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WO2004089199A1 - Test de l'acuité visuelle - Google Patents

Test de l'acuité visuelle Download PDF

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Publication number
WO2004089199A1
WO2004089199A1 PCT/GB2004/001581 GB2004001581W WO2004089199A1 WO 2004089199 A1 WO2004089199 A1 WO 2004089199A1 GB 2004001581 W GB2004001581 W GB 2004001581W WO 2004089199 A1 WO2004089199 A1 WO 2004089199A1
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WO
WIPO (PCT)
Prior art keywords
displayed
subject
symbols
symbol
visual acuity
Prior art date
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Ceased
Application number
PCT/GB2004/001581
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English (en)
Inventor
Robert L. Johnston
Nigel Davies
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Clement Clarke International Ltd
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Clement Clarke International Ltd
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Filing date
Publication date
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Publication of WO2004089199A1 publication Critical patent/WO2004089199A1/fr
Anticipated expiration legal-status Critical
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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/02—Subjective types, i.e. testing apparatus requiring the active assistance of the patient
    • A61B3/028—Subjective types, i.e. testing apparatus requiring the active assistance of the patient for testing visual acuity; for determination of refraction, e.g. phoropters
    • A61B3/032—Devices for presenting test symbols or characters, e.g. test chart projectors

Definitions

  • the present invention relates to visual function assessment such as visual acuity testing. Such tests can be useful in a determination of the condition of the sight of a subject.
  • a known method for performing visual function assessment is letter recognition visual acuity testing.
  • a chart displaying letters (or, more generally, symbols) of decreasing size is located a known distance from a subject. The subject reads out the letters on the chart until a letter size is reached which cannot be recognised by the subject.
  • Known charts include the Snellen chart, introduced in 1862. This was superseded by the logMAR (logarithmic Minimum Angle of Resolution) chart, developed in 1976.
  • the minimum angle of resolution is the smallest angular separation of two objects of image features that can be resolved by the visual system. This is therefore a measure of the finest spatial detail that the visual system can interpret.
  • Each of these charts displays letters for attempted identification by the subject.
  • the number of letters of different size contained on the chart is dependent on the size of the letters, the size of the chart and the size difference between letters of different size.
  • known charts display a wide range of letter sizes. To allow this, it is necessary that the increment between letter sizes is relatively large.
  • known tests give a relatively low resolution for the threshold of visual acuity. For example, typical known tests give a resolution of about 0.1 log units per decrease in letter size .
  • the displayed size of each symbol is selected from a substantially continuous range of selectable symbol sizes.
  • the invention can therefore allow a selection of the selectable symbol sizes to be displayed, i.e. not all of the selectable symbol sizes need be displayed. This in turn allows the selection of only those symbol sizes which will be of use in an assessment of visual function of a particular subject.
  • the decrease in symbol size between subsequent displayed symbols can be made very small, as desired. This can assist in increasing the resolution of the assessment.
  • the range of selectable symbol sizes is not absolutely continuous. In other words, the number of selectable symbol sizes may not be infinite. Rather, it is preferred that the range of selectable symbol sizes is substantially continuous for practical purposes.
  • the largest apparent symbol size is about 1.5 log units.
  • the smallest apparent symbol size may be about -0.2 or -0.3 log units.
  • the preferred size increment/decrement between sequentially displayed symbols is 0.02 log units.
  • the symbol is usually displayed on or by a display means.
  • the display means may be capable of displaying a series of symbols sequentially in substantially the same area of the display means.
  • a suitable display means is a computer monitor, although other display means may be used, e.g. a television monitor or a projection screen with associated projection means.
  • Such display means typically present an image as a collection of illuminated or active pixel elements, each pixel element being individually operable. For such display means, the minimum change in displayed symbol size is therefore a single pixel element. Since the number of pixel elements is finite, the number of selectable symbol sizes is also finite .
  • the displayed symbol size is the absolute size of the symbol displayed, e.g. by the display means. As such, it can be expressed in terms of linear or area dimensions.
