Method for modifying the visual function of a subject, method for measuring the spherical correction need of a subject, and optical system for carrying out these methods

Abstract

To provide simple blurring and / or unblurring processes in which a target visual function is taken into account to determine a size of an optotype displayed in front of a subject, and to determine the value of spherical optical power of an optical component placed in front of the subject to alter his vision in order to blur or unblur it.SOLUTION: The invention relates to a method for altering a visual function of a subject using an optical system arranged in front of at least one eye of the subject, the method including: b) determining an optotype; c) displaying the optotype to the subject in such a way that it is visible by the subject through the optical system; d) assessing the visual function of the subject viewing the optotype through the optical system; and e) adding a positive or negative altering value of spherical optical power to the optical system.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a method for altering the visual function of a subject, in particular a method for assessing the visual acuity of the subject, and more particularly a method for identifying a level of optical correction for the subject's visual acuity during a test that may require blurring and / or unblurring the subject's visual acuity. [Background technology]

[0002] When assessing the refraction of each eye in a subjective test involving an attempt to read an eye chart and a visual target, it is important to control the accommodation of the eye to avoid incorrect assessment of the subject's subjective refraction and to ensure that the subject uses accommodation to focus on the target and answer the test correctly.

[0003] A common method of controlling accommodation is so-called blurring or fogging (these are synonyms), where in an initial blurring stage, blurring lenses are worn during the test to induce myopia. Then, in subsequent de-blurring stages, corrective lenses are used sequentially to de-blur the vision until best focus / best reading of the eye chart is obtained. As a result, a corrective sphere value is obtained, which is then used to shape the corrective lenses.

[0004] However, this is not an optimal method and is time-consuming, in particular because it does not take into account the initial visual performance level as a starting point for the blurring stage or the final visual performance to be reached at the end of the de-blurring stage, and does not take into account what may be obtained from the refraction provided by corrective lenses the subject may already have, or from the objective refractive error that may be or has been estimated or evaluated. It does not take into account other characteristics of the subject, such as age, other visual disorders, pupil diameter, etc. In addition, this method is not very well evaluated by the subject due to the imposed blurring.

[0005] Other methods of controlling accommodation are known, such as the use of cycloplegic eye drops to disable accommodation, but this can be dangerous, is not available to all professionals, and does not always produce reliable results, especially in children.

[0006] The use of a blurring lens in front of the eye being tested as discussed above in the fogging and then de-fogging method is a standard method with two possible end goals: best focus / best reading on the eye chart with maximum spherical power as discussed above, or a predetermined visual acuity (i.e., 0.1 log MAR, 0.0 log MAR, -0.1 log MAR).

[0007] Visual acuity may be scored based on the logarithm of minimum visual acuity: a subject who can distinguish details as small as 1 minute of visual angle has a visual acuity of 0 log MAR, since the common logarithm of 1 is 0; a subject who can distinguish details as small as 2 minutes of visual angle has a visual acuity of 0.3 log MAR, since the common logarithm of 2 is approximately 0.3; and so on.

[0008] In short, the formula used to determine visual acuity in log MAR is: VA(log MAR) = log(minimum visual acuity of subject's eye).

[0009] The advantage of quantifying visual acuity using log MAR units is that an increase in visual acuity tracks with a decrease in the size of the chart and therefore with an increase in the difficulty for the subject to distinguish the chart.

[0010] All of these blurring and / or deblurring methods have disadvantages with respect to the subject being examined, but are dependent on the operator using them for the quality of the results. [Prior art documents] [Non-patent literature]

[0011] [Non-Patent Document 1] Shah, N.; Dakin, SC; Whitaker, HL; Anderson, RS Effect of Scoring and Termination Rules on Test-Retest Variability of a Novel High-Pass Letter Acuity Chart.Investigative ophthalmology & visual science,2014,55,1386-1392 [Non-patent document 2] Hamm,LM;Anstice,NS;and … B.-J.Recognition Acuity in Children Measured Using The Auckland Optotypes.Ophthalmic and …2018 [Non-patent document 3] Hamm,LM;Yeoman,JP;vision,A.-N. of The Auckland Optotypes:An Open-Access Pictogram Set for Measuring Recognition Acuity.Journal of vision 2018 [Non-patent document 4] Lowery,JP;Hayes,JR;Sis,M.;Griffith,A.;Taylor,D.Pacific Acuity Test:Testability, Validity, and Interobserver Reliability.Optometry and Vision Science 2014,91,76-85 [Non-patent document 5] Frisen L. Vanishing Optotypes New Type of Acuity Test Letters.Arch Ophthalmol.1986 [Non-patent document 6] Blake, CR; Lai, WW; Edward, DP,<<Racial and Ethnic Differences in Ocular Anatomy.> > International Ophthalmology, 2003 [Non-Patent Document 7] W. Swaine,<<The relation of visual acuity and accommodation to ametropia> > Optician (1925) [Non-patent document 8] R. Blendowske,<<Unaided visual acuity and blur: a simple model> >Optom.Vis.Sci.92,e121-e125(2015) [Non-Patent Document 9] TWRaasch,<<Spherocylindrical refractive errors and visual acuity> >Optom.Vis.Sci.72,272-275(1995) [Non-Patent Document 10] J. Gomez-Pedrero et J. Alonso,<Phenomenological model of visual acuity> >,J Biomed Opt 21(12) 125005 (2016) Summary of the Invention [Means for solving the problem]

[0012] Here, a simple blurring and / or de-blurring process is proposed that takes into account the target visual function, determines the size of the vision chart to be displayed in front of the subject, determines the value of the spherical refractive power of the optical component to be placed in front of the subject, and changes his vision to blur or de-blur.

[0013] The method for altering a subject's visual performance according to the present invention may actually be implemented as a blurring method or a deblurring method, or may be implemented as part of a method that employs both a blurring and a deblurring step. In this last case, the method for altering a subject's visual performance may be used in each of the blurring and deblurring steps, or in only one of the blurring and deblurring steps.

[0014] When a method for changing a subject's visual function is used as a blurring process according to the present invention, the initial blurring step is carried out taking into account the visual characteristics of the subject in order to give the subject a predetermined visual function at the end of this blurring step.

[0015] During such a blurring stage, visual performance naturally decreases for the subject being blurred to relax his / her accommodation.

