from the difference in elevation and distance from a vertical center point, between the images of the markers in an acquired image) and yaw (from the difference in distance from a vertical center point, between the images of the markers in an acquired image).

For instance, the relative orientation in an acquired image of at least two such markers placed one above the other on an image obstructor can be used to calculate the distance (from the separation, in pixels, between the images of the markers in an acquired image), roll (from the difference in elevation and distance from a horizontal center point, between the images of the markers in an acquired image) and pitch (from the difference in distance from a horizontal center point, between the images of the markers in an acquired image).

In some embodiments, the orientation determiner comprises a camera and image analysis software associated therewith. In some such embodiments, the camera acquires an image of the markers and the associated software is used to:

identify the portions of an acquired image corresponding to the markers; and perform calculations (e.g., geometric and/or trigonometric calculations) to determine at least one of:

distance between the image obstructor and the display surface as a measure of the distance between the eyes of the subject and the display surface,

the pitch of the image obstructor relative to the display surface as a measure of the pitch of the head of a subject relative to the display surface; the pitch of the image obstructor relative to the display surface as a measure of the pitch of the head of a subject relative to the display surface; and

Device 46 depicted in Figure 2B, includes two distinct markers 50a and 50b secured on either side of image obstructor 42 and video camera 52 is directed to continuously capture images of markers 50a and 50b and provide these images to the computer that functions as image provider 40. The computer is configured (with the appropriate image analysis software) to accept the images and to continuously determine the distance between the image obstructor and the display surface, the pitch of the image obstructor relative to the display surface as a measure of the pitch of the head of a subject relative to the display surface; and the yaw of the image obstructor relative to the display surface as a measure of the yaw of the head of a subject relative to the display surface. As a result, markers 50a and 50b, camera 52 and the computer are together configured to function as an orientation determiner of device 46. At least one non-depicted marker located below either marker 50a or 50b allows determination of the roll of the image obstructor relative to the display surface as a measure of the roll of the head of a subject relative to the display surface.

As noted above, determining the orientation of the head of the subject (including the orientation of the image obstructor as a measure of the orientation of the head of the subject) relative to the display surface while performing ocular misalignment tests helps overcome at least some of the challenges described above. Specifically, a subject's head and body movements (e.g., resulting from fidgeting or fatigue) are measured and can be accounted for (by simple addition, subtraction and geometrical calculations) when determining ocular misalignment, thereby making measurements made during a single test more accurate reproducible.

Further and as noted above, some embodiments of devices according to the teachings herein provide for displaying multiple image pairs having fixation figures that are displayed at different locations on the display screen. Such embodiments allow performance of a test for ocular misalignment where ocular misalignment of a deviating eye is determined as a function of the orientation of the visual axis of the non-deviating eye relative to the head, by performing a test for ocular deviation multiple times where the fixation figure displayed to the non-deviating eye is displayed at a different location on the display screen. Additional diagnostic information is gained as to what extent the subject moves the head and body to orient the direction of gaze during the test. Controller

A device according to the teachings herein preferably comprises a controller. A controller preferably comprises a computer (e.g., a general purpose computer, a custom computer, a remote server). In device 46 depicted in Figure 2B, the controller is the laptop computer that serves as image provider 40. A controller of a device according to the teachings herein is functional to:

receive user instructions related to performing a test for ocular misalignment;

activate other components of the device to perform the received instructions;

display image pairs on the display surface;

if required, operate the image obstructor to allow viewing of image pairs displayed on display surface;

if present in the device, receive the direction of the visual axis (gaze direction) of the left eye and of the right of a tested subject from an eye tracker;

if present, receive the orientation of the head of a subject being tested relative to the display surface or the orientation of the image obstructor as a measure of the orientation of the head of the subject relative to the display surface.

Embodiments of the device according to the teachings herein may be used for implementing many and varied methods of performing ophthalmic tests, including the prior art cover test, prior art simultaneous prism cover test, prior art unilateral test, prior art alternate cover test and prior art alternate prism cover test, Particularly advantageous are devices where the display surface is attached to the head of a subject or which include an orientation determiner, for example, to neutralize or account for possible change in orientation of the head of the subject relative to a display surface. Embodiments of the device according to the teachings herein may also be used for implementing novel ophthalmic tests. Some such novel ophthalmic tests and novel methods of performing ophthalmic tests are the methods of performing ophthalmic tests according to the teachings herein that are described hereinbelow.

Methods according to the teachings herein

According to an aspect of some embodiments of the present invention, there is provided a method for performing an ophthalmic test useful for determining ocular misalignment in a subject having a left eye and a right eye, comprising: a. sequentially displaying multiple different image pairs to a subject, each image pair comprising a left eye image and a right eye image, the display of an image pair comprising concurrently displaying:

on a left display surface, displaying a left eye image of the image pair with a left fixation figure for viewing by the left eye of the subject, wherein the left fixation figure is not viewable by the right eye, and

on a right display surface displaying a right eye image of the image pair with a right fixation figure for viewing by the right eye of the subject, wherein the right fixation figure is not viewable by the left eye;

b. during the sequential display of image pairs, monitoring the gaze direction of at least one of the left eye and of the right eye, preferably both eyes, (e.g., with an eye tracker) to determine at least one result from the group of results consisting of:

a gaze direction of a monitored eye in relation to a displayed image pair,

whether or not the gaze direction of a monitored eye is directed at a fixation figure present in a respective the image of a displayed image pair, and

whether or not the gaze direction of a monitored eye is not directed at a fixation figure present in a respective the image of a displayed image pair; and

In some embodiments, the test is performed to gather information to help diagnose whether or not a subject has latent heterophoria. In some such embodiments, the result of the test is to gather information to help in determining the magnitude of ocular misalignment a subject diagnosed with latent heterophoria, e.g, the ocular misalignment of a deviating eye.

In some embodiments, the test is performed to gather information to help diagnose whether or not a subject has tropia. In some such embodiments, the result of the test is to gather information to help in determining the magnitude and/or the direction of ocular misalignment of a deviating eye of a subject diagnosed with tropia.

