FR3153230A1 - Method for determining at least one phoria value of a subject - Google Patents

Abstract

One aspect of the invention relates to a method for determining at least one phoria value of a subject, comprising: - displaying (530) an optotype in front of two eyes of the subject; - placing (631) a vertical dissociating prism in front of a first eye of the subject; - receiving (633) an initial vertical positioning datum comprising information describing a relative position of the two images of the optotype perceived by the subject; - placing (6341, 6351, 6361) a horizontal realignment prism in front of a second eye of the subject, the realignment prism being determined from the initial vertical positioning datum received. Figure to be published with the abstract: Figure 7

Description

Method for determining at least one phoria value of a subject TECHNICAL FIELD OF THE INVENTION

The technical field of the invention is that of optometry.

In particular, the invention relates to a method and a device for measuring at least one dissociated phoria value of a subject.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

Heterophoria is a deviation of the visual axes when both eyes are at rest. It is only evident when the vision of the two eyes is dissociated. Indeed, when the vision of the two eyes is not dissociated (binocular vision), the brain superimposes and merges the images received (one for each eye) to produce a single image.

Concretely, this means that in binocular vision, both eyes look towards the same point (in the absence of strabismus), but if one eye is masked, it deviates towards its resting position. When the eye is unmasked, it refocuses thanks to the brain's fusion reflex. This phenomenon is illustrated in Figures 1a and 1b. On the FIG. 1 , the subject fixes a target O in binocular vision and the visual axes 110, 120 of the two eyes 130, 140 are oriented towards this target O. Then, as shown in the FIG. 1 , one of the subject's eyes (on the example of the FIG. 1 , the right eye) is hidden by an object 150, for example a blackout screen. Fusion is then prevented, and the masked eye 130 takes a resting position. If the subject has heterophoria, the visual axis 160 of the masked eye 130 is offset relative to the visual axis 110 of the same eye 130 when it performs the fusion of the images. This deviation can be in the horizontal plane and/or in the vertical plane. In the example of the FIG. 1 , the deviation in the horizontal plane is represented by an angle α formed between the visual axis 160 of the masked eye 130 in the resting position and the visual axis 110 of the same eye 130 in binocular vision. This angle α represents the movement that the eye must perform to return to binocular vision during fusion. When there is no shift between the visual axes 110, 160 in the resting position and in binocular vision, we speak of orthophoria.

Heterophoria can therefore only be demonstrated when the vision of the two eyes is dissociated, in the absence of fusional stimulus (i.e. when the fusional reflex is prevented). When divergence (or convergence) also manifests itself in binocular vision, we then speak of tropia or strabismus.

Heterophoria can be vertical and/or horizontal. In the case of horizontal heterophoria, when the deviation of the visual axis is inward (toward the nose), it is called esophoria, and when the deviation of the visual axis is outward (toward the temple), it is called exophoria. In the case of vertical heterophoria, when the deviation of the visual axis is upward, it is called hyperphoria, and when the deviation of the visual axis is downward, it is called hypophoria.

Heterophoria is very common and affects approximately 75% of the population. It is not generally associated with any particular or excessive discomfort, because in the vast majority of cases, the fusion effort required to align the axes of the two eyes in binocular vision is moderate and is achieved without difficulty. However, when this effort becomes too great, and the subject does not have the necessary reserves in convergence or divergence to make the fusion effort comfortably, heterophoria can lead to eye fatigue, headaches, and even double vision problems, which require treatment with appropriate visual correction or visual training by an orthoptist to allow the subject visual comfort at all distances.

To highlight heterophoria and quantify its importance, dissociated phoria measurements are carried out. Dissociated phoria measurements are measurements carried out by dissociating the subject's binocular vision. They are expressed in prism diopters and represent the horizontal and/or vertical deviation of the visual axis of one of the subject's eyes in binocular vision compared to its resting position. In the example of Figures 1a and 1b, the horizontal phoria measurement thus represents the angle α between the visual axis 160 of an eye 130 in the resting position and the visual axis 110 of the same eye 130 when it achieves fusion (and the visual axes 110, 120 of the two eyes point towards the target O that the subject is fixing).

Equivalently, a dissociated phoria value corresponds to the prismatic deviation value of the prism that must be placed in front of the hidden eye (in the resting position) to deviate the visual axis of this eye towards the point that the other, unhidden eye is fixing.

For the sake of simplification, the "prismatic deviation value" of a prism is also called the "value" of the prism hereinafter. This value is expressed in prismatic diopters (symbol Δ). It is recalled that one prismatic diopter (1 Δ) corresponds to a deviation of one centimeter (1 cm) at a distance of one meter (1 m)

Dissociated phoria values can be measured in distance vision (VL, corresponding to a distance between the subject and the target of approximately 5 meters in France) and in near vision (VP, corresponding to a distance of approximately 40 cm in France), along the vertical axis and along the horizontal axis. For the same subject, 4 phoria values can thus be measured: horizontal phoria in VP, vertical phoria in VP, horizontal phoria in VL, vertical phoria in VL.

Dissociated phoria measurements are generally performed in an ophthalmology practice, either by the ophthalmologist himself, or by an orthoptist or a trained assistant. They can also be performed in an optical store, by an optician or an optometrist. The phoria measurements obtained are then compared to the subject's fusional reserves and the CA/A ratio in order to detect a potential binocular vision disorder, particularly convergence or divergence. Fusional reserves correspond to the convergence or divergence values that can occur without modifying accommodation or without causing diplopia. The CA/A ratio corresponds to the amount of accommodative convergence induced per diopter of accommodation, and is measured, among other things, using a so-called gradient measurement.

There are different methods for measuring dissociated phorias, including the masking-unmasking test, the Maddox test, the Thorington test, or the Von Graefe test. In all cases, phoria measurements are generally carried out on an individual with compensation (i.e., with corrective lenses). This is intended to limit the impact of accommodation on the convergence of the visual axes. Indeed, when the individual accommodates in order to see clearly, the visual axes converge. Thus, if a poorly or uncompensated individual must make an additional accommodative effort to see clearly, the measurement of dissociated phorias is impacted (more convergent or more rarely divergent) and therefore does not reflect the real angular deviation of the visual axes. This phenomenon is explained by the near vision triad (miosis, accommodation, and convergence) as well as by the desire to merge two clear images.

The masking-unmasking test involves placing a mask in front of the subject's eye, then removing the mask and observing the movement of the hidden eye. This examination does not require a refractor head and must be performed by a trained practitioner. It cannot be performed by an untrained operator. Unlike the other tests discussed below, this is an objective measure of phoria, in the sense that it does not depend on the subject's responses, but only on the practitioner's skill in assessing the deviation. For this reason, this test requires very good training to quantify heterophoria.

The Maddox test is based on the use of a cylinder (most often red), called the Maddox cylinder, which gives, from a point of light, an image in the form of a line, for example red, oriented at 90° relative to the axis of the cylinder. The subject must first fixate on a point of light, then the practitioner places the Maddox cylinder in front of one of the subject's two eyes. The subject then sees two different images: a red line (seen by the eye in front of which the cylinder is placed) and a point of light (seen by the other eye). To determine a phoria value, the practitioner passes prisms with different prismatic deviation values in front of the eye in front of which the Maddox cylinder is placed, and the prismatic deviation value of the prism for which the line and the point are aligned is determined. This prism value corresponds to the phoria value. This test must be carried out by a trained practitioner. Furthermore, the red color of the Maddox cylinder, as well as the large difference between the two images, causes poor accommodation control during the measurement, thus inducing more convergent values. This test is therefore not recommended, especially for non-presbyopic subjects.

The Thorington test requires two targets: one for distance vision and one for near vision. This test also uses a Maddox cylinder and is subject to the same drawbacks as the Maddox test. In addition, this test can only measure angular deviations up to 4 PD in distance vision, which does not allow for broad population screening.

Finally, the Von Graefe test is the most widely used subjective method for measuring phoria values in France and in a number of countries around the world. In the Von Graefe test, a so-called "dissociator" prism is placed in front of one of the subject's eyes to dissociate the subject's vision. Then, the practitioner passes prisms of different values in front of the subject's other eye, until the subject observes an alignment, on a vertical or horizontal axis, of the images. More precisely, a first prism, called a realignment prism, is placed in front of the subject's second eye. The practitioner then questions the subject about the relative positions of the images and, based on the response, determines the direction of the prismatic variation to be carried out. This method, described in more detail below with reference to the FIG. 2 , is a subjective method, which does not rely solely on the practitioner's expertise, unlike the masking-unmasking method. Furthermore, it is not subject to the existing restrictions on non-presbyopic subjects, unlike the Maddox test, and it is suitable for higher phoria values than the Thorington test. However, to be applied correctly, it requires that the practitioner be fully trained and familiar with the procedure.