[0016] During any further deblurring stages, the number of attempts, or steps, to reach the target visual function for deblurring will be advantageously reduced compared to standard methods because the previous initial blurring stage has been optimized. Second, the repeated use of corrective lenses during the trials uses corrective lenses with non-uniform correction slope / difference levels, with the correction slope / difference gradually decreasing toward the end of the deblurring iteration, thereby achieving high accuracy for the method. This also allows the number of attempts to be reduced in the deblurring stage according to the present invention, preferably by only two or three attempts.

[0017] It is also advantageous that the subject perceives an improvement in his vision at each step of the deblurring phase. In the classical refraction process, the reduction in blurring occurs through identical steps that are not easily perceived by the subject. The method according to the invention therefore has a better chance of being well-accepted by the subject.

[0018] In the blurring (or fogging) step, a predetermined defocus goal to be achieved is selected for the subject, an eye chart is placed in front of the subject, and the subject's vision is defocused by placing lenses having a degree of defocus in front of the subject's eyes. The predetermined defocus goal corresponds to a target defocus level for the subject's eyes. This target defocus level corresponds to a target defocus level for the lenses to be placed in front of the eyes at the end of the blurring step.

[0019] This may be achieved in a single step, preferably through an iterative method whereby the subject's vision is gradually defocused by gradually changing the degree of defocus of lenses placed in front of the subject's eyes, the iteration method terminating when a predetermined defocus goal is achieved, during which the subject should provide responses regarding how he / she perceives the eye chart.

[0020] In practice, the desired defocus goal to be achieved is defined as the target visual function under conditions of cloudy / blurred vision.

[0021] This target visual function may be, for example, target visual acuity.

[0022] The eye chart may be standard letters, or any kind of image with high and low spatial frequencies, or a "vanishing" kind of image. Evaluation of the answers may be based on the method of limits, continuous or discrete methods, psychological methods, staircase methods, etc.

[0023] As opposed to a standard one-time initial blurring step, the initial blurring step according to the present invention may be an iterative method.

[0024] The termination of the iterative process may be objectively based on the value of the visual function, such as identifying visual acuity and comparing it to a target visual acuity, or subjectively based (eye chart, seen / recognized or not).

[0025] Preferably, in the case of the blurring step, the iterations are stopped when the eye chart is no longer visible.

[0026] The end of the iterative process may also be programmed to occur when a predetermined defocus goal is reached, i.e., when the ocular defocus level is achieved or the defocus target is achieved in the optical system.

[0027] Such an initial blurring or fogging step may be performed manually or may be automated.

[0028] Contrary to a standard initial blurring or atomization step, where the blurring step is the same for all subjects and environmental conditions, the initial blurring step according to the present invention may be adapted to each subject and environmental condition, as will be explained in more detail below.

[0029] The visual function of the subject is preferably determined at each step of the method.

[0030] For the de-blurring (or de-fogging) step, a predetermined visual performance goal to be reached is selected for the subject and an eye chart is placed in front of the subject.

[0031] The subject's vision is then focused (actually refocused) in one step or, preferably, in an iterative process, which may be done incrementally and repeatedly, the iterative process terminating when a predetermined focusing goal is reached or when maximum visual acuity is reached.

[0032] During this iterative process, the subject must provide answers about how he / she perceives and reads the eye chart, which may take the form of several question-and-answer games.

[0033] This allows the subject's visual acuity to be determined at each step of the method.

[0034] In practice, the predetermined focusing goal to be achieved is defined as the target visual function expected when the subject is in a corrected state.

[0035] The predetermined focusing goal to be achieved may be best focus / best reading of an eye chart, or a predetermined visual acuity (ie, 0.2 log MAR, 0.1 log MAR, or 0.0 log MAR).

[0036] The eye chart may be standard letters, numbers, symbols, or any type of significant image (i.e., one that has meaning to the subject) with high and low spatial frequencies, or a "disappearing" type of image.

[0037] Evaluation of responses may be based on marginal methods, continuous or discrete methods, psychological methods, staircase methods, etc.

[0038] The termination of the iterative process is based objectively on the value of visual function, such as identification of visual acuity and comparison with target visual acuity, or subjectively (eye chart that is either clearly seen / recognized or not). The de-blurring (or de-fogging) step may be performed manually or may be automated.

[0039] More precisely, the invention relates to a method for modifying the visual performance of a subject using an optical system placed in front of at least one eye of the subject, comprising the following successive steps: b) identifying an eye chart; c) displaying the eye chart identified in step b) to the subject in such a way that the eye chart is visible by the subject through the optical system; d) evaluating the visual function of the subject by viewing the eye chart displayed in step c) through an optical system; and e) adding a change value of the spherical power to the optical system, said change value being positive or negative.

[0040] According to the invention, the method further comprises, before step b), a) selecting a visual function target value; In steps b) and e), the size of the vision chart and the change value of the spherical refractive power are specified as a function of the target value of the visual performance.

[0041] In other words, in steps b) and c), the vision chart has a size specified according to the target value of the visual function, In step e), the change value of the spherical power is determined depending on the target value of the visual performance.

[0042] Advantageously, the method further comprises: - step f) of assessing the subject's visual function after step e) and defining the result of this assessment as a current value of the visual function; - repeating steps c), d), e), and f) until the current value of the visual function reaches the target value of the visual function or an extreme value of the visual function, or remains stable or deviates from the target value; The change in the spherical power to be added to the optical system in each step e) is determined as a function of the target value of the visual function and of the current value of the visual function determined in the previous step d).

[0043] In a preferred embodiment, the method for altering visual function is a method for blurring the subject's vision.

[0044] Therefore, in this blurring method, the goal of the change is to blur the subject's vision to relax his / her accommodation, and the change value of the spherical refractive power is positive to bring the subject into a myopic state with blurred vision and relaxed accommodation.

[0045] Preferably, if the subject is used to wearing ophthalmic correction devices, said subject is wearing his / her ophthalmic correction devices or his / her objective refraction as a starting point for recognizing the vision chart during step d).

[0046] Advantageously, the blurring method comprises, in step d), asking the subject whether the eye chart is recognizable, visible or invisible through the optical system, and in step e), adding a positive change value of spherical power, the positive change value being determined as a function of the subject's answer, the previously added change value and the target value of the visual function.