In some such embodiments, during the test the head of the subject can move relative to the display surface and the orientation of the head of the subject relative to the display surface is determined. In some such embodiments, the method further comprises accounting for changes in orientation of a subject's head relative to the display surface during performance of a test.

rejecting a determined result (e.g., the orientation of the head to the display surface indicated that any result is irrelevant, such as the subject shifted their head dramatically); associating a determined result with another determined result (e.g., grouping together results that were determined with the same or similar orientation of the head ); and modifying a determined gaze direction (e.g., correcting a magnitude of deviation for a change in orientation of the head).

Orientation of the eyes to the head

As discussed above with reference to the device according to the teachings herein, in prior art tests for the diagnosis of ocular misalignment, the object at which a subject is asked to look (the object being functionally analogous to a fixating figure according to the teachings herein) is located in front of the subject, approximately in the center of the field of view of the subject (i.e. primary gaze direction), and the deviation of a deviating eye is measured when the visual axis of the non-deviating eye is directed at the object. Some embodiments of the teachings herein are useful for determining the deviation of a deviating eye as a function of the direction of the visual axis of the non-deviating eye relative to the head of the subject. To this end, a given test is performed at least two times, where in at least two of the times the fixation figure that is displayed to the non-deviating eye is located at different locations of the display surface. While the head of the subject is maintained at the approximately same orientation relative to the display surface, the subject looks at the fixation figure with the non- deviating eye by rotating the non-deviating eye relative to the head. In such a way, the ocular deviation of the non-deviating eye as a function of the location of a fixation figure in a non- deviating eye image relative to the center of the display surface can be determined.

comparing the evidence provided by the first performance of the test and by the second performance of the test to determine whether a condition is dependent on the orientation of the non-deviating eye to the head. Such embodiments are useful for identifying a subject who suffers from tropia or phoria which manifestation or magnitude is dependent on the gaze direction of the non-deviating eye relative to the skull. Orientation of the head to the body

As noted above with reference to the device according to the teachings herein, in some instances the ocular misalignment of a subject is a function of the orientation of the head to the body of the subject, e.g., the ocular misalignment when the head is upright is different than the ocular misalignment when the neck is bent so that the subject looks down. Some embodiments of the teachings herein are useful for determining the deviation of a deviating eye as a function of the orientation of the head to the body of the subject.

Thus, in some embodiments, the method further comprises: performing the ophthalmic test at least twice, wherein the orientation of the head to the body of the subject in a first performance of the ophthalmic test is different from the orientation of the head to the body of the subject in a second performance of the ophthalmic test; and. comparing the evidence provided by the first performance of the test and by the second performance to determine whether a condition is dependent on the orientation of the head to the body. Such embodiments are useful for identifying a subject who suffers from tropia or phoria which manifestation or magnitude is dependent on the orientation of the head to the body.

In some embodiments, the test useful for determining ocular misalignment is at least one test selected from the group of tests consisting of: a cover test, e.g., similar to a prior art cover test as described with reference to Figure 1 in the Background; an unilateral test, e.g., similar to a prior art unilateral cover test, as described in the Background; an alternate cover test, e.g., similar to a prior art alternate cover test, as described in the Background Section; a modified unilateral cover test (also called simultaneous cover test) according to the teachings herein, useful for finding evidence to determine the presence of ocular misalignment attributable to tropia and/ or for determining the magnitude and/or direction of ocular misalignment attributable to tropia in a tested subject according to the teachings herein, described herein in detail with reference to Figures 3 A and 3B; and a modified alternate cover test according to the teachings herein, described herein in detail with reference to Figures 4A, 4B and 4C.

Modified unilateral cover test

A first specific embodiment of an ophthalmic test according to the teachings herein resembles some aspects of a prior art unilateral cover test and is therefore called a "modified unilateral cover test".

A modified unilateral cover test according to the teachings herein is, in some embodiments, used for determining the presence and/or magnitude of ocular misalignment in a subject having tropia, but in some embodiments is also useful for diagnosing tropia and identifying which eye is the deviating eye.

In brief summary, preferred embodiments of the modified unilateral cover test according to the teachings herein include:

1. establishing conditions of binocular vision;

2. following 1, preventing a first eye from seeing a fixation figure;

3. following 2, determining whether or not the second eye moves;

4. following 3, allowing the first eye to see a fixation figure; and

5. following 3. determining whether a second eye that moved in 3 moved back to the original position in 1. In some embodiments, if a second eye did not move in 3, 1-5 are repeated where the two eyes are switched.

In some embodiments, the modified unilateral cover test according to the teachings herein is used for diagnosis of tropia in a subject and identification of which eye is the deviating eye. Such an embodiment is described with reference to Figure 3A. Specifically, according to an aspect of some embodiments of the present invention, there is provided a method for finding evidence to determine the presence of ocular misalignment attributable to tropia in a subject having a first eye and a second eye, comprising:

a. in 54, concurrently:

on a first display surface, displaying a first image with a first fixation figure for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye, and on a second display surface, displaying a second image with a second fixation figure for viewing with the second eye, wherein the second fixation figure is not viewable by the first eye, wherein the location of the first fixation figure and the second fixation figure on the respective display surfaces is the same (e.g., an identical- location image pair as described above);

b. in 56, subsequent to 'a', while monitoring the second eye for refixation motion: preventing the first eye from seeing any fixation figure, and on the second display surface, displaying an image with a fixation figure for viewing with the second eye;

c. in 58, subsequent to 'b', while monitoring the second eye for motion attributable to loss of fixation:

on the first display surface, displaying a first image with a first fixation figure for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye, and on the second display surface, displaying a second image with a second fixation figure for viewing with the second eye, wherein the second fixation figure is not viewable by the first eye, wherein the location of the first fixation figure and the second fixation figure on the respective display surfaces is the same (e.g., an identical-location image pair as described above);

d. in 60, accepting as evidence that the second eye is a non-deviating eye if no movement of the second eye is observed in 'b' and/or 'c', 62; and

accepting as evidence that the subject has tropia and the second eye is a deviating eye if movement of the second eye is observed in 'b' and/or 'c', 64. In some such embodiments, the location of the first fixation figure on the first display surface in 'a' and in 'c' is the same.