As mentioned previously, the above tests are based on complex procedures comprising a series of steps that the practitioner must have in mind and apply in a well-defined order, and for which he must have been specifically trained. These constraints are an obstacle to simplified access to care and the management of visual pathologies in the population. In addition, the quality of the measurements carried out depends greatly on the experience of the practitioner, and it is complicated to obtain a very precise measurement, even for a very experienced practitioner. In addition to requiring the intervention of trained and experienced practitioners, current tests therefore suffer from a problem of reliability and reproducibility. Finally, it is noted that currently, in the Maddox, Thorington and Van Graefe tests, the practitioner must manually vary the values of the prisms that pass in front of the subject. Such manual variation is tedious for the practitioner, and represents a source of error and imprecision in the measurement of phorias.

The invention improves the situation.

The invention provides a solution to the problems mentioned above, firstly by automating the measurement of phoria (thus overcoming the problems of accuracy, repeatability and reproducibility of manual examination), and secondly by advantageously using data concerning the relative positions of the images seen by the subject after dissociation of vision, thus making it possible to determine more quickly the values of horizontal phorias of the subject and the direction of heterophoria. This point is important, because it is an unpleasant test for the patient, and the longer it is, the greater the risks of inaccuracies in the subject's responses.

One aspect of the invention thus relates to a computer-implemented method for determining at least one phoria value of a subject, the at least one phoria value comprising a horizontal phoria value, the method comprising

- control a display device to display an optotype in front of two eyes of the subject;

- controlling an automatic refractor head to place a vertical prism, called a dissociating prism, in front of a first eye among the subject's two eyes, so that the subject sees two images of the optotype respectively located on two distinct horizontal planes;

• une information traduisant si le sujet voit les deux images de l’optotype sur un même plan vertical ou sur deux plans verticaux distincts après placement du prisme dissociateur ; et
• lorsque le sujet voit les deux images de l’optotype sur deux plans verticaux distincts après placement du prisme dissociateur, une information décrivant une position relative des deux images de l’optotype perçue par le sujet ;

- déterminer, en fonction de la donnée initiale de positionnement vertical reçue, un type de prisme horizontal et une valeur initiale de déviation prismatique ;
- receive initial vertical positioning data including:

• information indicating whether the subject sees the two images of the optotype on the same vertical plane or on two separate vertical planes after placement of the dissociating prism; and
• when the subject sees the two images of the optotype on two separate vertical planes after placement of the dissociating prism, information describing a relative position of the two images of the optotype perceived by the subject;

- determine, based on the initial vertical positioning data received, a type of horizontal prism and an initial prismatic deviation value;

- controlling the automatic refractor head to place, in front of a second eye among the two eyes of the subject, the second eye being distinct from the first eye, a horizontal prism of the determined type and having a prismatic deviation value corresponding to the initial determined prismatic deviation value, the horizontal prism being called the realignment prism;

- controlling the automatic refractor head to modify the prismatic deviation value of the realignment prism until receiving alignment data indicating that the subject sees the two images of the optotype aligned in the same vertical plane;

- determine the horizontal phoria value of the subject as being the prismatic deviation value of the realignment prism upon receipt of the alignment data.

After placing the dissociating prism, the subject therefore sees two images of the optotype, one being “lower” than the other.

By "information describing a relative position of the two images of the optotype" is meant information indicating how the subject positions the two images relative to each other. In particular, such information makes it possible to indicate which image, of the top image and the bottom image, the subject sees on the right and which image the subject sees on the left.

The type of horizontal prism can be: internal base prism or external base prism.

Thus, according to the invention, the realignment prism (prism type and initial value) is determined based on how the subject sees the arrangement of the images after placement of the dissociating prism. This makes it possible to get closer, from the positioning of the realignment prism, to the horizontal phoria value of the individual. In other words, the initial value of the realignment prism is advantageously chosen to get closer, from the start, to the phoria value of the subject and thus avoid scrolling through too many prism values until alignment is obtained, unlike the Van Graefe reference test, in which the type and initial value of the realignment prism are predetermined and are the same for all subjects (generally an internal base prism of 12 to 15 Δ).

By "changing the prismatic deviation value of the realignment prism" is meant that a new realignment prism is placed in front of the subject's eye, the prismatic deviation value of which is modified compared to the prism previously placed in front of the subject's eye.

In some embodiments, the change is a gradual increase or decrease in the prismatic deviation value. For example, prismatic deviation values may be scrolled past the subject's second eye that increase (or decrease) by 0.5 Δ or 1 Δ, for example, every second (the numerical values are provided here for example purposes only).

In other embodiments, the direction of modification is not fixed. It is possible, for example, to approach the phoria value by successive modifications of the dichotomy type.

It is noted that traditionally the dissociating prism is placed in front of the right eye and the realigning prism is placed in front of the left eye, but this is not mandatory.

It is also noted that the above method can be implemented in distance vision and/or in near vision.

In one or more embodiments, the method may further comprise, prior to controlling the automatic refractor head to modify the prismatic deviation value of the realignment prism:

• une information traduisant si le sujet voit les deux images de l’optotype sur un même plan vertical ou sur deux plans verticaux distincts après placement du prisme de réalignement ; et
• lorsque le sujet voit les deux images de l’optotype sur deux plans verticaux distincts après placement du prisme de réalignement, une information décrivant une position relative des deux images de l’optotype perçue par le sujet ;

- déterminer, à partir de la nouvelle donnée de positionnement vertical, un sens de variation pour la modification de la valeur de déviation prismatique du prisme de réalignement ;
- receive new vertical positioning data including:

• information indicating whether the subject sees the two images of the optotype on the same vertical plane or on two separate vertical planes after placement of the realignment prism; and
• when the subject sees the two images of the optotype on two separate vertical planes after placement of the realignment prism, information describing a relative position of the two images of the optotype perceived by the subject;

- determine, from the new vertical positioning data, a direction of variation for the modification of the prismatic deviation value of the realignment prism;

wherein the modification of the prismatic deviation value of the realignment prism is carried out according to the determined variation direction.

Thus, according to these embodiments, the subject is asked how he perceives the positions of the images relative to each other after placement of the initial realignment prism. The direction in which the modification of the prismatic deviation value of the realignment prism takes place (increase or decrease) is then determined from the subject's response.

In one or more embodiments, the method further comprises:

- determine a type of heterophoria from a type of the realignment prism upon receipt of the alignment data.

In one or more embodiments, the at least one phoria value further comprises a vertical phoria value, and the method may further comprise:

- determining, from the determined horizontal phoria value and the determined heterophoria type, a second horizontal prism type and a second initial prismatic deviation value;

- controlling the automatic refractor head to place, in front of one of the subject's two eyes, a horizontal prism called the second dissociating prism, so that the subject sees two images of the optotype respectively located on two separate vertical planes, the second dissociating prism being of the second determined type and having a prismatic deviation value equal to the second determined initial prismatic deviation value;

- control the automatic refractor head to place, in front of the other of the subject's two eyes, a vertical prism called the second realignment prism;

- controlling the automatic refractor head to modify the prismatic deviation value of the second realignment prism until receiving a second alignment data indicating that the subject sees the two images of the optotype aligned on the same horizontal plane;

- determine the subject's vertical phoria value as the prismatic deviation value of the realignment prism upon receipt of the second alignment data.

In these embodiments, the previously determined horizontal phoria value is advantageously used to determine the vertical phoria value of the subject. More particularly, this horizontal phoria value is used to choose the type of horizontal prism and the prismatic deviation value of the dissociation prism to be placed in front of one of the subject's eyes to measure the vertical phoria value. This makes it possible to ensure adequate dissociation of the images of the optotype on two vertical planes (in particular so that these planes are neither too close together nor too far apart, which, in both cases, could impair the subject's assessment of the horizontal alignment of the images when modifying the value of the realignment prism).