  • the apparent size of the displayed symbol is the size of the symbol as determined from the point of the view of the subject. This depends on the displayed symbol size and also on the distance between the subject's eye and the display means.
  • the apparent size of the displayed symbol can be expressed in terms of the angle which the displayed symbol subtends at the subject's eye, usually in log units. Usually, during a test, the distance between the subject's eye and the display means is fixed. Thus, a change in displayed symbol size brings about a corresponding change in apparent symbol size.
  • the present invention provides an apparatus for testing visual acuity of a subject, the apparatus including control means and display means, wherein the display means is controllable by the control means to display a series of symbols for attempted identification by the subject, the displayed size of each symbol being selected from a substantially continuous range of selectable symbol sizes.
  • control means is an electronic control means.
  • processing means such as a central processing unit.
  • the control means may also include memory means and/or data storage means.
  • control means is an electronic digital computer.
  • the display means is preferably a computer monitor operatively connected to the control means .
  • the computer may operate under the control of suitable software.
  • the data storage means may be used to store results of the test.
  • the apparatus may include data input means for inputting attempted identification information of each symbol to the control means.
  • the data input means may be a keyboard a mouse or similar. Alternatively, it may be a microphone combined with voice recognition means for converting speech from the microphone into electronic attempted identification data for each symbol. Attempted identification of each symbol may be input to the control means by the subject or by an assessor, i.e. person carrying out the visual acuity assessment e.g. optician, optometrist or other sight professional.
  • the data input means may be a keypad, e.g. for use by the subject, having letters or symbols corresponding to those displayed.
  • the present invention provides a computer-controlled visual acuity testing system including display means for displaying a series of symbols for attempted identification by a subject, wherein the displayed size of each symbol is selected from a substantially continuous range of selectable symbol sizes.
  • the system includes an apparatus according to the first aspect and/or preferred features mentioned with respect to the first aspect.
  • the present invention provides a method for testing visual acuity of a subject, wherein a series of symbols of varying displayed size is displayed to the subject for attempted identification by the subject, and wherein the displayed size of each symbol is selected from a substantially continuous range of selectable symbol sizes, the visual acuity of the subject being determined from the results of the series of identification attempts .
  • the following optional features are applicable to the general, first, second and/or third aspects of the invention, unless otherwise indicated.
  • the symbols are stored as sets of symbols.
  • suitable sets of symbols include Roman letter characters (upper and/or lower case) , Greek letter characters (upper and/or lower case) , other characters such as Arabic characters, Chinese characters, Japanese characters, numbers, symbolic drawings or ideographs .
  • a particular set of symbols is selected for a subject.
  • the set selected is upper case Roman letter characters.
  • symbols are preferably selected at random for display.
  • the same symbol is not displayed sequentially. Randomness of symbol selection ensures that a subject will not be able to use knowledge of prior tests to influence results of a test. This is an advantage over the known tests in which the limited number of variations of available charts led to subjects remembering letter sequences. This tended to reduce the value of the known tests-, since the subjects' memory of previous tests influenced the results of later tests.
  • the displayed size of sequentially displayed symbols may be selected in a predetermined way.
  • the apparent size of sequential symbols seen by the subject may be varied in a predetermined way.
  • the predetermined change in sequential displayed symbol size may be substantially logarithmic, i.e. the logarithm of the change in displayed size from one symbol to the next may be substantially equal.
  • the human sensory systems respond in a substantially linear fashion to logarithmic increments and decrements of stimulus and this is true of the visual system. It is for this reason that apparent symbol sizes are given in terms of log units.
  • the present- invention allows finer resolution of visual acuity threshold than previous testing systems.
  • the resolution using the invention is finer than 0.1 log units, preferably finer than 0.05 log units and more preferably about 0.02 log units .
  • the size increment/decrement between sequential displayed symbol sizes may be selected (e.g. by the control means or computer) on the basis of the results of the attempted identification of previously displayed symbols by the subject.
  • known predictive algorithms such as 'QUEST', 'PEST' and 'BESTPEST' may be used to step sequential symbol sizes based on previous identification attempts by the subject.