Typically, embodiments of a modified unilateral cover test as described immediately hereinabove with reference to Figure 3 A are performed at least once for each eye, at least once where the left eye is the first eye and at least once where the right eye is the first eye. Although a single such test for each eye is typically sufficient, in preferred embodiments each eye is tested multiple times to increase confidence in the result. In some automated embodiments that are performed under control of a computer (e.g., using a device 46 of Figure 2B), multiple such tests can be performed for each eye in a period of a minute. That said, the number of repetitions is typically a decision made by a medical practitioner.

In some embodiments, a modified unilateral cover test according to the teachings herein is used for helping determine the magnitude and/or direction of ocular misalignment in a subject having tropia. Specifically, according to an aspect of some embodiments of the present invention, there is provided a method for determining the magnitude and/or direction of ocular misalignment attributable to tropia in a subject having a first non-deviating eye and a second deviating eye, comprising:

a. in 66, concurrently:

on a first display surface, displaying a first image with a first fixation figure for viewing with the first non-deviating eye, wherein the first fixation figure is not viewable by the second deviating eye, and

on a second display surface, displaying a second image with a second fixation figure for viewing with the second deviating eye, wherein the second fixation figure is not viewable by the first non-deviating eye,

wherein the location of the first fixation figure and the second fixation figure on the respective display surfaces is different (e.g., a different-location image pair). As a result, the first non-deviating eye is fixated on the fixation figure while the second deviating eye is not fixated. b. in 68, subsequent to 'a', while monitoring the second deviating eye for refixation motion: preventing the first non-deviating eye from seeing any fixation figure, and on the second display surface, displaying an image with a fixation figure for viewing with the second deviating eye. As a result, the first non-deviating eye loses fixation and becomes not-fixated while the second deviating eye becomes fixated on the fixation figure.

c. in 70, subsequent to 'b', while monitoring the second deviating eye for motion attributable to loss of fixation:

on the first display surface, displaying a first image with a first fixation figure for viewing with the first non-deviating eye, wherein the first fixation figure is not viewable by the second deviating eye, and on the second display surface, displaying a second image with a second fixation figure for viewing with the second deviating eye, wherein the second fixation figure is not viewable by the first non-deviating eye, wherein the location of the first fixation figure and the second fixation figure on the respective display surfaces is different (e.g., a different-location image pair). As a result, the first non-deviating eye becomes fixated on the fixation figure while the second deviating eye loses fixation and becomes not-fixated.

d. in 72, accepting as evidence that the difference between the location of the first fixation figure on the first display surface and the location of the second fixation figure on the second display surface in 'b' is indicative of the magnitude and direction of ocular misalignment attributable to tropia if no movement of the second eye is observed in 'b' and/or 'c' 74; wherein the location of the first fixation figure on the first display surface in 'a' and in 'c' is the same. Typically, an exact value for the magnitude and direction of ocular misalignment can be calculated from the difference using simple geometry.

In some such embodiments the method further comprises: if the movement of the second eye is observed in 'b' and/or 'c' given a preceding difference between the location of the first fixation figure on the first display surface and the location of the second fixation figure on the second display surface 76, then repeating 'a', 'b' and 'c' where the difference between the location of the first fixation figure on the first display surface and the location of the second fixation figure on the second display surface is different from the preceding difference 78.

Typically the difference in location of the succeeding 'a', 'b' and 'c' is based on the direction and magnitude of the movement of the second eye observed in one or more preceding 'b' and/or 'c'. In some embodiments, the difference is determined by the person administering the test based on experience or preferred calculations. In some embodiments, the difference in location of the succeeding 'a', 'b' and 'c' is automatically calculated based on the direction and magnitude of the movement of the second eye observed in one or more preceding 'b' and/or 'c' using any suitable algorithm, e.g., variants of a two-dimensional binary search algorithm.

For example, in some embodiments a first 'a', 'b' and 'c' is performed wherein the locations of the first fixation figure and the second fixation figure on the respective display surfaces are identical and the direction of the movement of the second eye in 'b' and 'c' is recorded. A second 'a', 'b' and 'c' is performed wherein the locations of the first fixation figure and the second fixation figure on the respective display surfaces are different by a random direction and magnitude; and the direction of the movement of the second eye in 'b' and 'c' is recorded. The actual ocular deviation is calculated by triangulation based on the two recorded directions of movement of the second eye, and a third 'a', 'b' and 'c' is then performed wherein the locations of the first fixation figure and the second fixation figure on the respective display surfaces are different by an amount based on the results of the triangulation.

Typically, in embodiments of a modified unilateral cover test as described immediately hereinabove with reference to Figure 3B, the test is performed with multiple location differences at least until a location of a fixation figure displayed to the deviating eye in 68 leads to no deviating eye fixation movement in 66 to 68 or loss of fixation movement in 68 to 70 as such lack of movement is indicative of the ocular misalignment attributable to tropia. That said, typically the test is repeated multiple times to confirm that a given location difference leads to no such movement and thereby to increase the confidence in achieved results. In some automated embodiments that are performed under control of a computer (e.g., using a device 46 of Figure 2B), multiple such tests can be performed in a period of a minute. That said, the number of repetitions is typically a decision made by a medical practitioner.

In some typical embodiments of a modified unilateral cover test according to the teachings herein, the fixation figure displayed to the first eye or to the non-deviating eye is located in front of the subject, approximately in the center of the field of view of the subject. As a result, the test identifies the presence or absence of tropia and/or the magnitude and/or direction of the ocular misalignment of tropia when the eyes are straight ahead in the head and the head is oriented normally relative to the body. In some embodiments, it is desirable to evaluate the presence, absence, magnitude and/or direction of ocular misalignment when the first eye or non-deviating eye is not oriented straight ahead relative to the head, but is rotated to a different orientation relative to the head. Such embodiments are preferably performed as described above, for example, using a device according to the teachings herein. In some embodiments, it is desirable to evaluate the presence, absence, magnitude and/or direction of ocular misalignment when the head is not oriented normally relative to the body, but is at a different orientation, relative to the body, e,g, tilted downwards or turned to a side. Such embodiments are preferably performed as described above, for example, using a device according to the teachings herein, using an orientation determiner.

Modified alternate cover test

A second specific embodiment of an ophthalmic test according to the teachings herein resembles some aspects of a prior art alternate cover test and is therefore called a "modified alternate cover test".