[0047] Preferably, in step e), the positive change value is determined by the subject: - he / she sees and recognizes the eye chart, or - he / she looks at the eye chart and does not recognize it, or - Whether he / she sees the eye chart or not, It depends on whether you answer yes or no.

[0048] Other advantageous and non-limiting features of the blurring method according to the present invention include: - The eye chart is a disappearing eye chart; in step a), the disappearing eye chart is chosen at random, for example, from among the following disappearing letters: D, H, K, N, R, S, V, and Z; The disappearance type vision chart has a magnitude that is larger than the target value of visual function by a predetermined value, for example, 0.1 log MAR.

[0049] The visual minimum is the smaller visual angle that the eye can detect. An eye chart placed at a given distance from the subject's eyes, for example 6 meters, corresponds in size to the visual acuity.

[0050] In practice, the visual acuity of a subject corresponds to the smallest visual acuity chart size discernible by the subject at a given fixed distance and is expressed as log MAR.

[0051] When assessing visual acuity using a visual acuity chart, the visual acuity corresponds to the width of the lines that limit the chart. The height of the visual acuity chart is generally higher than that of a classical visual acuity chart for the same visual acuity. The correspondence between the size of the visual acuity chart and visual acuity is established for a visual acuity chart in the form of letters. A correction coefficient depending on the visual acuity value must be taken into account.

[0052] For non-letter-deleted eye charts, other corrective factors may be taken into account to infer visual acuity. These corrective factors may depend on the visual acuity itself.

[0053] Some of these corrections are described in Non-Patent Document 1, Non-Patent Document 2 and Non-Patent Document 3.

[0054] In certain embodiments, the eye chart can be randomized and / or changed after recognition, if desired.

[0055] In another embodiment, the method also includes: f) assessing the subject's visual function after step e) and defining the assessment result as a current value of the visual function; Steps c), d), e), and f) are repeated until the current value of the visual function reaches, remains stable, or deviates from the target value of the visual function; the change in spherical power to be added to the optical system in step e) is determined as a function of the target value of the visual function and of the current value of the visual function, This involves repeating steps c), d), e), and f) while the size of the eye chart remains the same.

[0056] In certain embodiments of this blurring method, the defocus level and the visual performance are correlated via a mathematical formula.

[0057] This formula may take into account different models linking the visual function of the subject's eye to the level of defocus, which may be constructed on data collected while performing the blurring / blurring steps on the subject and / or by computer learning algorithms.

[0058] For example, environmental deviations such as light reflections on the display screen or poor lighting conditions may be detected and taken into account through these computer learning algorithms.

[0059] In a particular embodiment of the method, the visual acuity target value identified in step a) and subsequently selected is: - the purpose of the blurring or de-blurring step in the subject's eye examination; - the subject's personal characteristics, -adapted according to one of the environmental parameters.

[0060] In certain embodiments of the method, the visual acuity target value is determined in step a) by taking into account a model linking the defocus level of the eye with the visual function of the eye, which model is constructed on data collected while performing the blurring / deblurring steps on the subject and / or by a computer learning algorithm.

[0061] In another preferred embodiment, the method for altering visual performance is a method for deblurring vision in a subject, comprising: the effect of the change is to deblur the subject's vision to reach the target value of said visual function for one or both eyes of the subject, the optical system initially has an additive change in spherical power such that the subject is initially in a myopic state with blurred vision and relaxed accommodation, - evaluation of the visual function of the subject looking at an optotype through the optical system in step d) makes it possible to deduce the subject's level of defocus; and The change value of the spherical power added in step e) is negative in order to de-blur the subject's vision and is determined from the target value of visual performance and from said defocus level.

[0062] In a particular embodiment of this de-blurring method, the defocus level and the visual performance are correlated via a mathematical formula.

[0063] Alternatively, the defocus level is compiled from the visual performance.

[0064] The defocus of an optical system placed in front of a subject is the spherical power of the lens placed in front of the subject's eye.

[0065] The defocus level is defined as the defocus state of the subject's eye. This defocus level depends on both the refractive error of the eye and the defocus degree of the optical system. The zero defocus level of the eye corresponds to the state of the eye with emmetropia, where no lens is placed in front of the eye. This can be achieved, for example, by placing a negative spherical lens in front of a myopic eye or a positive lens in front of a hyperopic eye.

[0066] According to a further embodiment of the method, f) assessing the subject's visual function after step e) and defining the assessment result as a current value of the visual function; Steps c), d), e), and f) are repeated until the current value of the visual function reaches, remains stable, or deviates from the target value of the visual function; The change value of the spherical refractive power to be added to the optical system in step e) is determined according to the target value of the visual performance and the current value of the visual performance; Step b) is repeated, and in each step b) the size of the visual chart is determined according to the target value of the visual function and the current value of the visual function.

[0067] In one embodiment of the present invention, in step b), - the uncertainty of visual performance for the current defocus level of the optical system is identified; Two rows of the eye chart are identified, and the number of letters or symbols per row, the number of rows, and the size difference between two adjacent rows are identified based on the uncertainty of visual acuity.

[0068] In one embodiment of the present invention, the visual acuity target value identified in step a) is: - the purpose of the blurring or de-blurring step in the subject's eye examination; - the subject's personal characteristics, -adapted according to one of the environmental parameters.

[0069] In one embodiment of the present invention, the visual acuity target value is determined in step a) by taking into account a model linking the defocus level of the eye with the visual function of the eye, which model is constructed on data collected while performing the blurring / de-blurring steps on the subject and / or by a computer learning algorithm.

[0070] The present invention also provides a method for determining the spherical refractive correction need of a subject, comprising: - carrying out a method for blurring the subject's vision; - implementing a method for deblurring the vision of said subject according to the invention, said initial myopic state resulting from implementation of said method for deblurring, - the successively added negative change values ​​of the spherical power of successive iterations of step e) are added together to define the de-blur spherical power, the need for spherical refractive correction is determined based on said deblurring spherical power.

[0071] More precisely, the successively added negative change values ​​of the spherical refractive power of successive iterations of step e) are added together to define a deblurred spherical refractive power until the current value of the visual function reaches the target value of the visual function or before the current value of the visual function remains stable or deviates from the target value, and the need for spherical refractive correction is identified based on the deblurred spherical refractive power.