  • the preferred aim of the test is to provide a measurement (i.e. an estimation) of visual acuity of the subject. Preferably this is achieved by using a predetermined sequence or pattern of changes of displayed symbol size. For example, if the pattern is a randomly interleaved double staircase, this can give fast and accurate test results . The use of this pattern provides a more robust psychophysical measurement technique than the patterns used in known tests. The idea of the randomly interleaved double staircase was introduced by
  • Cornsweet (Cornsweet, T.N. (1962), "The staircase method in psychophysics . " Am J Psychol 75, 485-91) .
  • the stimulus parameter can be stepped up and down across the threshold (a single staircase) .
  • This has the disadvantage that the observer can predict the next presentation depending on the previous.
  • the randomly interleaved approach uses two staircases running concurrently and the stimulus presented at each presentation is chosen randomly from either staircase. The response to the stimulus controls the increment or decrement of that staircase for the next time it is presented. The advantage of this is the removal of predictability by the subject.
  • each symbol is displayed for a time ⁇ t' which may be varied at the start of the test, for example by suitable input to the control means by the assessor or by the subject.
  • a fixed time for each symbol seen by a particular subject improves the uniformity of subject performance.
  • Known tests do not easily allow for the display of symbols for a fixed period of time.
  • allowing the assessor to vary the time for symbol identification allows investigation of response of the visual system to time-dependent visual acuity.
  • the time ⁇ t' may be varied in different tests for the same subjects and/or for different subjects.
  • Time 't' may be varied during the test, usually by the assessor.
  • a variant of the test may be to display symbols of a fixed size for varying times 't' to measure the minimum time needed by a subject to resolve the symbols displayed.
  • the test might use a randomly interleaved double staircase with 't' as the variable .
  • each test symbol may be presented on the display means singly and/or in isolation.
  • This is a significant improvement over the known charts, which use lines of symbols, all the lines being presented to the subject at the same time, and the symbols of different lines having different sizes.
  • a further problem with the known charts thus stems from the fact that some letters on a particular line might be identified correctly by the subject and others might not. Such results provide difficulty in assessing visual acuity precisely.
  • providing only one test symbol at a particular apparent size avoids this problem.
  • One or more of the test symbols in a series of test symbols may be presented along with one or more dummy symbols. Preferably, in such a situation, there is still only one test symbol displayed at a time.
  • the use of dummy symbols can provide a useful crowding stimulus to the subject. This can give useful information on visual acuity. Dummy symbols may be displayed to the side and/or above/below the test symbol.
  • the test provides more than one measurement of visual acuity.
  • the measurements are subjected to statistical analysis. This can provide useful statistical parameters such as the mean measurement, the median and the standard error of measurement.
  • the standard error of measurement is the standard deviation of the measurements divided by the square root of the number of measurements for a population.
  • the test is stopped (e.g. by the control means) when one or more criteria are satisfied.
  • the test might be stopped when the measurement has been measured at least a predetermined minimum number of times, and: when the calculated standard error is below a predetermined value; or when the mean recognisability of the series of symbols displayed is within an acceptable value of the mean recognisability of the entire symbol set in use; or when the measurement has been measured a predetermined maximum number of times .
  • a typical predetermined value for the standard error criterion would be twice the resolution limit set for the test. Recognisability has been measured by others for
  • the test for a particular subject is tailored to that subject.
  • stored data on the visual acuity of the subject may be used to set up the test.
  • the displayed size of the first displayed symbol may be selected based on one or more previous visual acuity test results .
  • the previous test results may have been taken, e.g., one or more months or years before.
  • the data may be stored in the control means or in the data storage means .
  • a stored measurement of threshold of visual acuity of the subject may be used to. select the displayed size of the first symbol, which may be a predetermined ratio larger than the size corresponding to the stored threshold of visual acuity.
  • a symbol of large displayed size in comparison to the previously displayed size is displayed. This can be of assistance in keeping the subject's interest.