In some embodiments, the first eye is a right eye, the second eye is a left eye, and the dissociating prism is a top-base prism; or the first eye is a left eye, the second eye is a right eye, and the dissociating prism is a bottom-base prism; the two images of the optotype include an image located on a lower horizontal plane and an image located on an upper horizontal plane. Determining the type of horizontal prism based on the initial vertical positioning data received includes:

- if the initial vertical positioning data received indicates that the subject sees the image of the optotype on the lower plane to the right of the image of the optotype on the upper plane, the type of horizontal prism is an external base prism;

- if the initial vertical positioning data received indicates that the subject sees the image of the optotype on the lower plane to the left of the image of the optotype on the upper plane, the type of horizontal prism is an internal base prism.

By "upper horizontal plane" and "upper horizontal plane" is meant the two distinct horizontal planes on which the two images of the optotype seen by the subject are located. By "upper horizontal plane" is meant the plane located above, and by "lower horizontal plane" is meant the plane located below. In other words, the lower horizontal plane corresponds to the plane closest to the ground and the upper horizontal plane corresponds to the plane furthest from the ground.

By "to the right of" / "to the left of" is meant a positioning of the image as perceived by the subject. For example, on the FIG. 4 , image 440 is to the right of image 430 (and image 430 is to the left of image 440).

If the initial vertical positioning data received indicates that the subject sees the image of the optotype on the lower plane to the right of the image of the optotype on the upper plane, the initial prismatic deviation value is set to a first predetermined value and the change in the prismatic deviation value of the realignment prism is an increase in the prismatic deviation value of the realignment prism.

For example, the first predetermined value can be between 0.5 Δ and 1.5 Δ.

If the initial vertical positioning data received indicates that the subject sees the optotype image on the lower plane to the left of the optotype image on the upper plane, the initial prismatic deviation value is set to a second predetermined value and changing the prismatic deviation value of the realignment prism includes:

- if the new vertical positioning data indicates that the subject sees the optotype image on the lower plane to the right of the optotype image on the upper plane, reduce the prismatic deviation value of the realignment prism;

- if the new vertical positioning data indicates that the subject sees the optotype image on the lower plane to the left of the optotype image on the upper plane, increase the prismatic deviation value of the realignment prism.

In particular, the second predetermined value may be between 7 Δ and 13 Δ.

In some embodiments, determining the horizontal prism type based on the initial vertical positioning data received may further comprise:

- if the initial vertical positioning data received indicates that the subject sees one of the two images of the optotype in an unstable position, the horizontal prism type is an internal base prism.

If the initial vertical positioning data received indicates that the subject sees one of the two images of the optotype in an unstable position, the initial prismatic deviation value is set to a third predetermined value, wherein changing the prismatic deviation value of the realignment prism comprises:

- if the new vertical positioning data indicates that the subject sees the optotype image on the lower plane to the right of the optotype image on the upper plane, reduce the prismatic deviation value of the realignment prism;

- if the new vertical positioning data indicates that the subject sees the optotype image on the lower plane to the left of the optotype image on the upper plane, increase the prismatic deviation value of the realignment prism.

By "unstable position" we mean that the subject sees one of the images "oscillate" or "shake," that is, the image is not perceived as fixed. Such a situation can occur in rather rare cases where the subject uses his fusional convergence despite the dissociation of vision.

In particular, the third predetermined value is between 3 Δ and 7 Δ in distance vision, and between 6 Δ and 10 Δ in near vision.

The above embodiments are of course not limiting, and the invention can be applied in other situations, for example when the dissociating prism is a lower base prism placed in front of the right eye or when the dissociating prism is a higher base prism placed in front of the subject's left eye.

Thus, in alternative embodiments, the first eye is a right eye, the second eye is a left eye and the dissociating prism is a lower base prism; or the first eye is a left eye, the second eye is a right eye and the dissociating prism is a higher base prism; the two images of the optotype comprise an image located on a lower horizontal plane and an image located on an upper horizontal plane. Determining the type of horizontal prism based on the initial vertical positioning data received comprises:

- if the initial vertical positioning data received indicates that the subject sees the image of the optotype on the lower plane to the right of the image of the optotype on the upper plane, the type of horizontal prism is an internal base prism;

- if the initial vertical positioning data received indicates that the subject sees the image of the optotype on the lower plane to the left of the image of the optotype on the upper plane, the horizontal prism type is an external base prism;

- if the initial vertical positioning data received indicates that the subject sees one of the two images of the optotype in an unstable position, the horizontal prism type is an internal base prism.

The predetermined values shown below can be used in a similar manner.

Another aspect of the invention relates to a device for determining at least one phoria value of a subject, the at least one phoria value comprising a horizontal phoria value, the device being configured to control a display device and an automatic refractor head, the device being configured to:

- control the display device to display an optotype in front of two eyes of the subject;

- controlling the automatic refractor head to place a vertical prism, called a dissociating prism, in front of a first eye among the subject's two eyes, so that the subject sees two images of the optotype respectively located on two distinct horizontal planes;

• une information traduisant si le sujet voit deux images de l’optotype sur un même plan vertical ou sur deux plans verticaux distincts après placement du prisme dissociateur ; et
• lorsque le sujet voit les deux images de l’optotype sur deux plans verticaux distincts après placement du prisme dissociateur, une information décrivant une position relative des deux images de l’optotype ;

- déterminer, en fonction de la donnée initiale de positionnement vertical reçue, un type de prisme horizontal et une valeur initiale de déviation prismatique ;
- receive initial vertical positioning data including:

• information indicating whether the subject sees two images of the optotype on the same vertical plane or on two separate vertical planes after placement of the dissociating prism; and
• when the subject sees the two images of the optotype on two separate vertical planes after placement of the dissociating prism, information describing a relative position of the two images of the optotype;

- determine, based on the initial vertical positioning data received, a type of horizontal prism and an initial prismatic deviation value;

- controlling the automatic refractor head to place, in front of a second eye among the two eyes of the subject, the second eye being distinct from the first eye, a horizontal prism of the determined type and having a prismatic deviation value corresponding to the initial determined prismatic deviation value, the horizontal prism being called the realignment prism;

- controlling the automatic refractor head to modify the prismatic deviation value of the realignment prism until receiving alignment data indicating that the subject sees the two images of the optotype aligned in the same vertical plane;

- determine the horizontal phoria value of the subject as being the prismatic deviation value of the realignment prism upon receipt of the alignment data.

The invention also relates to a system comprising a device as above, a display device and an automatic refractor head.

A computer program, implementing all or part of the process described above, installed on pre-existing equipment, is in itself advantageous.

Thus, the present invention also relates to a computer program comprising instructions for implementing certain steps of the computer-implemented method above, when this program is executed by a processor.

This program may use any programming language (e.g., an object-oriented language or otherwise), and may be in the form of interpretable source code, partially compiled code, or fully compiled code.

There FIG. 7 described in detail below can form the flowchart of the general algorithm of such a computer program.

The invention and its various applications will be better understood by reading the following description and examining the accompanying figures.

BRIEF DESCRIPTION OF THE FIGURES

Other features and advantages of the invention will become apparent upon reading the description, which may be read in conjunction with the figures. These figures are presented for information purposes only and in no way limit the invention.

FIG. 1 , FIG. 1 Figures 1a and 1b represent an example of heterophoria in a subject.

FIG. 2 There FIG. 2 represents an example of a flowchart representing steps implemented during a Von Graefe test according to the state of the art.

FIG. 3 , FIG. 3 , FIG. 3 , FIG. 3 Figures 3a, 3b, 3c and 3d show examples of state-of-the-art prisms.

FIG. 4 , FIG. 4 Figures 4a and 4b represent images seen by a subject during vertical and horizontal dissociation of vision, respectively.

FIG. 5 There FIG. 5 represents a system in which a method for determining a phoria measure according to one or more embodiments of the invention can be implemented.

FIG. 6 There FIG. 6 represents a flowchart of a global method for evaluating horizontal and vertical phoria measurements according to the invention.

FIG. 7 There FIG. 7 represents a flowchart of a method for determining a horizontal phoria measurement according to one or more embodiments of the invention.

FIG. 8 There FIG. 8 represents steps for determining a vertical phoria measurement according to one or more embodiments of the invention.

FIG. 9 There FIG. 9 represents a device for determining a phoria measure in one or more embodiments of the invention.