[0072] In a preferred embodiment of the method for determining the need for spherical refractive correction, the method for blurring is one of the methods described above according to the invention.

[0073] In certain embodiments of the method for measuring spherical refractive correction, f) assessing the subject's visual function after step e) and defining the assessment result as a current value of the visual function; Steps c), d), e), and f) are repeated until the current value of the visual function reaches, remains stable, or deviates from the target value of the visual function; The change value of the spherical refractive power to be added to the optical system in step e) is determined according to the target value of the visual performance and the current value of the visual performance; Step b) is repeated, and in each step b) the size of the visual chart is determined according to the target value of the visual function and the current value of the visual function.

[0074] The present invention comprises a system configured for carrying out the blurring method intended to induce relaxation of accommodation in the eye according to the present invention, said system comprising an optical device that is placed in front of at least one eye of a subject and configured to impart additional spherical refractive power to said eye, wherein said spherical refractive power is variable.

[0075] Similarly, the present invention provides an optical system for carrying out the method according to the present invention, which may be configured in particular for carrying out the blur removal method according to the present invention, said system comprising an optical device that is placed in front of at least one eye of a subject and is configured to impart additional spherical refractive power to said eye, wherein said spherical refractive power is variable.

[0076] The present invention provides 1) a blurring method according to the present invention, and / or 2) A system configured for continuous execution of the deblurring method according to the present invention.

[0077] The present invention aims to optimize and personalize the blurring and / or deblurring process. In particular, the deblurring method according to the present invention allows deblurring while searching for the maximum convex sphere that provides a specific visual function or the best visual acuity. The estimation of the defocus level performed by measuring the subject's blurred visual acuity allows for faster and more accurate deblurring.

[0078] The method of the invention optimizes the optical examination in order to match the blurring and / or de-blurring lenses to the subject's visual perception and function in a more accurate manner.

[0079] It also aids in patient acceptance of optical testing as it is simpler, more progressive and less frustrating for the patient.

[0080] It is also possible to reduce the influence of the operator in performing the test, thereby minimizing the variability of the subjective refraction measurements. The method can be implemented in a dedicated system and run automatically.

[0081] Finally, the new method was developed to reduce the time required to perform the test, in order to prevent the subject from becoming fatigued by too significant an effort of concentration, which could lead to errors in the measurement of subjective refraction.

[0082] Contrary to known methods, an automated method may be implemented and used at any step of the vision test where de-blurring is recommended as a function of, i.e. depending on, the subject's focusing state.

[0083] The following description, enriched by the accompanying drawings, which should be considered as non-limiting examples, will help to understand the invention and to find out how it can be put into practice. [Brief explanation of the drawings]

[0084] [Figure 1] FIG. 1 shows the change in the spherical power of the optical device in diopters as a function of time during the iterations / steps of the method for blurring. [Figure 2] Figure 2 shows three vanishing vision charts. [Figure 3] FIG. 3 shows a display for entering trial results for blurring. [Figure 4] FIG. 4 shows the change in the spherical power of the optical device in diopters as a function of time during the iterations / steps of the method for deshading. [Figure 5] Figure 5 shows a visual acuity board that displays an eye chart type visual acuity chart, and the corresponding visual acuity is shown in log MAR. [Figure 6] FIG. 6 is a display for entering the results of trials for deblurring, showing the corresponding visual acuity in log MAR. [Figure 7] FIG. 7 shows a model of the curve with vertical defocus δ and horizontal visual acuity AV (log MAR) that is used to calculate the change in refractive power at each iteration / step of the method. [Figure 8] FIG. 8 shows examples of defocus levels of a subject's eyes as a function of the corresponding visual acuity of the identified eye for subjects in different age categories. [Figure 9] FIG. 9 shows examples of defocus levels for subjects' eyes as a function of the corresponding visual acuity of the identified eye for subjects with different visual impairments. [Figure 10]FIG. 10 shows an example of the uncertainty range of visual acuity for a given level of defocus for a subject's eye. [Figure 11] FIG. 11 shows an example of the uncertainty range of the eye's defocus level for a given visual acuity of a subject. DETAILED DESCRIPTION OF THE INVENTION

[0085] In the following description, the defocus value corresponds to the value in diopters of the spherical power of the lens placed in front of the subject's eye during the blurring or de-blurring stage of the method.

[0086] This defocus value is an added value compared to the initial value of the spherical power placed in front of the eye before the blurring or de-blurring step.

[0087] To facilitate understanding of the embodiments further described, the invention will now be described in more general terms.

[0088] According to the present invention, a method for modifying the visual performance of a subject using an optical system placed in front of at least one eye of the subject comprises the following steps in succession: b) identifying an eye chart; c) displaying an eye chart to the subject in such a way that the eye chart is visible by the subject through the optical system; d) assessing the subject's visual function by viewing an eye chart through the optical system; e) adding a change in spherical power to the optical system, said change in power being positive or negative; The method further comprises, before step b), a) selecting a target value of visual function; and in step c), the visual acuity chart has a size specified according to the target value of the visual function; In step e), the change value of the spherical refractive power is determined according to a target value of the visual function.

[0089] Generally, steps c), d) and e) may be repeated in several iterations.

[0090] The method for modifying the visual performance of a subject may in particular be used in either the blurring or de-blurring stage of a visual acuity test. The present invention also relates to a method comprising a blurring and de-blurring stage, at least one of which stages is carried out according to the present invention.

[0091] Visual function may refer to objective or subjective characteristics of a subject's vision. In particular, visual function may be assessed by determining the subject's visual acuity or by determining the level of perception for a particular eye chart.

[0092] The level of perception may be one of three: the eye chart is clearly visible, the eye chart is blurred, or the eye chart is not visible. At the first level, the eye chart is recognized without difficulty, at the second level, it is recognized with difficulty, and at the third level, it is not recognized. The time required by the subject to identify the eye chart may identify which level of perception the subject has reached.

[0093] The level of perception may alternatively be one of two: the eye chart is recognized or not.

[0094] With respect to visual acuity, any known method for determining visual acuity may be used.

[0095] The optical system placed in front of the subject may comprise a set of different lenses with different powers that can be placed alternatively or cumulatively in front of the subject's eyes to provide different spherical powers, or may comprise lenses with adjustable spherical power, such as liquid lenses. In either case, the spherical power of the optical system may be varied. The variation may be applied manually or via a computer-controlled motorized device.