  • the identification of this large symbol by the subject is not included in an analysis of the attempted identifications of the test symbols by the subject, i.e. the large symbol is not usually treated as a test symbol in the test.
  • the processing means is operable to determine, for each input identification attempt by the subject, whether each identification attempt was successful or not.
  • these results are stored in an electronic database, e.g. in the data storage means or on an alternative data storage means such as a hard disk, floppy disk or optical disk.
  • the database has a structure allowing identification of the results in respect of the date of the test and the subject.
  • the database allows graphical representation of results.
  • the results may be presented graphically.
  • the measurement of visual acuity may be plotted as a function of time where several tests have been carried out over time. After each subsequent test, the graph can be updated.
  • Statistical analysis of the results allows an error estimation of each point on the graph, if desired.
  • lines of symbols can be displayed by the display means.
  • known tests can be simulated on the apparatus/system.
  • the display may show a layout similar to known logMAR or Snellen charts.
  • the acuity results obtained can be scored using one or more of the known scoring methods such as line score, single letter score, frequency of seeing curve and logistic regression.
  • the database is capable of providing comparisons between: the subject's visual acuity at different times, measured using the present method; the subject's visual acuity as measured using the present method and other methods (e.g. prior art methods and/or prior art methods carried out using the present system/apparatus) visual acuity of different subjects.
  • the system is also capable of generating and displaying means for other tests used for refraction and orthoptic assessment of subjects such as: duochrome test; fixation target; astigmatic fans; stereoacuity tests; and/or chromatic or achromatic contrast acuity
  • the present invention preferably provides a computer system including apparatus of first aspect.
  • the present invention preferably provides computer code or a computer code product (e.g. on a data carrier) suitable for carrying out the method of the third aspect when running on a computer.
  • the present invention preferably provides computer code or a computer code product (e.g. on a data carrier) suitable for converting a conventional computer to an apparatus according to the first aspect or a system according to the second aspect.
  • the present invention preferably provides a data carrier with a computer program stored on it, the computer program incorporating computer code according to the above aspects.
  • Fig. 1 shows a schematic illustration of a single staircase measurement technique.
  • Fig. 2 shows a schematic illustration of a randomly interleaved double staircase measurement technique .
  • the ordinate and abscissa have arbitrary units.
  • the ordinate axis may have units of log units, represent apparent symbol size, and the abscissa may merely indicate sequential symbols (letters) displayed during the test.
  • Fig. 1 the apparent symbol size is stepped up and down across the threshold, the increments and decrements in apparent symbol becoming smaller as the test progresses.
  • Fig. 2 there are two staircases running concurrently. The symbol displayed to the subject is chosen at random from either staircase. Both staircases are stepped up and down across the threshold.
  • a known computer is provided.
  • a computer program (software product) embodying the invention is loaded onto the computer.
  • the program may be stored on a CD-ROM, or it might be preloaded in the internal memory (ROM or RAM) of the computer.
  • ROM or RAM the internal memory
  • the exact nature of the computer code is not reproduced here, but it is to be understood that a suitable program may easily be obtained by suitable programming to follow the requirements set out below.
  • the visual acuity test will usually be carried out by an assessor such as an optician, optometrist or other sight professional on a subject whose visual acuity is to be tested.
  • an assessor such as an optician, optometrist or other sight professional on a subject whose visual acuity is to be tested.
  • the computer includes a CPU and RAM and a hard disk drive (ROM) .
  • the computer also includes peripheral devices such as a monitor and a keyboard and/or mouse. The computer monitor is kept in a fixed location during the test.
  • the software running on the computer causes the computer to display a preliminary user interface used for setting up the test.
  • Various information is input into the computer by the assessor (e.g. via the keyboard) using the preliminary user interface.
  • This information includes the identity of the subject, a unique identification code for the subject and the distance m between the subject's eye and the computer monitor screen.
  • the program uses m to calculate the apparent size of each displayed symbol in terms of the angle subtended by the symbol at the user's eye.