DETAILED DESCRIPTION

As mentioned above, the Von Graefe test is the most widely used subjective method in France and in several other countries around the world. It is currently used with a manual or automatic refractor head, on which the practitioner moves prisms in front of the subject's eyes. The test generally lasts between 5 and 10 minutes and can only be performed by a trained practitioner who is fully conversant with the procedure.

The Von Graefe test consists of four or five steps:

- two steps carried out in distance vision (VL, corresponding to a subject located at a distance from the target of approximately 5 m in France, 6 m in Anglo-Saxon countries): one to determine a measurement of horizontal VL phoria and one to determine a measurement of vertical VL phoria;

- two steps carried out in near vision (NP, corresponding to a subject located at a distance from the target of approximately 40 cm in France, more generally 33 cm in Anglo-Saxon countries): one to determine a measurement of horizontal NP phoria and one to determine a measurement of vertical NP phoria; and

- an additional step called “gradient measurement” carried out only on non-presbyopic subjects under 40 years old and carried out in VP.

Horizontal and vertical measurements are carried out in the same way in VP and VL. The only differences between VP and VL measurements are the distance from the subject to the target and possibly the type of target (generally, a single optotype for VL and a series of optotypes for VP).

There FIG. 2 represents an example of a flowchart of a method for measuring phorias of a subject according to the prior art, based on a Von Graefe test. More precisely, the FIG. 2 represents steps for measuring phorias in distance vision or near vision. Thus, the steps of the FIG. 2 can be implemented twice, successively: once to determine the values in distance vision, and another time to determine the values in near vision. Conventionally, the values in distance vision are determined before the values in near vision.

It is noted that the Von Graefe test is carried out while the subject is wearing the correction (or compensation) adapted to his vision (in distance vision as well as in near vision). Thus, during a step 210 (optional if the subject does not need compensation), the optimal compensation determined for the subject or the subject's usual compensation can be placed in front of the subject's eyes, in the refractor head.

In a step 220, an optotype may be displayed in front of the subject's eyes, for example an isolated letter (or an isolated symbol) or a set of letters (or symbols), such as a row or a column of letters. The optotype is located on the other side of the compensation relative to the subject's eyes. As mentioned previously, the optotype (also called a "target") is typically a single letter (or a single symbol) in distance vision and a set of letters (or a set of symbols) in near vision.

Then, the horizontal phoria value (in VP or in VL) is measured during a step 230.

To measure the horizontal phoria value (step 230), we begin by dissociating the vision (step 231), in order to allow the visual axes to assume a resting position. We then voluntarily induce double vision in the subject. The creation of artificial double vision allows the eye pair to assume its passive position (without fusional effort). To dissociate the vision, it is common to place a prism, called a dissociating prism, on one of the patient's eyes. To determine horizontal phorias, the dissociating prism is a vertical prism and induces a vertical dissociation of the vision. Traditionally, the dissociating prism is a base-upper prism placed in front of the right eye with a value equal to 6 Δ.

Figures 3a and 3b represent respectively a lower base prism and an upper base prism, which are two types of vertical prisms. It is recalled that a prism is a glass whose two surfaces (or, more broadly, the planes tangent to the two surfaces of the glass) are inclined relative to each other (i.e. form a non-zero finite angle). The thinnest part at the edge of the prism is called the "vertex", and the thickest part is called the "base". By "vertical prism", we mean a prism whose vertex-base axis is vertical (i.e. in the longitudinal axis of the patient's body, generally perpendicular to the axis passing through the centers of the patient's two eyes). A lower base prism, as represented in FIG. 3 , has its base directed downwards towards the subject's face. A prism with its upper base, as shown in FIG. 3 , with the base directed towards the top of the subject's face.

At the end of step 231, the patient's vision is vertically dissociated, and the patient sees two images of the optotype located on two separate horizontal planes. For example, when vision is dissociated by placing a top-base prism in front of the right eye and the optotype is a single letter, the subject sees two images of the optotype one above the other, as shown in FIG. 4 : a 410 image of the optotype at the top, seen by the left eye, and a 420 image of the optotype at the bottom, seen by the right eye. It is noted that on the FIG. 4 , images 410 and 420 are shown vertically aligned. However, this is not necessarily the case. Depending on the subject's horizontal phoria values, the subject may see images 410 and 420 aligned vertically, or vertically offset from each other, in one direction or the other. It is noted that the relative vertical position of the images perceived by the subject after placement of the dissociating prism is not used in the Van Graefe test.

It is noted that if a lower base prism were placed in front of the right eye, the subject would still see two images of the optotype on two separate horizontal planes, but it would be the image seen by the right eye that would be above the image seen by the left eye. Similarly, if the upper base prism had been placed in front of the subject's left eye, the image seen by the right eye would be located above the image seen by the left eye. Finally, if a lower base prism had been placed in front of the left eye, the image seen by the left eye would be located above the image seen by the right eye.

At step 233, a horizontal initial prism is placed in front of the subject's other eye (here, the left eye). Typically, the initial prism is an internal base prism having a value equal to 12 Δ.

Figures 3c and 3d represent respectively an internal base prism and an external base prism, which are two types of prisms. By "horizontal prism", we mean a prism whose vertex-base axis is horizontal (i.e. perpendicular to the longitudinal axis of the patient's body, generally in the axis passing through the centers of the patient's two eyes). In Figures 3c and 3d, the eye represented is the patient's left eye. An internal base prism, as represented in FIG. 3 , has its base directed towards the subject's nose. An external base prism, as shown in FIG. 3 , has the base directed to the other side relative to the nose (towards the temple of the side considered).

The practitioner then questions the subject about the relative vertical positions of the two images (top image and bottom image). For example, the practitioner asks the subject about the position of the bottom image relative to the top image (shifted to the right, shifted to the left, or aligned vertically). Depending on the response given (step 235), the practitioner determines the direction of the prismatic variation to be performed.

If the subject responds that the two images are not vertically aligned (exit from step 235, arrow "N"), the practitioner modifies (step 237) the prismatic deviation value of the horizontal prism (also called "realignment prism"). In the example considered (dissociating prism with upper base in front of the right eye and internal base prism in front of the left eye), if the subject sees the bottom image shifted to the left compared to the top image, the practitioner increases the prismatic deviation value of the horizontal prism. Conversely, if the subject sees the bottom image shifted to the right compared to the top image, the practitioner decreases the prismatic deviation value.

Typically, in successive steps 237, the practitioner modifies (increases or decreases) the prismatic deviation value of the horizontal prism in steps of 1 Δ.

At the end of step 237, step 235 is implemented again: the practitioner asks the patient for the relative vertical position of the two images.

If, at the end of a step 235, the subject responds that the two images are aligned vertically (exit from step 235, arrow “O”) - i.e. on the same vertical plane, as in the FIG. 4 - the test stops (step 239), and the practitioner notes the “current” value of the horizontal prism. By current value, we mean the value of the prismatic deviation of the horizontal prism used during the last performance of step 235, at the end of which the subject responded that he saw the two images aligned vertically. In other words, this current value can be (rare case) the initial value of the horizontal prism, set in step 233, or the value modified during step 237 immediately preceding a positive response from the user regarding the vertical alignment of the two images.

This current value recorded in step 239 corresponds to the value of the subject's horizontal dissociated phoria. The direction of the horizontal dissociated phoria is determined from the type of prism for which the final alignment is obtained. In the example above, if it is an internal base prism, the subject has exophoria, and if it is an external base prism, it is esophoria.

In step 240, vertical phorias are measured. To do this, we begin by horizontally dissociating the vision (step 241), by placing a horizontal dissociating prism in front of one of the subject's eyes. Typically, the dissociating prism is an internal base prism placed in front of the subject's left eye, with a value between 12 and 15 Δ.

The patient's vision is then dissociated horizontally, and the patient sees two images located on two separate vertical planes. For example, if an internal base prism is placed in front of the left eye, the subject sees two images of the optotype next to each other, as shown in FIG. 4 : a 430 image of the optotype on the left, seen by the left eye, and a 440 image of the optotype on the right, seen by the right eye. It is noted that on the FIG. 4 , images 430 and 440 are represented aligned on the same horizontal plane, but this is not necessarily the case. Depending on the subject's vertical phoria values, the subject may see images 430 and 440 aligned in the same horizontal plane, or vertically offset from each other (i.e. in two distinct horizontal planes), in one direction or the other.

If, after placing the dissociating prism in step 241, the subject sees the two images aligned on the horizontal plane, the vertical phoria value is set to zero (step 249). In other words, this corresponds to an absence of vertical phoria (which is generally expected).