A modified alternate cover test according to the teachings herein is, in some embodiments, primarily used for finding evidence of the presence of ocular misalignment attributable to either or both tropia and latent heterophoria determining the magnitude and/or direction of ocular misalignment attributable to either or both tropia and latent heterophoria.

In brief summary, preferred embodiments of the modified alternate cover test according to the teachings herein include:

1. establishing conditions of binocular viewing with an identical-location image pair;

2. following 1, display an image having a fixation figure at an initial location to a first eye and prevent the second eye from seeing any fixation figure for at least 6 seconds to allow the second eye to move to its rest position;

3. following 2 or 7, while displaying the same image to the first eye, display an image with a fixation figure at a location to the second eye while preventing binocular viewing of the fixation figures. If the second eye moves, calculate where the second eye was gazing during the rest position and prepare an updated image for display to the second eye in a future 3, the updated image having a fixation figure located at a location for viewing by the second eye in its rest position;

4. following 3, reestablish conditions of binocular viewing;

5. following 4, display an image having a fixation figure at a location to the second eye and prevent the first eye from seeing a fixation figure for at least 6 seconds to allow first eye to move to its rest position;

6. following 5, while displaying the same image to the second eye, display an image with a fixation figure to the first eye to reestablish binocular viewing. If the first eye moves, calculate where the first eye was gazing during the rest position and prepare an updated image for display to the first eye in a future 6, the updated image having a fixation figure located at a location for viewing by the first eye in its rest position;

7. return to 3

8. when sufficient 3, 4, 5, 6, 7 have been performed:

relate the location of a fixation figure viewed by the second eye that in 3 did not lead to movement of the second eye to the rest position of the second eye;

relate the location of a fixation figure viewed by the first eye that in 5 did not lead to movement of the first eye to the rest position of the first eye; and

identify the difference between the gaze direction of the two eyes in the respective rest position as the angle of the ocular deviation.

In some embodiments, the modified alternate cover test according to the teachings herein is used for finding evidence of the presence of ocular misalignment attributable to tropia and/or latent heterophoria. The test differentiates between a subject having neither tropia nor phoria, and subjects having tropia alone, phoria alone or both tropia and phoria. Such an embodiment is described with reference to Figure 4A. Specifically, according to an aspect of some embodiments of the present invention there is provided a method for finding evidence of the presence of ocular misalignment attributable to tropia and/or latent heterophoria in a subject having a first eye and a second eye, comprising: :

a. in 80, concurrently:

on a first display surface, displaying a first image with a first fixation figure for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye, and

on a second display surface, displaying a second image with a second fixation figure for viewing with the second eye, wherein the second fixation figure is not viewable by the first eye,

wherein the locations of the first fixation figure and the second fixation figure on the respective display surfaces are the same (e.g., an identical -location image pair as described above;

b. in 82, subsequent to 'a',

on the first display surface, displaying a first image with a first fixation figure at a location LI of the first display surface for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye, and preventing the second eye from seeing any fixation figure, for a period of time sufficient to allow the second eye to move to a rest position while the first eye is fixated on the first fixation figure (typically the period of time being not less than 6 seconds);

c. in 84, subsequent to b, while monitoring the second eye for refixation motion:

wherein:

in 86, accepting as evidence that the second eye is free of ocular misalignment attributable to tropia and latent heterophoria if no refixation movement of the second eye is observed in 'c', 88, and

accepting as evidence that the second eye has ocular misalignment attributable to tropia and/or latent heterophoria if refixation movement of the second eye is observed in 'c', 90. In some embodiments, a modified alternate cover test according to the teachings herein is used for helping determine the magnitude and direction of ocular misalignment attributable to tropia and/or latent heterophoria in a subject. In some embodiments, the test determines the total magnitude and direction of ocular misalignment: for subjects having tropia alone, the magnitude and direction of ocular misalignment attributed to the tropia; for subjects having phoria alone, the magnitude and direction of ocular misalignment attributed to the phoria; and for subjects having both tropia and phoria, the magnitude and direction of ocular misalignment that is the sum of misalignment attributed to the phoria and to the tropia. Such an embodiment is described with reference to Figure 4B. Specifically, according to an aspect of some embodiments of the present invention there is provided a method for determining the magnitude and/or direction of ocular misalignment attributable to tropia and/or latent heterophoria in a subject having a first eye and a second eye, comprising:

a. in 92, concurrently: on a first display surface, displaying a first image with a first fixation figure for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye, and

wherein the locations of the first fixation figure and the second fixation figure on respective the display surfaces are the same (e.g., an identical -location image pair); b. in 94, subsequent to 'a',

on the first display surface, displaying a first image with a first fixation figure at a location LI of the first display surface for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye and preventing the second eye from seeing any fixation figure, for a period of time sufficient to allow the second eye to move to a rest position while the first eye is fixated on the first fixation figure (typically the period of time being not less than 6 seconds);

c. in 96, subsequent to 'b', while monitoring the second eye for refixation motion:

on the first display surface, displaying the first image of 'b' with the first fixation figure at the location LI of the first display surface for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye, and

on the second display surface, displaying a second image with a second fixation figure at a location L2 of the second display surface for viewing with the second eye, wherein the second fixation figure is not viewable by the first eye,

wherein the location of the first fixation figure LI and the location of the second fixation figure L2 on the respective display surfaces are not the same;

wherein:

in 98, if no refixation movement of the second eye is observed in 'c,' then the second fixation figure at L2 is aligned with the visual axis of the second eye so that the location L2 on the second display surface is accepted as indicative of the magnitude and direction of ocular misalignment of the second eye attributable to tropia, latent heterophoria or a combination of tropia and latent heterophoria, 100.

In some embodiments, the method further comprises: if the refixation movement of the second eye is observed in a preceding 'c' with a given location of the second fixation figure L2 on the second display surface 102, then the second fixation figure at L2 is not aligned with the visual axis of the second eye. L2 is updated and 'b' and 'c' are repeated with an updated location L2 of the second fixation figure on the second display surface different from the preceding given location L2, 94.

Embodiments of a modified alternate cover test such as the described above with reference to Figure 4A and 4B are performed at least once for each eye, at least once where the left eye is the first eye and at least once where the right eye is the first eye. Although a single such test for each eye is typically sufficient, in preferred embodiments each eye is tested multiple times to increase confidence in the result. That said, the number of repetitions is typically a decision made by a medical practitioner.