  • the assessor has the option of defining the minimum increment or decrement of displayed (or apparent) symbol size at the preliminary user interface. In turn this defines the resolution of the measurement of threshold of visual acuity which the test can achieve. Due to the use of a computer monitor, the size of the displayed symbol is determined by the number of pixels on the monitor spanned by the displayed symbol.
  • the assessor may select the initial symbol size to be displayed to the subject at the start of the test. This can help to reduce the total time taken to carry out the test by avoiding those apparent symbol sizes which are well removed from the previously measured threshold of visual acuity of the subject.
  • the test proceeds by a series of upper case Roman letters being displayed on the computer monitor.
  • the subject attempts to identify it by reading it out to the assessor.
  • the assessor either inputs the letter stated by the subject into the computer using the keyboard or inputs a result (i.e. "right” or “wrong”). Alternatively, the subject enters attempted identification data using a keypad. This allows self-assessment.
  • the computer stores the result in a temporary database (e.g. held on the RAM of the computer).
  • a temporary database e.g. held on the RAM of the computer.
  • the displayed size of the test letter may, for example, be stored as the number of monitor pixels spanned by the test letter, or the number of monitor pixels used to display the test letter.
  • Each test letter in the sequence is generated at random with the proviso that no two sequential test letters are the same letter.
  • Each test letter in the sequence has a different displayed size to the previous letter.
  • the pattern of displayed letter size changes may simply be logarithmic, i.e. the letters might change in displayed/apparent size logarithmically.
  • more reliable measurements of threshold of visual acuity are usually seen when the change in displayed letter size is in the form of a randomly interleaved double staircase.
  • Each test letter is presented singly for an identification attempt by the subject.
  • one or more of the test letters might be accompanied by dummy symbols (such as other letters) presented around the test letter. These may be of the same or different size to the test letter. These are present as crowding stimuli and may affect the ease with which the subject can identify the test letter. Therefore, if dummy symbols are presented with a test symbol, information about the dummy symbols is stored along with the result of the identification attempt by the subject.
  • a large-sized letter (in comparison to the size of the test letters) can be displayed, e.g. once every 3 to 5 letters. This is useful in maintaining the interest of the subject.
  • the test can stop, since a measurement has been obtained. However, it is preferred that further measurements are performed in order to gauge the reliability of the measurement.
  • the number of measurements made during each test is determined by certain criteria, e.g.:
  • the computer calculates the mean measurement and also the standard error of the measurements. These statistical parameters are stored by the computer.
  • the graphical representation of results can be made on the display.
  • the computer can also perform statistical comparisons (e.g. Student's t test) between interpretation of change in visual acuity over time.
  • the information stored by the computer as a result of the test is written to a permanent database, for example on the hard disk of the computer.
  • the information may be written to a portion of the permanent database associated with the particular subject. This allows time-dependent information about the visual acuity of the subject to be stored together in one location.
  • the information stored in the permanent database is capable of being displayed using a graphical interface, For example, known programs such as spreadsheets may be used to display the information collected during the test and compare it to previously collected information for the same or other subjects.
  • known visual acuity tests are reproduced or substantially reproduced on the computer monitor.
  • a Snellen Chart or a logMAR chart is reproduced on the computer monitor.
  • the results of the test are collected and stored in the same way as before, along with information about the test itself.
  • Known scoring techniques are then applied to the test results, such as line score, single letter score, frequency of seeing curve and logistic regression. These results can then be compared (e.g. graphically) with the results from the test of the previous embodiment.
  • the line score is determined by the smallest line of symbols (letters) which is read correctly.
  • each letter is ascribed a value of 0.02 log units. This amounts to a linear interpolation of letter size within the line sizes presented. It is often taken as the "gold standard" acuity measurement. See, for example, Ferris, F.I. Kassoff, A., Breswick, G. and Bailey, I., (1982), "New visual acuity charts for clinical research", Am J Opthamol 9_4, pp. 91-96.
  • a plot is made of the number of letters read correctly on each line, against the visual angle of each line. This is the appropriate way to score logMAR charts, which essentially presents five trials at each visual angle. Logistic regression can be used effectively to plot the frequency of seeing curve as a straight line, making interpolation easier.