Otherwise, if the subject does not see the two horizontally aligned images, a vertical realignment prism is placed in front of the subject's other eye (here, the right eye) during a step 243. This prism is typically a top or bottom base prism having a value equal to 0.5 Δ.

The practitioner then asks the subject about the horizontal alignment of the two images (left image and right image). For example, the practitioner asks the subject about the position of the left image relative to the right image (higher, lower, or horizontally aligned). Depending on the response given (step 245), the practitioner determines, if applicable, the direction of the prismatic variation to be performed.

If the subject responds that the two images are not horizontally aligned (exit from step 245, arrow “N”), the practitioner modifies (step 247) the prismatic deviation value of the realignment prism.

Typically, in successive steps 247, the practitioner modifies (increases or decreases) the prismatic deviation value of the vertical prism in steps of 0.5 Δ.

At the end of step 247, step 245 is implemented again: the practitioner asks the subject how the images are located relative to each other in horizontal planes.

If, at the end of a step 245, the subject responds that the two images are aligned horizontally (exit from step 245, arrow “O”), the test stops (step 249), and the practitioner notes the “current” value of the realignment prism, i.e. the value of the realignment prism at the last time step 245 was performed, at the end of which the subject responded that he saw the two images aligned horizontally. In other words, this current value can be the initial value of the vertical prism, set at step 243, or the value modified at step 247 immediately preceding a positive response from the user regarding the horizontal alignment of the two images.

This current value recorded in step 249 corresponds to the value of the subject's vertical dissociated phoria (in VL or VP). The direction of the vertical dissociated phoria can be determined from the type of realignment prism for which the alignment is obtained.

In the non-presbyopic subject, an additional step not shown on the FIG. 2 can be implemented, only in near vision: the gradient measurement. This additional step makes it possible to determine the link between accommodative convergence and accommodation (CA/A ratio). This method determines the impact of accommodation on the convergence of the visual axes. This allows the practitioner to determine the appropriate treatment for the subject (wearing an addition, rehabilitation, adding prisms, etc.). To determine the gradient, a second measurement of horizontal dissociated phorias is carried out in near vision only, with the addition, on both eyes, of a +1.00 diopter lens to the distance vision correction. The practitioner ensures beforehand that the addition of this +1.00 diopter lens does not cause blurred vision in the subject. The gradient measurement is known from the state of the art and is not detailed further here.

It appears from the above description that the Van Graefe test is delicate and laborious to implement. For each phoria measurement, the practitioner must manually place the dissociating prism on one eye, place a realignment prism on the other eye, question the subject on the relative position of the images, and interpret the subject's response to determine in which direction the prismatic variation should be carried out (increase or decrease the value of the realignment prism, which requires continual gymnastics since the subject's perception is inverted in relation to the prisms that must be introduced). Then, the practitioner must manually vary the values of the realignment prism, which in itself constitutes an obstacle to a precise determination of the value of the measurement (it is not easy to precisely modify the values of the realignment prism with the refraction heads, especially when they are manual).

Since these steps are repeated to perform the vertical and horizontal measurements, in VP and VL, the number of manipulations and the risk of error in the correct interpretation of the subject's responses make this test a long and tedious method for the practitioner, as well as for the subject. In addition, the practitioner must determine, from the relative positions of the letters indicated by the subject, the direction of the heterophoria, which can lead to inversions. Finally, the variation of the prisms on a manual refraction head is done using a wheel. The accuracy of the measurement can therefore be impacted by the variation of the prisms, which can be less regular, and by the time, which can be extended. The practitioner's reaction time also impacts this accuracy.

These constraints constitute an obstacle to systematic monitoring of binocular vision, which is often neglected at present when a subject comes for eye examinations.

Furthermore, the Von Graefe test is a dissociative test known to induce fusional convergence, due to the significant duration of the measurement. For example, as mentioned previously, to measure horizontal phoria values, we start with a dissociative prism with an internal base of 12 Δ. Assuming a prismatic variation of 1 Δ per second, as the expected average phoria is typically 3 Δ in exophoria, the measurement takes on average 9 seconds until alignment, which is sufficient to induce fusional convergence. This is the cause of instability in the measurements, reflected by a large variability in the measurements obtained for the same subject by a single practitioner (lack of repeatability) or several practitioners (lack of reproducibility).

To overcome the above problems, the invention first proposes to automate the phoria measurements, using an automatic refractor head controlled by a control device. The control device comprises a control module configured to send control signals to the automatic refractor head. The control device may comprise or be connected to a selection screen (for example a screen connected to an input device, such as a mouse and/or a keyboard, or a touch screen) configured to display proposals to a user and to receive at least one selection of at least one of the displayed proposals. Upon receiving a control signal, the automatic refractor head is configured to place at least one prism in front of an eye of the subject. The automatic refractor head comprises two locations, each location corresponding to a respective eye, capable of receiving prisms.

For example, a control signal may include:

- a first data indicating in front of which eye the prism must be placed (i.e. in which location of the refractor head the prism must be placed);

- a second data item corresponding to the type (internal base, external base, lower base or upper base) of the prism to be placed;

- a third data corresponding to the prismatic deviation value of the prism to be placed.

Upon receipt of such a control signal, the refractor head places, in the location associated with the first data item, a prism of the type indicated by the second data item and having a value indicated by the third data item.

The example above is for a control signal to control the placement of a single prism. The control signal can also control successive placements of prisms.

For example, the control signal may include a field indicating whether it concerns the placement of a single prism or successive prisms, and, if it concerns the placement of successive prisms, additional fields including a fourth data item corresponding to the direction of prismatic variation (scrolling in the increasing or decreasing direction of the prismatic deviation values), a fifth data item corresponding to the step (i.e. the difference, in prismatic diopters, between two successive prism values) and a sixth data item corresponding to the frequency of change (i.e. the duration between two successive prism placements). These fields may be set by default to predefined values, for example 1 Δ and 1 second, which are modified only if the control signal includes other values.

To control a scrolling of realignment prisms having successive prismatic deviation values (increasing or decreasing), the realignment module can: either send a single control signal to control the successive placement of the prisms (as in the second case above), or send several control signals successively, each control signal controlling the placement of a single prism (as in the first case above). In the latter case, the control signals can be sent by the control module to the automatic refractor head with a predefined frequency and step

Furthermore, the invention proposes to determine the initial realignment prism as a function of the relative position of the optotypes perceived by the subject after placement of the dissociating prism. Once the dissociating prism is placed in front of one eye of the subject (step 231 of the FIG. 2 ), the subject is asked about the relative position of the optotypes he observes when the dissociating prism is placed in front of one of his eyes, then an initial realignment prism whose value depends on his response is placed in front of the subject's other eye. In contrast, in the Van Graefe test, the initial realignment prism has a predetermined type and value, which are therefore the same for all subjects.

The horizontal phoria measurement is thus obtained more quickly, because the initial information on the vertical shift between the two images without a realignment prism (with only the dissociating prism) is advantageously used to automatically frame the horizontal phoria value. This makes it possible to test a much smaller number of realignment prisms than with a test carried out manually using the classic method.

There FIG. 5 represents an example system in which a phoria measurement evaluation method according to one or more embodiments of the invention can be implemented.

The system of the FIG. 5 includes a control device (or control device) 510 including a control module configured to control an automatic refractor head. In the example of the FIG. 5 , the control device 510 is connected to a selection screen of a user equipment 540, which here is in the form of a tablet. The control device 510 is configured to control a display on this selection screen and receive selection data from the selection screen. In this example, the control device 510 has the form of a connection “box” making it possible to link different equipment dedicated to visual examinations. Of course, other embodiments are conceivable. In particular, the control device 510 may comprise the selection screen. In certain embodiments, the selection screen may be replaced by any other system for selecting and receiving instructions (for example a screen and a mouse/joystick/touchpad, or a screen and a voice recognition system).

The system of the FIG. 5 further comprises an automatic refractor head 520 configured to place optical lenses and/or prisms in front of a subject's eyes. The refractor head 520 comprises two locations corresponding respectively to the two eyes of the subject. The controller 510 is connected to the automatic refractor head 520 and configured to control the placement of lenses or prisms in each location of the automatic refractor head 520.

The system may also include a display means 530 (e.g., a screen). The control device 510 may be connected to the display means 530 and configured to control a display of data on the selection means 530. For example, the control device 510 may control the display of an optotype on the display means 530.