[0096] The general blurring process of the present invention is as follows: 1) Asking the subject to look / stare / fixate on a visual stimulus and describe his perception of the visual stimulus; 2) modifying the level of focusing as a function of the subject's response describing the visual stimulus, i.e., according to an individual estimate; 3) Having a stopping criterion that defines when a good / target level of defocus or defocus degree of the optical system has been reached.

[0097] In practice, the visual stimulus is an eye chart displayed in step b). As will be explained in more detail below, the perceptual description of the visual stimulus allows the visual function of the subject viewing the eye chart through the optical system to be assessed in step d).

[0098] In step a), a target value of the visual performance is identified, which corresponds to a defocus target, i.e. in this case to blurred vision.

[0099] The blurring step according to the present invention may be adapted to each subject and environmental conditions, as will be explained in more detail.

[0100] In the blurring step, the visual performance target or the predetermined defocus goal may be adapted in practice, for example depending on the purpose of this blurring step in the eye examination of the subject.

[0101] It may actually be different if the blurring step is performed before the unsharpening step, to identify the mask values ​​before assessing the balance between the eyes or to achieve a binocular refraction test according to the Humphris method, such a mask may be used, for example, to suppress the central vision of one eye while preserving the peripheral vision.

[0102] Before the blurring step, the aim is to suppress monocular accommodation by selecting a low visual acuity target, ie, the visual performance target may be an acuity of 0.4 log MAR.

[0103] Before assessing binocular balance, the aim is to ensure that the images seen by the left and right eyes are comparable, i.e. the visual target may be 6 / 10 or 8 / 10 visual acuity.

[0104] If a blurring step is performed to identify the value of a mask to be placed in front of the eyes to perform a binocular refraction test according to the Humphris method, the visual performance target may be a visual acuity of 5 / 10.

[0105] In the blurring stage, the visual acuity target in the blurred state may also depend on the subject's personal characteristics such as the subject's age, refractive error, the subject's geographic origin, eye diseases (cataracts), previous prescriptions, the subject's ocular history such as pupil diameter, etc.

[0106] The younger the subject, the more their eyes tend to accommodate. Visual acuity targets should therefore be lower for younger subjects to ensure accommodative relaxation.

[0107] For example, visual acuity goals may be equal to 2 / 10 for children under 12 years old, 4 / 10 for teenagers between 12 and 18 years old, and 6.3 / 10 for adults due to the low risk of accommodation.

[0108] The visual acuity target for blurring may also take into account eye diseases such as cataracts and their effect on ocular clarity, i.e., the visual acuity target may be 4 / 10 for elderly subjects with cataracts or 6 / 10 for elderly subjects without cataracts.

[0109] Visual performance target values ​​for blurring may also be specified depending on environmental parameters, such as parameters of the measurement setup.

[0110] Lighting conditions can affect the contrast of an eye chart, and therefore its perception changes with lighting. In low lighting conditions, the visual performance target is set to a lower value than in bright lighting conditions. Bright lighting conditions reduce the apparent contrast of targets on the screen.

[0111] As a further example, it may depend on the distance between the subject's eye and an optical system comprising a blurring / de-blurring lens and / or a corrective lens placed in front of the subject's eye.

[0112] This distance may actually affect the optical magnification through the optical system and therefore the visual acuity that is specified.

[0113] A convex lens magnifies an object viewed through it, whereas a concave lens reduces the size of the same object viewed through a concave lens. In other words, the image of an object viewed through a convex lens is larger than it actually is, whereas the image of an object viewed through a concave lens is smaller.

[0114] The effect (magnification or reduction) depends on the power and / or width of the lens and the distance between the lens and the subject's eye. For example, a subject with a high degree of myopia and a -8 diopter corrective lens placed 20 mm from the subject's eye will have a visual acuity goal for blurring of about 5 / 10 when the lens is placed 10 mm from the eye, whereas for a subject with hyperopia, the visual acuity goal for blurring can be set at 8 / 10 for a lens placed 20 or 10 mm, with the corrective lens placed in front of the eye magnifying the image of an object.

[0115] Without considering these criteria, a mean visual acuity target of 4 / 10 for blurring may be used to moderate the subject's accommodation.

[0116] In step b), the eye chart is identified, in particular the eye chart size associated with the corresponding visual acuity.

[0117] For the blurring stage, the size of the eye chart is set in the first iteration of steps c), d), and e). It is specified according to the visual performance goal. When other iterations of the steps are performed, the size of the eye chart remains the same.

[0118] Therefore, in the case of the blurring stage, step c) is repeated with the same eye chart.

[0119] In step d), the visual performance of the subject viewing an eye chart through the optical system is assessed, for example, in step d) of the blurring stage, the subject's current visual performance relative to the current eye chart is determined.

[0120] This may be done, for example, via a visual acuity test as described below, or by subjective perceptual testing to identify a level of perception, such as a test assessing whether a letter is recognized or not recognized, or whether it is seen or not seen. Any known visual or visual acuity test may be administered.

[0121] In step e) a change in spherical power to the optical system is added, said change being positive.

[0122] The spherical power of the optical system placed in front of the subject is therefore modified by adding an increment of positive defocus in front of the subject's eye, which can be done either by adding a lens with a spherical power equal to the increment or by changing the spherical power of a liquid lens.

[0123] The increment of spherical power to be added is determined according to the visual performance goal, and preferably also takes into account the current visual performance determined in step d).

[0124] Finally, this increment of spherical power is applied to the optical system in a defocus step.

[0125] The specification of the defocus target, and therefore the spherical power increment of the optical system, may be achieved by taking into account any one of several models for specifying the visual threshold, for example, by Lowery and Shah, 1999. These models are presented in the publications "Lowery and Shah, 1999," and "Lowery and Shah, 1999," both of which are incorporated herein by reference.

[0126] Other models may also be used, some of which may be established, for example, by statistical processing of data collected while performing the blurring / de-blurring steps.

[0127] These models predict visual function, e.g., visual acuity observed in different categories of subjects as a function of the defocus of the lenses placed in front of the subjects' eyes. Examples of these data are shown in Figures 8 and 9.