In some embodiments of the modified alternate cover test such as the described above with reference to Figure 4A and 4B, the first eye is the left eye and the second eye is the right eye. In some embodiments of the modified alternate cover test methods, the first eye is the right eye and the second eye is the left eye. In some embodiments of the modified alternate cover test methods, 'b' and a following 'c' are performed at least two times, one of the two times where the first eye is the left eye and the second eye is the right eye, and the other of the two times where the first eye is the right eye and the second eye is the left eye.

A preferred embodiment of a modified alternate cover test according to the teachings herein determining the magnitude and/or direction of ocular misalignment attributable to tropia and/or latent heterophoria in a subject having a first eye and a second eye is described with reference to Figure 4C. The embodiment described with reference to Figure 4C can be considered to be two instances of the embodiment described with reference to Figure 4B, a first instance for a first eye (e.g., left eye) and the second instance for a second eye (e.g., right eye), where the two embodiments are interleaved. Specifically, the two eyes are alternatingly prevented from seeing a fixation figure to adopt a respective rest position (106 for the second eye, 116 for the first eye) and then shown a fixation figure at a changing location (L2 for the second eye in 108, LI for the first eye in 104) while monitoring for refixation movement (110 for the second eye, 118 for the first eye). If refixation movement is observed, the respective LI or L2 is updated (114 for L2, 122 for LI). When no refixation movement is observed for either eye when, from a rest position, the eye is shown a fixation figure at a respective location LI or L2 (112 for the second eye and 120 for the first eye), the magnitude and direction of ocular misalignment of the first eye relative to the second eye attributable to tropia, latent heterophoria or a combination of tropia and latent heterophoria is known. Such interleaved embodiments allow a significant savings in time as both eyes are tested together. Importantly, it has been found that in some such embodiments, the time-consuming and often inaccurate step of calibrating the eye-tracker used for monitoring whether or not an eye undergoes fixation movement is obviated. In such embodiments no initial calibration of the eye-tracker is needed because the magnitude and direction of the ocular misalignment is determined in terms of one eye relative to the other.

This, according to an aspect of some embodiments of the teachings herein, there is provided a method for determining the magnitude and/or direction of ocular misalignment attributable to tropia and/or latent heterophoria in a subject having a first eye and a second eye, comprising:

a. concurrently:

on a first display surface, displaying a first image with a first fixation figure at a location LI of the display surface for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye, and on a second display surface, displaying a second image with a second fixation figure at a location L2 of the display surface for viewing with the second eye, wherein the second fixation figure is not viewable by the first eye,

b. subsequent to 'a',

c. subsequent to 'b', while monitoring the second eye for refixation motion:

on the first display surface, displaying a first image with a first fixation figure at the location LI of the first display surface for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye, and

if an updated L2 exists from a preceding 'c', setting L2 to be the updated L2, on the second display surface, displaying a second image with a second fixation figure at a location L2 of the second display surface for viewing with the second eye, wherein the second fixation figure is not viewable by the first eye,

wherein:

if no refixation movement of the second eye is observed in 'c,' accepting the location of the second fixation figure L2 on the second display surface as indicative of the magnitude and direction of ocular misalignment of the second eye attributable to tropia, latent heterophoria or a combination of tropia and latent heterophoria, and if the refixation movement of the second eye is observed in 'c' with a given location of the second fixation figure L2, defining an updated L2 different from L2;

d. subsequent to 'c',

on the second display surface, displaying a second image with a second fixation figure at location L2 of the second display surface for viewing with the second eye, wherein the second fixation figure is not viewable by the first eye, and preventing the first eye from seeing any fixation figure, for a period of time sufficient to allow the first eye to move to a rest position while the second eye is fixated on the second fixation figure; e. subsequent to 'd', while monitoring the first eye for refixation motion:

if an updated LI exists from a preceding 'e', setting LI to be the updated LI, on the first display surface, displaying a first image with a first fixation figure at the location LI of the first display surface for viewing with the first eye, wherein the first fixation figure is not viewable by the second eye, and on the second display surface, displaying a second image with a second fixation figure at the location L2 of the second display surface for viewing with the second eye, wherein the second fixation figure is not viewable by the first eye,

wherein:

if no the refixation movement of the first eye is observed in 'e,' accepting the location of the first fixation figure LI on the first display surface as indicative of the magnitude and direction of ocular misalignment of the first eye attributable to tropia, latent heterophoria or a combination of tropia and latent heterophoria, and

if the refixation movement of the first eye is observed in a preceding 'e' with a given location of the second fixation figure LI on the first display surface

f. optionally, subsequent to 'e', repeating from 'b'.

Typically the location of an updated LI or L2 is based on the direction and magnitude of the movement of the respective eye observed in one or more preceding 'c'. In some embodiments, the updated LI or L2 is determined by the person administering the test based on experience or preferred calculations. In some embodiments, the updated LI or L2 is automatically calculated based on the direction and magnitude of the movement of the respective eye observed in one or more preceding 'c' using any suitable algorithm, e.g., variants of a two-dimensional binary search algorithm. In some embodiments, an updated LI or L2 is calculated using tri angulation, analogously to the described above for embodiments of the modified unilateral cover test. Typically, in embodiments of a modified alternate cover test as described hereinabove with reference to Figure 4B and 4C, the test is performed repeatedly with multiple different values of LI and L2 at least until a location LI or L2 of a fixation figure displayed to a respective eye in 96 or 108 and 104 leads to no fixation movement in 94 to 96 or 106 to 108 and 116 to 106 That said, typically a test is repeated multiple times to confirm that a given LI and/or L2 leads to no such movement and thereby to increase the confidence in achieved results. In some automated embodiments that are performed under control of a computer (e.g., using a device 46 of Figure 2B), multiple such tests can be performed in a period of a minute. That said, the number of repetitions is typically a decision made by a medical practitioner.