The connection between the control device 510 and the automatic refractor head 520 and/or between the control device 510 and the display means 530 and/or between the control device 510 and the user equipment 540 may be wired or wireless.

There FIG. 6 represents an overall flowchart of a method for measuring phorias of a subject according to embodiments of the invention. Similar to the Van Graefe test represented in FIG. 2 , the method according to the invention comprises, in embodiments:

- an optional step 610 during which a compensation is placed in front of the subject's eyes, in the refractor head (in a similar manner to step 210 of the Van Graefe test). Indeed, as in the Van Graefe test, it is preferable to measure the subject's phoria values when the subject is wearing his optimal compensation;

- a step 620 during which an optotype is displayed in front of the subject's eyes (similarly to step 220 of the Van Graefe test);

- a step 630 during which the horizontal phoria value of the subject (in VP or in VL) is determined; and

- a step 640 during which the vertical phoria value of the subject (in VP or in VL) is determined.

It is customary to first measure the horizontal phoria and then measure the vertical phoria, but this is not mandatory. Thus, in embodiments, step 630 may be implemented after step 640 (except in embodiments of the FIG. 8 , in which the horizontal phoria measure is used to determine the vertical phoria measure).

It is also noted that the process of the FIG. 6 allows the evaluation of phoria values in VP or VL. Only the distance between the subject and the target, and possibly the type of target, differs between the measurement in VP and the measurement in VL. Thus, the method of the FIG. 6 can be implemented firstly in VL, then in VP (or vice versa). Step 610 can be shared (the same compensation is placed in front of the subject's eyes for both series of measurements).

It appears from the FIG. 6 that the method according to the invention remains, in its overall implementation, similar to that of the FIG. 2 . As described below, it is the implementations of step 630, and possibly step 640, that differ from the Van Graefe test.

There FIG. 7 represents sub-steps of step 630 of determining the horizontal phoria value of a subject according to an embodiment of the invention.

It is assumed that an optotype is placed in front of the subject's eyes. Optionally, the optotype may be placed after step 631.

In a first step 631, the subject's vision is dissociated, by controlling the refractor head to place, in front of a first eye of the subject, a vertical dissociating prism. In the example described here with reference to the FIG. 6 , it is assumed that, in step 631, a top-base prism is placed in front of the subject's right eye. It is noted that, in other embodiments, it is possible to use a bottom-base prism and/or to place the dissociating prism in front of the left eye.

For example, the prism (called a "dissociating prism") used to dissociate vision in step 631 may have a value equal to 6 Δ. Other values are possible, for example values between 3 and 12 Δ.

At the end of step 631, the subject therefore sees two images of the target, one below the other. As mentioned above, the two images of the target may be offset (according to the subject's perception) vertically relative to each other (i.e. the images are located on two separate vertical planes). Unlike the Van Graefe test, in the method of the FIG. 6 , the initial realignment prism is selected based on how the subject sees the target images, which means that the initial realignment prism is, by default, more suited to the subject's phoria value. The horizontal phoria measurement is thus obtained more quickly.

Thus, in step 633, the subject is asked how he sees the two images in relation to each other: vertically aligned or vertically offset and, in this case, which image is to the right (or left) of the other. For example, the practitioner may ask the subject the following question: "Is the bottom letter to the right, left, or below the top letter?" He may also ask him if the bottom letter is "unstable", that is, does it oscillate around a position.

If the subject sees the bottom image to the right of the top image, an external base prism having for example a value equal to 0.5 Δ is placed in front of the subject's left eye (step 6341). As long as the subject does not indicate that the images are aligned vertically (therefore as long as no stop data is sent to the control device), the value of the external base prism is increased. Thus, as long as in step 6342 no stop data is received by the control device, the value of the realignment prism is increased (step 6343). If, during an iteration of step 6342, stop data is received (which indicates that the subject sees the images aligned vertically), the refractor head stops scrolling the realignment prisms, the current value of the realignment prism is recorded as the subject's horizontal phoria value (step 639).

If the subject sees the bottom image to the left of the top image, an inner base prism is placed in front of the subject's left eye (step 6351). For example, this inner base prism can have an initial value between 7 Δ and 13 Δ. The subject is then asked, in step 6352, how they see the images relative to each other in the vertical plane.

If the subject sees the two images aligned vertically, the initial value of the internal base realignment prism is recorded as the subject's horizontal phoria value (step 639).

If the subject sees the bottom image to the right of the top image, the value of the internal base prism is decreased (step 6353). By "the value of the prism is decreased (or increased)", it is understood that the refractor head scrolls, in front of the subject's left eye, prisms whose successive values are decreasing (or increasing). In step 6354, it is checked whether a stop data item is received, and, as long as this is not the case, the value of the prism is decreased (step 6353). If, at the end of an iteration of step 6354, a stop data item is received by the control device (which indicates that the subject sees the images aligned vertically), the refractor head stops scrolling the realignment prisms, the current value of the realignment prism is recorded as the horizontal phoria value of the subject (step 639).

If the subject sees the bottom image to the left of the top image, the value of the internal base prism is increased (step 6355).

In step 6356, it is checked whether a stop data is received, and, as long as this is not the case, the value of the prism is increased (step 6355). If, at the end of an iteration of step 6356, a stop data is received by the control device (which indicates that the subject sees the images aligned vertically), the refractor head stops scrolling the realignment prisms, the current value of the realignment prism is recorded as the horizontal phoria value of the subject (step 639).

If the subject sees the bottom image unstable, a step 6361 is implemented, during which an inner base prism is placed in front of the subject's left eye. For example, this inner base prism can have an initial value between 3 Δ and 7 Δ for distance vision, and between 6 Δ and 10 Δ for near vision.

It is noted that step 6361 may also be implemented when the subject sees the bottom image aligned with the top image. Indeed, in such a situation, one possibility is that the subject does not exhibit horizontal heterophoria. It may be preferable, however, to confirm this by deliberately shifting the image using a realignment prism, then decreasing its value, to confirm the absence of horizontal heterophoria.

The subject is then asked, at step 6362, how he or she sees the images relative to each other in the vertical plane.

If the subject sees the two images aligned vertically, the initial value of the realignment prism is recorded as the subject's horizontal phoria value (step 639).

If the subject sees the bottom image to the right of the top image, the value of the internal base prism is decreased (step 6363) until no stop data is received (step 6364). If, at the end of an iteration of step 6364, a stop data is received (reflecting the fact that the subject sees the images aligned vertically), the refractor head stops scrolling the realignment prisms, the current value of the realignment prism is recorded as the subject's horizontal phoria value (step 639).

If the subject sees the bottom image to the left of the top image, the value of the internal base prism is increased (step 6365) as long as no stop data is received (step 6366). If, at the end of an iteration of step 6366, a stop data is received (reflecting the fact that the subject sees the images aligned vertically), the refractor head stops scrolling the realignment prisms, the current value of the realignment prism is recorded as the subject's horizontal phoria value (step 639).

In step 639, the type of heterophoria (exophoria or esophoria) is also determined, based on the type of horizontal prism (internal or external base) that made it possible to obtain the alignment. In the previous example, if the last realignment prism placed is an external base prism, it is an esophoria, and if the last realignment prism placed is an internal base prism, it is an exophoria.

In steps 6343, 6353, 6355, 6363 and 6365 above, successive realignment prisms may be placed in front of the subject's left eye with a predefined pitch and frequency (e.g. an increase/decrease of 0.5 Δ or 1 Δ every second).

Of course, steps 6342 and 6343, 6353 to 6356 and 6363 to 6366 above correspond to particular implementations of the method, but the invention is not limited to such implementations. For example, when the prism values are successively increased or decreased, the step between two successive values is not necessarily constant. For example, the differences between two successive values of the prism can decrease over the iterations (to converge more quickly towards an approximate value, then adjust the value more finely).

The wording "changing the value of the realignment prism" is used for simplicity, and should be interpreted as placing a new realignment prism with a different value than the previous one in front of the subject's eye.

Thanks to the process described above with reference to the FIG. 7 , the horizontal phoria measurement is obtained more quickly, because the initial information on the vertical shift between the two images without realignment prism (with only the dissociating prism) is advantageously used to automatically frame the horizontal phoria value. This allows testing a much smaller number of realignment prisms than with the Van Graefe test.