[0128] In either case, the determined defocus degree can be applied to the optical system in one step or in several steps. The advantage of applying the defocus degree in different steps is that the initial determination of the defocus level of the eye when the vision is blurred is less accurate than the determination of the defocus level of the eye in subsequent steps when the vision is not so blurred. The subsequent steps allow for improved accuracy to reach a predetermined goal of visual performance without exceeding this goal.

[0129] According to the present invention, the model may also be constructed by computer learning algorithms, through which deviations from the environment, such as light reflections on the display screen or poor lighting conditions, may be detected and taken into account.

[0130] Due to the established relationship between visual acuity and defocus, the current defocus level of the eye corresponding to the current defocus of the optical system may be deduced from the current visual acuity value via a curve such as those in Figures 7, 8, and 9, or via a table. Similarly, the defocus target may be deduced from the visual acuity target. The difference between the defocus target and the current defocus provides the required increment of defocus.

[0131] The stopping criteria may be objective (eg, visual acuity) or subjective (seen / not seen).

[0132] In fact, in the embodiment described here, for the blurring step, defocusing is performed iteratively until a target level of blurring is reached, said target level being generally defined by a target visual function.

[0133] The variation of the spherical power of the optical device placed in front of the eye of the subject to be examined is carried out by iterations / steps. One step or several steps may be considered.

[0134] For example, according to the two points shown in Figure 1, the second point - the latter - corresponds to a defocus that has reached the target level for blurring. It is important to understand the term "reaches" as meaning that the current defocus is close to, equal to, or exceeds the target defocus, as the case may be.

[0135] In practice, the achieved blurring level is estimated based on the subject's visual function, for example, based on the subject's visual acuity at which the subject's vision is blurred. The target blurring level is considered to be reached if the achieved blurring level is within an uncertainty range from the target blurring level. The uncertainty range for the degree of defocus placed in front of the subject's eyes depends on the visual acuity target, as shown in Figures 10 and 11. This is due to the magnifying effect of the lens and the subject's perceptual difficulties when the vision is blurred.

[0136] For example, for a 2 / 10 visual acuity target, the uncertainty range is approximately 0.5 diopters, whereas for an 8 / 10 visual acuity target, the uncertainty range is approximately 0.2 diopters.

[0137] It is also important to understand that the curve in Figure 7 from which the points are taken was obtained during studies on a population of subjects, and that the curve is preferably a curve adjusted based on the results of those studies, and more preferably is based on a mathematical curve calculated from a formula developed from the results of those studies.

[0138] Having such a formula can be useful in implementing an automated system, where the points are calculated from the formula. In a simplified implementation, a table of points can be preset and retrieved when the blurring or de-blurring process is performed. More about curves is explained below.

[0139] Instead of formulas, tables may be used.

[0140] Yet, in reality, the subject is in front of a screen that displays an eye chart by means of an optical device, which screen is viewed in close proximity to his / her subject's eye.

[0141] For example, during the repetition of the display, the subject must indicate the eye chart that he / she cannot recognize or the last one that he / she can recognize. In Figure 2, three examples of eye charts corresponding to the decrease in the level of visual acuity reached, i.e., corresponding to the lower level of visual acuity reached, are shown from left to right.

[0142] As an example of an implementation of the blurring process in a process-adaptive system, 1) The subject stares at the disappeared target. 2) The expert will inform the subject of the guidelines. 3) The expert incrementally increases the blurred sphere by clicking on the subject's answers if the implementation is not fully automated.

[0143] The question to ask the subject might be: "Can you read the letters on the board / wall? I'm going to put lenses in front of your eyes. Let me know if you no longer recognize the letters or if they are too blurry / indistinct to see."

[0144] Instructions to the professional may be: "To control accommodation, reduce the subject's vision to fixation acuity, then ask how the letters are perceived and verify the subject's answer as indicated by clicking the corresponding button on the system." Possible answers include: - Characters are visible and recognized, - Characters are visible but not recognized, -The characters cannot be recognized.

[0145] The instructions to the professional may continue as follows: “Continue to the end of the test to get an accurate measurement of the cloud value. Click the button to cancel the last response given. Click the button to return to the beginning of the test."

[0146] The professional may use a computer system displaying images such as those in Figure 3 to input the test results during the process. It is also possible to adapt the system to the needs. For example, the initial screen of the system allows the user to select a target visual acuity of 0.2 log MAR, 0.4 log MAR, 0.7 log MAR, or 1.0 log MAR. It is also possible to change the type of characters to avoid memorization artifacts.

[0147] Here, preferably, the displayed image is located at a fixed distance of 6 m from the subject, so the visual perception of a given displayed eye chart depends only on its size on the screen.

[0148] Moreover, the size of the eye chart may be adjusted according to its distance to the eye to accurately identify visual acuity.

[0149] The eye chart is preferably a disappearing type of visual target that allows for a quick assessment of defocus and has a method that is easily understood by the subject.

[0150] "Vanishing optotype" targets were first described by Howland et al. in 1978. These optotypes have a pseudo-high-pass design so that the mean luminance of the target is the same as the background; therefore, the stimulus disappears shortly after reaching the resolution threshold.

[0151] The center of the eye chart is black (100% contrast) with a white surround (0% contrast), and the test background is gray (50% contrast), with the surround being half the thickness of the black center.

[0152] Contrast is defined here as the difference in luminance between the considered area and its surroundings divided by the luminance of said surroundings.

[0153] 100% contrast indicates that the area is as black as possible. A contrast of 0% indicates that the area is as white as possible. A contrast of 50% indicates that the area is a medium gray.

[0154] In a vanished chart, the average luminance of the chart, including its outline, is equal to the luminance of the chart's background.

[0155] For visual perception or functional assessments or visual acuity assessments, it is preferable to present the subject with letter sizes slightly different from those corresponding to the target visual acuity at 100% contrast. Boards or display letters are used, each consisting of a single letter of different sizes: "N" at 0.3 log MAR, "Z" at 0.5 log MAR, and "V" at 0.7 log MAR, for example, as shown in Figure 2.

[0156] In other implementations, the targets may be different, especially with different spatial frequencies or different types of symbols (Landolt C, Sloan numerals, eye charts for children). Other vanishing eye charts are known, for example the Oakland Eye Chart for Children, or see [5].