In some typical embodiments of a modified alternate cover test according to the teachings herein, the fixation figures displayed to the eyes are located in front of the subject, approximately in the center of the field of view of the subject. As a result, the test identifies the presence or absence of tropia and/or phoria and/or the magnitude and/or direction of the ocular misalignment of tropia and/or phoria when the eyes are substantially straight ahead in the head and the head is oriented normally relative to the body. In some embodiments, it is desirable to evaluate the presence, absence, magnitude and/or direction of ocular misalignment related to tropia and/or phoria when the eyes are not oriented straight ahead relative to the head, but are rotated to a different orientation relative to the head. Such embodiments are preferably performed as described above, for example, using a device according to the teachings herein. In some embodiments, it is desirable to evaluate the presence, absence, magnitude and/or direction of ocular misalignment related to tropia and/or phoria when the head is not oriented normally relative to the body, but is at a different orientation, relative to the body, e,g, tilted downwards or turned to a side. Such embodiments are preferably performed as described above, for example, using a device according to the teachings herein, using an orientation determiner.

Embodiments of a modified unilateral cover test or of a modified alternate cover test such as described above with reference to Figure 3A, 3B, 4A and 4B can be implemented with any suitable device, for example, a device 46 depicted in Figure 2B. In preparation for the test, a subject 38 is fitted with an image obstructor 42 as described above, so that subject 38 is able to see display surface 36. The operator (a health care professional such as an ophthalmologist) decides whether or not subject 38 wears corrective eyeglasses during the test. The operator activates to the computer of device 46 to operate as a controller. Eye tracker 48 is activated to provide the direction of the visual axes of the left eye and the right eye of the subject to the controller. Camera 52 and related software are activated to function as an orientation determiner to determine the distance, pitch and roll of the image obstructor relative to display surface 36.

In some embodiments of any of the methods described herein, preventing an eye from seeing any fixation figure includes: on a respective display surface displaying an image devoid of a fixation figure for viewing by the eye.

In some embodiments of any of the methods described herein, preventing an eye from seeing any fixation figure includes: occluding the view of the eye to a respective display surface with an occluder. In such embodiments, the line of sight of the eye to the display surface is is blocked, for example, using a prior art paddle or by darkening the lens of an image obstructor.

In some embodiments of any of the methods described herein, during performance of a test the display surfaces are attached to the head of the subject, the test surfaces thereby having a fixed orientation and distance relative to the head of the subject..

In some embodiments, during performance of a test the head of the subject can move relative to the display surfaces and the orientation of the head of the subject relative to the display surfaces is determined. The results of the method can then optionally be modified or interpreted in light of the the determined orientation.

In some embodiments of any of the methods described herein, the concurrent displaying is simultaneous displaying of the two images of an image pair (left and right images, first and second images), that is to say, both the images appear on a respective display surface simultaneously.

In some embodiments of any of the methods described herein, the concurrent displaying is alternate displaying of the two images of an image pair (left and right images, first and second images), in some embodiments at a rate of of not less than 20 Hz. Alternate displaying is as described above with reference to embodiments of a device according to the teachings herein.

In some embodiments of any of the methods described herein, the two display surfaces (left and right display surface, first and second display surfaces) are physically the same display surface. Such embodiments include embodiments implemented on a device such as device 32 depicted in Figure 2 A or device 46 depicted in Figure 2B.

In some embodiments of any of the methods described herein, the two display surfaces (left and right display surface, first and second display surfaces) are physically different display surfaces. Such embodiments include embodiments implemented using VR headsets where either there are two distinct display screens, one for either eye, or there is a single display screen that is functionally divided into a portion for viewing by a left eye and a portion for viewing by a right eye. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. In case of conflict, the specification, including definitions, takes precedence.

As used herein, the terms "comprising", "including", "having" and grammatical variants thereof are to be taken as specifying the stated features, integers, steps or components but do not preclude the addition of one or more additional features, integers, steps, components or groups thereof.

As used herein, the indefinite articles "a" and "an" mean "at least one" or "one or more" unless the context clearly dictates otherwise.

As used herein, when a numerical value is preceded by the term "about", the term "about" is intended to indicate +/-10%.

As used herein, a phrase in the form "A and/or B" means a selection from the group consisting of (A), (B) or (A and B). As used herein, a phrase in the form "at least one of A, B and C" means a selection from the group consisting of (A), (B), (C), (A and B), (A and C), (B and C) or (A and B and C).

Embodiments of methods and/or devices described herein may involve performing or completing selected tasks manually, automatically, or a combination thereof. Some methods and/or devices described herein are implemented with the use of components that comprise hardware, software, firmware or combinations thereof. In some embodiments, some components are general-purpose components such as general purpose computers or digital processors. In some embodiments, some components are dedicated or custom components such as circuits, integrated circuits or software.

For example, in some embodiments, some of an embodiment is implemented as a plurality of software instructions executed by a data processor, for example which is part of a general-purpose or custom computer. In some embodiments, the data processor or computer comprises volatile memory for storing instructions and/or data and/or a non-volatile storage, for example, a magnetic hard-disk and/or removable media, for storing instructions and/or data. In some embodiments, implementation includes a network connection. In some embodiments, implementation includes a user interface, generally comprising one or more of input devices (e.g., allowing input of commands and/or parameters) and output devices (e.g., allowing reporting parameters of operation and results.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the scope of the appended claims.

Citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the invention.

Section headings are used herein to ease understanding of the specification and should not be construed as necessarily limiting.

Claims

CLAIMS:

1. A method for performing an ophthalmic test useful for determining ocular misalignment in a subject having a left eye and a right eye, comprising:

a. sequentially displaying multiple different image pairs to a subject, each said image pair comprising a left eye image and a right eye image, said display of an image pair comprising concurrently displaying:

on a left display surface, displaying a left eye image of said image pair with a left fixation figure for viewing by the left eye of the subject, wherein said left fixation figure is not viewable by the right eye, and

on a right display surface displaying a right eye image of said image pair with a right fixation figure for viewing by the right eye of the subject, wherein said right fixation figure is not viewable by the left eye;

b. during said sequential display of image pairs, monitoring the gaze direction of at least one of the left eye and of the right eye to determine at least one result from the group of results consisting of:

a gaze direction of a monitored eye in relation to a displayed image pair,

whether or not the gaze direction of a monitored eye is directed at a fixation figure present in a respective said image of a displayed image pair, and

whether or not the gaze direction of a monitored eye is not directed at a fixation figure present in a respective said image of a displayed image pair; and

c. from said at least one determined result providing evidence for at least one condition selected from the group consisting of:

a presence or an absence of ocular misalignment of the subject,

a direction of ocular misalignment of the subject,

a magnitude of ocular misalignment of the subject,

which eye of the subject is a non-deviating eye,

which eye of the subject is a deviating eye,

a direction of deviation of a deviating eye of the subject, and

a magnitude of deviation of a deviating eye of the subject.