In an example of implementation of the method of the FIG. 7 , the practitioner can interact with the device 510 (via a human-machine interface, such as a touch screen, a keyboard, a mouse, a control button, a voice control module, etc.) to indicate that he wishes to start a phoria measurement examination (command to start the measurement). He can also send to the device 510 the subject's compensation values. Alternatively, the device 510 can retrieve this data from a database for example. Upon receipt of a command to validate the compensation values, the device can command the automatic refractor head 520 so that glasses corresponding to the subject's compensation are placed in front of the subject's eyes. Upon receipt of a command to start the measurement, the device 510 can send a command to the automatic refractor head to place a dissociating prism in front of a first eye of the subject (step 631).

The device 510 can then command the display of a question to the subject (step 633). For example, the question may be “how is the bottom letter positioned relative to the top letter?”. It is noted that the display of data on a screen can be replaced or supplemented by the reading, on a loudspeaker of a voice module connected to the device 510, of corresponding questions or instructions.

The device 510 may control the display of a plurality of selections, for example: “left”, “right”, “aligned” and “unstable”. The practitioner then enters the subject’s response into the device 510, via the human-machine interface of the device 510. For example, the practitioner may place their finger on an area of a touch screen corresponding to the response provided by the subject. Upon receipt of this information, the device 510 sends the automatic refractor head 520 a control signal to place in front of the subject’s second eye one of the realignment prisms of steps 6341, 6351 and 6361. The other steps of the FIG. 7 can be implemented in a similar manner. At the end of step 639, the measurement result can be displayed on a screen of the device 510.

In some embodiments, the vertical phoria value (step 640 of the FIG. 6 ) can be determined in a similar way to the Van Graefe test (step 240 of the FIG. 2 ), in an automated manner. Indeed, the vertical phoria value is generally less important than the horizontal phoria value, which means that the number of prisms to be tested is less important than for determining the horizontal phoria value.

In alternative embodiments, the horizontal phoria value can be advantageously used in determining the vertical phoria value, so that the dissociating prism for dissociating the subject's vision and shifting the images horizontally actually produces the expected effect. Indeed, if a dissociating prism having a value that corresponds to (or is sufficiently close to) the horizontal phoria value of the subject is placed, the images will not be (or will be only slightly) shifted horizontally relative to each other. In addition, this makes it possible to deliberately shift the image seen by one eye in a given direction (for example the image of the right eye to the right of that of the left eye), to be sure to place the realignment prism in the correct direction to obtain alignment. In these embodiments, step 640 of the FIG. 6 is necessarily implemented after step 630.

An example of such an embodiment is shown in FIG. 8 .

In step 810, the value of the dissociating prism(s) to be placed in front of an eye(s) of the subject is determined, and the dissociating prism(s) are placed in front of the eye(s) of the subject.

For example, the dissociating prism can be an internal base prism with a value equal to the horizontal phoria value increased by a predetermined amount, for example 3 Δ. Alternatively, it is possible to associate prism values with predetermined value intervals. When the horizontal phoria value is too high, two internal base dissociating prisms can be placed in front of the subject's eyes (one prism in front of each eye). Optionally, it can also be decided that beyond a certain horizontal phoria value, the vertical phoria value is not determined (in particular for material reasons, because there are no longer prisms strong enough to dissociate vision).

For example :

- If the subject presents esophoria, or if he presents exophoria with a value less than or equal to 7 Δ, an internal base dissociating prism with a value greater than 8 Δ in distance vision or greater than 10 Δ in near vision is placed in front of the subject's left eye;

- If the subject presents an exophoria with a value strictly greater than 7 Δ and less than or equal to 12 Δ, an internal base dissociating prism between 13 Δ and 18 Δ in distance vision / between 15 Δ and 25 Δ in near vision is placed in front of the subject's left eye;

- If the subject presents an exophoria with a value strictly greater than 12 Δ and less than or equal to 20 Δ, an internal base dissociating prism with a value greater than 18 Δ is placed in front of the subject's left eye and an internal base dissociating prism between 3 Δ and 8 Δ in distance vision / between 5 Δ and 10 Δ in near vision is placed in front of the subject's right eye; and

- If the subject presents an exophoria with a value strictly greater than 20 Δ, no vertical phoria measurement is carried out.

Of course, the number of intervals above and the values of the terminals and prisms are provided as examples and are not limiting.

At the end of step 810, the subject's vision is dissociated on the horizontal plane (they see one image lower than the other). At step 820, the subject is asked how they see the images in relation to each other. For example, the practitioner may ask: "Is the letter on the left above, below, or on the same line as the letter on the right?"

If the subject sees both images on the same line (horizontal alignment), the vertical phoria value is zero (step 830).

If the subject sees the left image lower than the right image, a base-up realignment prism is placed in front of the subject's right eye (step 840). For example, this base-up realignment prism has an initial value of 0.5 Δ. As long as no stop data is received (test 850), i.e., as long as the subject sees the left image lower than the right image, the value of the base-up realignment prism is increased (step 840), for example by 0.5 Δ per second. Upon receipt of stop data (test 850) indicating that the subject sees the two images aligned horizontally (i.e., one next to the other, at the same level), the current value of the base-up realignment prism is recorded as the stop value (step 830), and the type of vertical heterophoria is a L/R hyperphoria (left over right).

If the subject sees the left image higher than the right image, a base-down realignment prism is placed in front of the subject's right eye (step 860). For example, this base-down realignment prism has an initial value of 0.5 Δ. As long as no stop data is received (test 870), i.e., as long as the subject sees the left image higher than the right image, the value of the base-down realignment prism is increased (step 860), for example, by 0.5 Δ per second. Upon receipt of stop data (test 870) indicating that the subject sees the two images aligned horizontally (i.e., one next to the other, at the same level), the current value of the base-down realignment prism is recorded as the stop value (step 830), and the type of vertical heterophoria is a R/L hyperphoria (right over left).

As mentioned previously, steps 630 and 640 of horizontal and vertical phoria measurements can be implemented in distance vision (VL) and near vision (VP).

Between the two types of examination (VL and VP), there are certain parameters that can be modified. For example, the distance between the subject and the target differs depending on whether the examination is in VL or VP.

In some embodiments, the subject's compensation may also differ in VL and VP. For example, in VL, the subject may wear VL compensation regardless of age. In VP, a distinction may be made between a presbyopic subject and a non-presbyopic subject: the presbyopic subject is corrected by their VP compensation, while the non-presbyopic subject is corrected by their VL compensation.

The values of the prisms may also differ depending on whether the examination is in VL or VP. For example, for determining the horizontal phoria value, the initial (predetermined) value of the internal base prism of step 6361 may be higher in VL than in VP. For determining the vertical phoria value, the value of the dissociating prism(s) placed in front of the subject's eye(s) may be higher in VP than in VL.

Figures 6 to 8 above have been described in the case where the dissociating prism is placed in front of the subject's right eye, and the realigning prism is placed in front of the subject's left eye. It is noted that, while it is customary to proceed in this way in the Van Graefe test, it is not mandatory. The invention also applies when the dissociating prism is placed in front of the left eye and the realigning prism is placed in front of the right eye.

Figures 6 to 8 above have also been described in the case where the dissociating prism is a top-base prism (for horizontal phorias) or an internal base prism (for vertical phorias). The invention also applies when the dissociating prism is a bottom-base prism (for horizontal phorias) or an external base prism (for vertical phorias) – even if the latter case is not preferred, because it is quite difficult, due to the fact that the subjects generally have convergence capacities clearly superior to divergence capacities, to obtain a dissociation with an external-base prism.

There FIG. 9 represents an example of a device 510 making it possible to implement at least certain steps of the method for determining phorias of the invention, according to one or more embodiments of the invention.

In these embodiments, the device 510 comprises a control module 900, comprising a memory 901 for storing instructions allowing the implementation of the methods and temporary data for carrying out different steps of the methods described previously.

The control module 900 further comprises a circuit 902. This circuit may be, for example, a processor capable of interpreting instructions in the form of a computer program, an electronic card whose steps of the method of the invention are described in the silicon, or even a programmable electronic chip such as an FPGA chip (for “Field-Programmable Gate Array” in English).

The control module 900 comprises an input interface 903 for receiving input data, and an output interface 904 for providing one or more phoria values. The input data may be, for example, measurement start data, instructions corresponding to proposition selections (for example a selection of a validation proposition or a selection of a value proposition).