[0157] Depending on the target visual function, the increment of the refractive power of the blurring lens at each iteration, or more generally the iteration in diopters δ, must be adapted.

[0158] This increment or repetition amount is defined so that the subject perceives the difference between each lens passing in front of the eye, and also accommodates the variability in visual performance measurements made at different blurring levels.

[0159] The precise level of blurring is theoretically determined by passing as few as three lenses in front of the wearer's eyes, for each size of character. The number of iterations is preferably between 0 and 3, which corresponds to a process with only one to four steps.

[0160] The number of steps depends on the initial conditions of the blurring method: if the subject is already blurred initially (e.g., a subject with uncorrected myopia), fewer than three steps are required, whereas if a lens with excessively negative power is placed in front of the eye, more steps may be required to defocus the subject's eye.

[0161] Below is a table summarizing the proposed target and blurring lens characteristics according to the desired (target) visual function.

[0162] [Table 1]

[0163] Since in most cases the patient sees well through the optical system at the beginning of the test, large increments of spherical power are generally used for the first step of changing the power. Subsequent iterations may use smaller or larger increments depending on the current visual function identified with the current spherical power. The final iteration preferably uses small increments.

[0164] FIG. 1 shows one example of incremental adjustment as a function of time.

[0165] For example, an objective refraction measurement may be performed before performing the blurring step to provide an initial value of the refraction of the subject's eye. If this objective refraction value is close to the subjective refraction value, the first eye chart presented to the subject will correspond to this objective refraction value and will therefore be correctly identified by the subject.

[0166] The defocused lenses are then placed in front of the subject's eyes in high increments, for example 0.45 diopters for a visual acuity goal of 0.4 log MAR, optionally repeated.

[0167] The subject then identifies the eye chart but indicates that it is slightly blurred. The defocus of the lens (lens assembly or adjustable liquid lens) is increased in smaller increments, for example, 0.15 diopters.

[0168] The blurring stage ends when the subject indicates that they can no longer see the eye chart.

[0169] If the subject has myopia and does not wear corrective lenses, his vision is already blurred at the start of the blurring stage. Fewer steps are required to achieve the blurring stage.

[0170] Regarding the deblurring process, the following are possible: 1) Asking subjects to look / gaze / fixate on visual stimuli in an "interactive manner"; 2) correcting the focusing level in n steps, where n is a value lower than the standard method by individual estimation as a function of the subject's visual function, and preferably n is comprised between 1 and 3 steps; 3) Having a stopping criterion that defines when a satisfactory / target level of focusing or visual performance has been achieved.

[0171] By interactive method, it is meant that the subject is asked to read or describe the eye chart that he or she sees.

[0172] In practice, the visual stimulus is an eye chart displayed in step b). As will be explained in more detail below, the perceptual description of the visual stimulus allows the visual function of the subject viewing the eye chart through the optical system to be assessed in step d).

[0173] It is assumed here that the subject's vision is initially blurred due to any blurring steps performed prior to it due to vision defects in the eye without compensation.

[0174] In step a), a target value of the visual function is determined, which here corresponds to a focusing target. As will be explained below, the visual function target may be determined according to different criteria, including criteria linked to the subject himself, which allows for individualization of the method. The visual function here is the function that must be achieved to ensure optimal vision for the subject, if necessary with corrective lenses.

[0175] In the deblurring stage, steps c) to e) are generally repeated for several iterations. Additionally, step b) is also repeated.

[0176] In the first step b), the size of the eye chart displayed in step c) is determined solely based on the visual performance target, or alternatively, it may be a fixed size eye chart or determined from the target visual acuity value of a previous blur test.

[0177] In each step d), the current value of the visual function is determined. This is done, for example, by a visual acuity test based on the subject's description of his perception of the currently displayed visual acuity chart. Any known visual acuity test may be used.

[0178] In step e), a negative increment of the spherical power of the optical system placed in front of the subject is determined by taking into account the visual function target determined in step a) and, preferably, the current value of the visual function determined in step d).

[0179] In the next iteration, in step b), a modified visual acuity chart may be determined based on the visual function target, preferably also taking into account at least the current value of the visual function determined in the previous step d).

[0180] In the deblurring step, the eye chart preferably comprises two rows of a fixed number of letters of a predetermined size corresponding to visual acuity.

[0181] Each line may have, for example, 1 to 10 characters.

[0182] The characters in each line have a predetermined size. The sizes of the characters in each of the two lines are usually different.

[0183] Therefore, in step e), the size of the visual acuity chart determined may correspond to the size of the characters in only one line. In step e), the number of characters or symbols per line, the number of lines, and the size difference between two adjacent lines may also be determined based on the visual function target. They may also take into account at least the current value of the visual function determined in the previous step d).

[0184] In particular, in step b), The uncertainty of visual performance for the current defocus level of the optical system is determined. Two rows of the eye chart are identified, and the number of letters or symbols per row, the number of rows, and the size difference between two adjacent rows are identified based on the uncertainty of visual acuity.

[0185] In this way, the number of characters or symbols per line, the number of lines, and the size difference between two adjacent lines may also be specified based on the uncertainty of visual acuity for the current degree of defocus of the optical system.

[0186] If the uncertainty is higher than a predetermined threshold, the size difference between the two lines may be increased or the number of characters may be decreased.

[0187] If the uncertainty is below another predetermined threshold, the size difference between the two lines may be decreased, or the number of characters may be increased.

[0188] For example, for the initial step of determining visual acuity, the subject's vision is assumed to be blurred, making it more complicated to perform the visual acuity measurement than if the subject's vision were not so blurred.

[0189] For an eye defocus level of 1.5 diopters, the uncertainty range of visual acuity is 0.2 log MAR, so the difference in magnitude between two adjacent rows may be 0.2 log MAR, i.e., for example, 0.5 log MAR and 0.7 log MAR for the first and second rows, respectively.

[0190] For a 0.5 diopter defocus, the uncertainty range of visual acuity is 0.1 log MAR, so the difference in magnitude between two adjacent lines may be 0.1 log MAR. Furthermore, because we have a more accurate measurement, we can display more characters on each line.

[0191] For the de-blurring (or de-fogging) step, a predetermined focusing goal to be reached is selected for the subject's test and an eye chart is placed in front of the subject.

[0192] This predetermined focusing goal corresponds to, or is specified based on, a target visual acuity.