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Abstract

L'invention concerne un appareil permettant de tester l'acuité visuelle d'un sujet. L'appareil comprend des moyens de commande (par exemple, un ordinateur numérique) et des moyens d'affichage (par exemple, un moniteur d'ordinateur). Les moyens d'affichage sont commandés pour afficher une série de symboles que le sujet essaiera d'identifier. Les dimensions affichées des symboles sont sélectionnées dans une gamme sensiblement continue, de manière à pouvoir obtenir des mesures précises de l'acuité visuelle par variation des dimensions affichées des symboles de faibles incrémentations proches du seuil de l'acuité visuelle du sujet.
PCT/GB2004/001581 2003-04-10 2004-04-08 Test de l'acuité visuelle Ceased WO2004089199A1 (fr)

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GB0308381.3 2003-04-10
GBGB0308381.3A GB0308381D0 (en) 2003-04-10 2003-04-10 Visual acuity testing

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007056796A1 (fr) * 2005-11-15 2007-05-24 Carl Zeiss Vision Australia Holdings Limited Systeme et procede de test visuel
US8888288B2 (en) 2011-02-23 2014-11-18 Nikoo Iravani Method and system for self-administering a visual examination using a mobile computing device
WO2014191986A1 (fr) * 2013-05-30 2014-12-04 Plotkin Boris Procédé de mesure d'acuité visuelle

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994013192A1 (fr) * 1992-12-14 1994-06-23 Institute Of Ophthalmology Test d'acuite visuelle
US5880814A (en) * 1996-10-30 1999-03-09 Mentor Corporation Visual acuity tester with improved test character generation
US5914772A (en) * 1997-08-29 1999-06-22 Eyelogic Inc. Method and device for testing eyes
WO2001021062A1 (fr) * 1999-09-24 2001-03-29 Fondazione Centro S. Raffaele Del Monte Tabor Appareil pour mesurer des performances visuelles

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994013192A1 (fr) * 1992-12-14 1994-06-23 Institute Of Ophthalmology Test d'acuite visuelle
US5880814A (en) * 1996-10-30 1999-03-09 Mentor Corporation Visual acuity tester with improved test character generation
US5914772A (en) * 1997-08-29 1999-06-22 Eyelogic Inc. Method and device for testing eyes
WO2001021062A1 (fr) * 1999-09-24 2001-03-29 Fondazione Centro S. Raffaele Del Monte Tabor Appareil pour mesurer des performances visuelles

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
BACH M: "THE FREIBURG VISUAL ACUITY TEST-AUTOMATIC MEASUREMENT OF VISUAL ACUITY", OPTOMETRY AND VISION SCIENCE, WILLIAMS AND WILKINS, BALTIMORE, MD, US, vol. 73, no. 1, 1996, XP002058541, ISSN: 1040-5488 *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007056796A1 (fr) * 2005-11-15 2007-05-24 Carl Zeiss Vision Australia Holdings Limited Systeme et procede de test visuel
US8152301B2 (en) 2005-11-15 2012-04-10 Carl Zeiss Vision Australia Holdings Limited Vision testing system and method
US8888288B2 (en) 2011-02-23 2014-11-18 Nikoo Iravani Method and system for self-administering a visual examination using a mobile computing device
WO2014191986A1 (fr) * 2013-05-30 2014-12-04 Plotkin Boris Procédé de mesure d'acuité visuelle
US10342421B2 (en) 2013-05-30 2019-07-09 Boris PLOTKIN Method for measuring visual acuity

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