The control module 900 may also include a communication module 905 configured to communicate with one or more devices, including the automatic refractor head.

Of course, the present invention is not limited to the embodiments described above as examples. It extends to other variants.

Claims (15)

A computer-implemented method of determining at least one phoria value of a subject, the at least one phoria value comprising a horizontal phoria value, the method comprising:
- controlling a display device (530) to display an optotype in front of two eyes of the subject;
- controlling (631) an automatic refractor head (520) to place a vertical prism, called a dissociating prism, in front of a first eye among the two eyes of the subject, so that the subject sees two images of the optotype respectively located on two distinct horizontal planes;
- receive (633) initial vertical positioning data comprising:

• information indicating whether the subject sees the two images of the optotype on the same vertical plane or on two separate vertical planes after placement of the dissociating prism; and
• when the subject sees the two images of the optotype on two separate vertical planes after placement of the dissociating prism, information describing a relative position of the two images of the optotype perceived by the subject;

- determine, based on the initial vertical positioning data received, a type of horizontal prism and an initial prismatic deviation value;
- controlling the automatic refractor head to place (6341, 6351, 6361), in front of a second eye among the two eyes of the subject, the second eye being distinct from the first eye, a horizontal prism of the determined type and having a prismatic deviation value corresponding to the initial determined prismatic deviation value, the horizontal prism being called a realignment prism;
- controlling the automatic refractor head to modify (6343, 6353, 6355, 6363, 6365) the prismatic deviation value of the realignment prism until receiving (6342, 6354, 6356, 6364, 6366) alignment data indicating that the subject sees the two images of the optotype aligned in the same vertical plane;
- determining (639) the horizontal phoria value of the subject as being the prismatic deviation value of the realignment prism upon receipt (6342, 6354, 6356, 6364, 6366) of the alignment data. The method of claim 1, further comprising, before controlling the automatic refractor head to modify the prismatic deviation value of the realignment prism:
- receive (6352, 6362) new vertical positioning data comprising:

• information indicating whether the subject sees the two images of the optotype on the same vertical plane or on two separate vertical planes after placement of the realignment prism; and
• when the subject sees the two images of the optotype on two separate vertical planes after placement of the realignment prism, information describing a relative position of the two images of the optotype perceived by the subject;

- determine, from the new vertical positioning data, a direction of variation for the modification of the prismatic deviation value of the realignment prism;
wherein the modification (6353, 6355, 6363, 6365) of the prismatic deviation value of the realignment prism is carried out according to the determined variation direction. Method according to one of the preceding claims, further comprising:
- determine a type of heterophoria from a type of the realignment prism upon receipt of the alignment data. The method of claim 3, wherein the at least one phoria value further comprises a vertical phoria value, the method comprising:
- determining, from the determined horizontal phoria value and the determined heterophoria type, a second horizontal prism type and a second initial prismatic deviation value;
- controlling (810) the automatic refractor head (520) to place, in front of one of the subject's two eyes, a horizontal prism called the second dissociating prism, so that the subject sees two images of the optotype respectively located on two distinct vertical planes, the second dissociating prism being of the second determined type and having a prismatic deviation value equal to the second determined initial prismatic deviation value;
- control the automatic refractor head to place (840, 860), in front of the other of the subject's two eyes, a vertical prism called the second realignment prism;
- controlling the automatic refractor head to modify the prismatic deviation value of the second realignment prism until receiving (850, 870) a second alignment data indicating that the subject sees the two images of the optotype aligned on the same horizontal plane;
- determining (830) the vertical phoria value of the subject as being the prismatic deviation value of the realignment prism upon receipt of the second alignment data. Method according to one of the preceding claims, in which:
the first eye is a right eye, the second eye is a left eye, and the dissociating prism is a top-base prism; or
the first eye is a left eye, the second eye is a right eye and the dissociating prism is a lower base prism;
wherein the two images of the optotype comprise an image located on a lower horizontal plane and an image located on an upper horizontal plane;
wherein determining the type of horizontal prism based on the initial vertical positioning data received comprises:
- if the initial vertical positioning data received indicates that the subject sees the image of the optotype on the lower plane to the right of the image of the optotype on the upper plane, the type of horizontal prism is an external base prism;
- if the initial vertical positioning data received indicates that the subject sees the optotype image on the lower plane to the left of the optotype image on the upper plane, the horizontal prism type is an internal base prism. The method of claim 5, wherein the initial vertical positioning data received indicates that the subject sees the optotype image on the lower plane to the right of the optotype image on the upper plane, wherein the initial prismatic deviation value is set to a first predetermined value, and wherein the change (6343) in the prismatic deviation value of the realignment prism is an increase in the prismatic deviation value of the realignment prism. Method according to the preceding claim, in which the first predetermined value is between 0.5 Δ and 1.5 Δ. The method of claim 5 in combination with claim 2, wherein the initial vertical positioning data received indicates that the subject sees the optotype image on the lower plane to the left of the optotype image on the upper plane, wherein the initial prismatic deviation value is set to a second predetermined value, wherein changing the prismatic deviation value of the realignment prism comprises:
- if the new vertical positioning data indicates that the subject sees the image of the optotype on the lower plane to the right of the image of the optotype on the upper plane, decrease (6353) the prismatic deviation value of the realignment prism;
- if the new vertical positioning data translates that the subject sees the image of the optotype on the lower plane to the left of the image of the optotype on the upper plane, increase (6355) the prismatic deviation value of the realignment prism. Method according to the preceding claim, in which the second predetermined value is between 7 Δ and 13 Δ. The method of claim 5, wherein determining the horizontal prism type based on the initial vertical positioning data received further comprises:
- if the initial vertical positioning data received indicates that the subject sees one of the two images of the optotype in an unstable position, the horizontal prism type is an internal base prism. The method of claim 10, wherein the initial vertical positioning data received indicates that the subject is viewing one of the two images of the optotype in an unstable position, wherein the initial prismatic deviation value is set to a third predetermined value, wherein changing the prismatic deviation value of the realignment prism comprises:
- if the new vertical positioning data indicates that the subject sees the image of the optotype on the lower plane to the right of the image of the optotype on the upper plane, decrease (6363) the prismatic deviation value of the realignment prism;
- if the new vertical positioning data translates that the subject sees the image of the optotype on the lower plane to the left of the image of the optotype on the upper plane, increase (6365) the prismatic deviation value of the realignment prism. Method according to claim 11, wherein the third predetermined value is between 3 Δ and 7 Δ in distance vision, and between 6 Δ and 10 Δ in near vision. Device (510) for determining at least one phoria value of a subject, the at least one phoria value comprising a horizontal phoria value, the device being configured to control a display device (530) and an automatic refractor head (520), the device (510) being configured to:
- controlling (530) the display device to display an optotype in front of two eyes of the subject;
- controlling (631) the automatic refractor head to place a vertical prism, called a dissociating prism, in front of a first eye among the two eyes of the subject, so that the subject sees two images of the optotype respectively located on two distinct horizontal planes;
- receive (633) initial vertical positioning data comprising:

• information indicating whether the subject sees the two images of the optotype on the same vertical plane or on two separate vertical planes after placement of the dissociating prism; and
• when the subject sees the two images of the optotype on two separate vertical planes after placement of the dissociating prism, information describing a relative position of the two images of the optotype perceived by the subject;

- determine, based on the initial vertical positioning data received, a type of horizontal prism and an initial prismatic deviation value;
- controlling (6341, 6351, 6361) the automatic refractor head to place, in front of a second eye among the two eyes of the subject, the second eye being distinct from the first eye, a horizontal prism of the determined type and having a prismatic deviation value corresponding to the initial determined prismatic deviation value, the horizontal prism being called a realignment prism;
- controlling the automatic refractor head to modify (6343, 6353, 6355, 6363, 6365) the prismatic deviation value of the realignment prism until receiving (6342, 6354, 6356, 6364, 6366) alignment data indicating that the subject sees the two images of the optotype aligned in the same vertical plane;
- determining (639) the horizontal phoria value of the subject as being the prismatic deviation value of the realignment prism upon receipt (6342, 6354, 6356, 6364, 6366) of the alignment data. A system comprising a device (510) according to claim 14, a display device (530) and an automatic refractor head (520). Computer program product comprising instructions for implementing the method according to one of claims 1 to 12 when this program is executed by a processor.