2. The method of claim 1, further comprising:

during said sequential displaying of multiple different image pairs, displaying at least one single-fixation image pair comprising a left eye image and a right eye image, wherein:

a first image of said single-fixation image pair includes a single fixation figure; and a second image of said single-fixation image pair is devoid of any fixation figure.

3. The method of claim 2, further comprising:

monitoring the gaze direction of at least one of the left eye and of the right eye to determine at least one result from the group of results consisting of:

the gaze direction of a monitored eye when said second image devoid of any fixation figure is displayed; and

the gaze direction of a monitored eye when a displayed said second image devoid of any fixation figure is replaced with a succeeding image including a fixation figure.

4. The method of any one of claims 1 to 3, wherein during said sequential display of said image pairs, said left display surface and said right display surface are attached to the head of the subject, [thereby having a fixed orientation and distance relative to the head of the subject]

5. The method of any one of claims 1 to 3, wherein during said sequential display of said image pairs, the head of the subject can move relative to said left display surface and said right display surface.

6. The method of claim 6, further comprising:

during said sequential display of said image pairs, determining an orientation of the head of the subject relative to said display surfaces; and

based one said determined orientation at least one of:

rejecting a said determined result;

associating a determined result with another determined result; and

modifying a determined gaze direction.

7. The method of any one of claims 1 to 6, wherein the subject has at least one non- deviating eye and a second eye, the method further comprising:

performing the ophthalmic test at least twice, in a first performance of the test, on said display surface viewed by the non-deviating eye, displaying a fixation figure in a first location of said display surface, and in a second performance of the test, on said display surface viewed by the non- deviating eye, displaying a fixation figure in a second location of said display surface different from said first location, so that the orientation of the non-deviating eye relative to the head in said first performance of the test is different from the orientation of the non-deviating eye relative to the head in said second performance of the test; and

comparing the evidence provided by said first performance and by said second performance to determine whether a condition is dependent on the orientation of the non-deviating eye to the head.

8. The method of any one of claims 1 to 7, further comprising:

performing the ophthalmic test at least twice, wherein the orientation of the head to the body of the subject in a first performance of the ophthalmic test is different from the orientation of the head to the body of the subject in a second performance of the ophthalmic test; and

comparing the evidence provided by said first performance and by said second performance to determine whether a condition is dependent on the orientation of the head to the body.

9. A method for finding evidence to determine the presence of ocular misalignment attributable to tropia in a subject having a first eye and a second eye, comprising:

a. concurrently:

on a first display surface, displaying a first image with a first fixation figure for viewing with the first eye, wherein said first fixation figure is not viewable by the second eye, and

on a second display surface, displaying a second image with a second fixation figure for viewing with the second eye, wherein said second fixation figure is not viewable by the first eye,

wherein the location of said first fixation figure and said second fixation figure on respective said display surfaces is the same;

b. subsequent to 'a', while monitoring the second eye for refixation motion:

preventing the first eye from seeing any fixation figure, and on said second display surface, displaying an image with a fixation figure for viewing with the second eye;

on said first display surface, displaying a first image with a first fixation figure for viewing with the first eye, wherein said first fixation figure is not viewable by the second eye, and

on said second display surface, displaying a second image with a second fixation figure for viewing with the second eye, wherein said second fixation figure is not viewable by the first eye,

d. accepting as evidence that the second eye is a non-deviating eye if no said movement of the second eye is observed in 'b' and/or 'c'; and

10. The method of claim 9, wherein the location of said first fixation figure on said first display surface in 'a' and in 'c' is the same.

11. A method for determining the magnitude and/or direction of ocular misalignment attributable to tropia in a subject having a first non-deviating eye and a second deviating eye, comprising:

a. concurrently:

on a first display surface, displaying a first image with a first fixation figure for viewing with the first non-deviating eye, wherein said first fixation figure is not viewable by the second deviating eye, and

on a second display surface, displaying a second image with a second fixation figure for viewing with the second deviating eye, wherein said second fixation figure is not viewable by the first non-deviating eye,

wherein the location of said first fixation figure and said second fixation figure on respective said display surfaces is different;

b. subsequent to 'a', while monitoring the second deviating eye for refixation motion:

preventing the first non-deviating eye from seeing any fixation figure, and on said second display surface, displaying an image with a fixation figure for viewing with the second deviating eye;

on said first display surface, displaying a first image with a first fixation figure for viewing with the first non-deviating eye, wherein said first fixation figure is not viewable by the second deviating eye, and

on said second display surface, displaying a second image with a second fixation figure for viewing with the second deviating eye, wherein said second fixation figure is not viewable by the first non-deviating eye,

wherein the location of said first fixation figure and said second fixation figure on respective said display surfaces is different; and

d. accepting as evidence that the difference between the location of said first fixation figure on said first display surface and the location of said second fixation figure on said second display surface in 'b' is indicative of the magnitude and direction of ocular misalignment attributable to tropia if no said movement of the second eye is observed in 'b' and/or 'c';

wherein the location of said first fixation figure on said first display surface in 'a' and in 'c' is the same.

12. The method of claim 11, further comprising:

if said movement of the second eye is observed in 'b' and/or 'c' given a preceding difference between the location of said first fixation figure on said first display surface and the location of said second fixation figure on said second display surface, then repeating a, b and c where the difference between the location of said first fixation figure on said first display surface and the location of said second fixation figure on said second display surface is different from said preceding difference.

13. The method of any one of claims 9 to 12, wherein said preventing the first eye from seeing any fixation figure includes: blocking the view of the first eye to said first display surface.

14. The method of any one of claims 9 to 12, wherein said preventing the first eye from seeing any fixation figure includes: on said first display surface, displaying an image devoid of any fixation figure.

15. A method for finding evidence of the presence of ocular misalignment attributable to tropia and/or latent heterophoria in a subject having a first eye and a second eye, comprising: a. concurrently:

wherein the locations of said first fixation figure and said second fixation figure on respective said display surfaces are the same;

b. subsequent to 'a',

on said first display surface, displaying a first image with a first fixation figure at a location LI of said first display surface for viewing with the first eye, wherein said first fixation figure is not viewable by the second eye, and preventing the second eye from seeing any fixation figure, for a period of time sufficient to allow the second eye to move to a rest position while the first eye is fixated on said first fixation figure; c. subsequent to b, while monitoring the second eye for refixation motion:

on said first display surface, displaying said first image of b with said first fixation figure at said location LI of said first display surface for viewing with the first eye, wherein said first fixation figure is not viewable by the second eye, and

on said second display surface, displaying a second image with a second fixation figure at a location of said second display surface for viewing with the second eye, wherein said second fixation figure is not viewable by the first eye,

wherein said locations of said first fixation figure and said second fixation figure on respective said display surfaces are the same;

wherein:

accepting as evidence that the second eye is free of ocular misalignment attributable to tropia and latent heterophoria if no said refixation movement of the second eye is observed in 'c', and

accepting as evidence that the second eye has ocular misalignment attributable to tropia and/or latent heterophoria if said refixation movement of the second eye is observed in 'c'.

16. A method for determining the magnitude and/or direction of ocular misalignment attributable to tropia and/or latent heterophoria in a subject having a first eye and a second eye, comprising:

a. concurrently:

b. subsequent to 'a',

on said first display surface, displaying a first image with a first fixation figure at a location LI of said first display surface for viewing with the first eye, wherein said first fixation figure is not viewable by the second eye, and preventing the second eye from seeing any fixation figure, for a period of time sufficient to allow the second eye to move to a rest position while the first eye is fixated on said first fixation figure; c. subsequent to 'b', while monitoring the second eye for refixation motion:

on said first display surface, displaying a first image with a first fixation figure at said location LI of said first display surface for viewing with the first eye, wherein said first fixation figure is not viewable by the second eye, and

on said second display surface, displaying a second image with a second fixation figure at a location L2 of said second display surface for viewing with the second eye, wherein said second fixation figure is not viewable by the first eye,

wherein said location of said first fixation figure LI and said location of said second fixation figure L2 on respective said display surfaces are not the same;

wherein:

if no said refixation movement of the second eye is observed in 'c,' accepting said location of said second fixation figure L2 on said second display surface as indicative of the magnitude and direction of ocular misalignment of said second eye attributable to tropia, latent heterophoria or a combination of tropia and latent heterophoria.

17. The method of claim 16, further comprising:

if said refixation movement of the second eye is observed in a preceding 'c' with a given location of said second fixation figure L2 on said second display surface, repeating 'b' and 'c' with an updated location L2 of said second fixation figure on said second display surface different from said preceding given location L2.

18. The method of any one of claims 15 to 18, wherein a 'b' and a following 'c' are performed at least two times, one of said two times where said first eye is the left eye and said second eye is the right eye, and the other of said two times where said first eye is the right eye and said second eye is the left eye.

19. The method of any one of claims 15 to 18, wherein said period of time in 'b' is not less than 6 seconds.

20. The method of any one of claims 15 to 19, wherein said preventing the first eye from seeing any fixation figure includes: blocking the view of the first eye to said first display surface.

21. The method of any one of claims 15 to 19, wherein said preventing the first eye from seeing any fixation figure includes: on said first display surface, displaying an image devoid of any fixation figure.

22. The method of any one of claims 15 to 21, wherein said display surfaces are attached to the head of the subject.

23. The method of any one of claims 15 to 21, wherein the head of the subject can move relative to said left display surface and said right display surface, and

an orientation of the head of the subject relative to said display surfaces is determined.

24. The method of any one of claims 9 to 23, wherein said concurrent displaying is simultaneous displaying said first eye image on said first display surface and said second eye image on said second display surface.

25. The method of any one of claims 9 to 23, wherein said concurrent displaying is alternately displaying said first eye image on said first display surface and said second eye image on said second display surface.

26. The method of any one of claims 9 to 25, wherein said first display surface and said second display surface are physically the same display surface.

27. The method of any one of claims 9 to 25, wherein said first display surface and said second display surface are physically different display surfaces.

28. A device useful for performing ophthalmic tests, comprising:

an image provider configured to provide image pairs for display by said display device on said display surface; and

an image obstructor wearable by a human subject that, when activated,

allows the left eye of a subject to view left eye image of an image pair displayed on said display surface while preventing the left eye from viewing a fixation figure of a corresponding right eye image displayed on said display surface; and

allows the right eye of a subject to view a right eye image of an image pair displayed on said display surface while preventing the right eye from viewing a fixation figure of a corresponding left eye image displayed on said display surface,

wherein the image provider is configured to provide:

at least one said image pair being an identical-location image pair, each image of said identical-location image pair having a single fixation figure where a location of a fixation figure of a left eye image is the same as the location of a fixation figure of a right eye image; and

at least one said image pair being a different-location image pair, each image of said different-location image pair having a single fixation figure where a location of a fixation figure of a left eye image is different from the location of a fixation figure of a right eye image.

29. The device of claim 28, wherein the image provider is configured to provide:

at least one said image pair wherein one image of said image pair has a single fixation figure and the other image of said image pair is devoid of any fixation figure.

30. The device of any one of claims 28 to 29, wherein said display device is configured to simultaneously display a left eye image and a corresponding right eye image of a said image pair.

31. The device of any one of claims 28 to 29, wherein said display device is configured to alternatingly display a left eye image and a corresponding right eye image of a said image pair.

32. The device of any one of claims 28 to 31, further comprising an eye-tracker to identify and report the gaze direction of at least one of the two eyes of a subject looking at said display surface.

33. The device of any one of claims 28 to 32, wherein said display device is configured to be attached to the head of a subject so that said display screen is at a fixed physical distance and orientation from the eyes of the subject.

34. The device of any one of claims 28 to 33, wherein:

said display device is configured to display image pairs for viewing by a subject physically located at least 30 cm from said display surface;

said image obstructor is physically located between said display surface and the eyes of a subject when worn by a subject being tested with the device; and

a left eye image and a right eye image of an image pair are displayed on the same physical said display surface.