[0193] An embodiment of the deblurring process will now be described in more detail.

[0194] The deblurring of the present invention is a simple process that allows for the search of the sphere by measuring the visual function when the visual system is in a defocus state, so that an expert measures the visual function, i.e., specifies the visual acuity, and the deblurring is automatically performed according to the defocus state estimated based on the specified visual acuity.

[0195] Generally, in step a), a predetermined focusing goal value, also called visual acuity target or focusing target in the following, is fixed at a visual acuity value equal to 10 / 10. The final set of visual acuity charts displayed at the end of the deblurring method is then required to test the vision for this visual acuity.

[0196] The visual acuity target may be adapted, for example, depending on the purpose of this de-blurring step in the subject's eye examination.

[0197] It may certainly be different if the de-blurring step is performed before another test is performed to confirm the spherical refraction of the eye, before confirming the astigmatism of the eye, e.g., the cylinder and / or axis of the eye, or before performing a final test before prescribing a refractive correction.

[0198] Before a separate test is performed to determine the spherical refraction of the eye, the visual performance target may be, for example, a visual acuity of 8 / 10, with some blurring still present.

[0199] Before determining the degree of astigmatism of the eye, the visual performance target may be, for example, a visual acuity corresponding to no blur without accommodation of 10 / 10.

[0200] Before the final examination before prescribing refractive correction, the visual performance target may be set to a maximum value corresponding to the average best visual acuity, for example 12 / 10.

[0201] The visual performance target value may also be adapted according to the subject's personal characteristics, such as the subject's estimated maximum visual acuity, which may be estimated according to the subject's ocular history, such as age, refractive error, the subject's geographic origin, eye diseases (cataracts), previous prescriptions, etc.

[0202] It is known that visual acuity does decline as a subject ages due to a decrease in the clarity of the eye and a decrease in the efficiency of processing signals from the retina.

[0203] Visual acuity goals may be set, for example, at 8 / 10 for those over 60 years of age and 12 / 10 for young adults.

[0204] It is also known that ocular anatomy varies slightly depending on the geographic origin of the subject, as is known from Non-Patent Document 6. The visual acuity target for Asian subjects can be set at 8 / 10, as this is the average maximum observed for subjects of these origins. The visual acuity target is set at 10 / 10 for Caucasian subjects.

[0205] The subject's visual acuity is also determined by the pupil diameter, i.e., the maximum achievable visual acuity increases with increasing pupil diameter up to a pupil diameter of 3 mm, then gradually decreases for pupil diameters above 3 mm due to optical aberrations, and stabilizes at an intermediate value. Therefore, visual acuity targets can be specified according to the pupil diameter in the lighting conditions of the process.

[0206] Refractive error also has an effect, as discussed in the following paragraphs, since corrective lenses used in front of the eye during the method according to the invention tend to increase or decrease the size of the vision chart. The vision target may therefore be smaller for a myopic subject, since corrective lenses decrease the size of the vision chart, and larger for a hyperopic subject, since corrective lenses tend to increase the size of the vision chart.

[0207] Visual performance targets may also be specified depending on environmental parameters, such as parameters of the measurement setup: lighting conditions can affect, for example, the contrast of an eye chart, the perception of which therefore changes with lighting.

[0208] For example, it may depend on the distance between the subject's eye and an optical system comprising a blurring / de-blurring lens and / or a corrective lens placed in front of the subject's eye.

[0209] This distance may actually affect the optical magnification through the optical system and therefore the visual acuity that is specified.

[0210] A convex lens magnifies an object viewed through it, whereas a concave lens reduces the size of the same object viewed through a concave lens. In other words, the image of an object viewed through a convex lens is larger than it actually is, whereas the image of an object viewed through a concave lens is smaller.

[0211] The effect (magnification or reduction) depends on the power and / or width of the lens and the distance between the lens and the subject's eye. For example, a subject with a high degree of myopia and a -8 diopter corrective lens placed 20 mm from the subject's eye will have a visual acuity target of approximately 8 / 10 or 10 / 10 when the lens is placed 10 mm from the eye, whereas for a subject with hyperopia, the visual acuity target can be set at 12 / 10, with the corrective lens placed in front of the eye magnifying the image of an object.

[0212] If the subject was previously blurred to a visual acuity of 0.4 log MAR, it is preferred to perform the deblurring step in three iterations. This deblurring method may nevertheless be adapted depending on the initial blurring level reached after the blurring step, the target visual function, etc. A deblurring step performed in 1 to 5 steps is preferred.

[0213] The primary objective is for the subject to achieve a predetermined visual function using only three blur relief lenses, or within a predetermined number of blur relief lenses, rather than a variable number of blur relief lenses as in the standard method.

[0214] for that, 1) The subject gazes at an eye chart such as that shown in Figure 5. 2) Visual acuity is assessed by line verification if 4 out of 5 letters in this line are read / understood correctly, where the line corresponds to the assessed visual acuity. 3) Automatically, a deblurring lens is placed in front of the subject's eyes and a vision board corresponding to the target function is presented. 4) A new vision board will appear. 5) If the target visual function is not achieved, the specialist will reassess the visual function until the expected result is achieved.

[0215] Preferably, as previously mentioned, during deblurring, two rows of a predetermined number of eye charts are displayed, each row corresponding to a different visual acuity.

[0216] During this repetitive process, the following instruction may be directed to the subject: "What is the smallest line of letters you can decipher even obscurely without squinting or closing your eyes behind a hiding place?"

[0217] If two lines of an eye chart are displayed, the instruction might be: "Can you read the bottom line? If not, can you read the top line?"

[0218] If the target value of visual function cannot be reached, i.e., if the current value of visual function is stable or deviates from the target value (the extreme value of visual function that has been reached), the repetition of steps c) to f) is stopped.

[0219] In this case, the successively added negative spherical powers identified in step e) for all iterations before stabilization or deviation from the target value are added together to define the de-blur spherical power that provides the best visual acuity.

[0220] This deblur sphere power is the required spherical correction, in other words the value of the spherical correction that gives the subject the best visual acuity.

[0221] On his / her side, the professional may have to follow the following instructions: "Approach the sphere accurately. Ask them to read the lines of text. Continue until the progress bar is complete. The test ends when the patient achieves at least 10 / 10 visual acuity. Manually correct the sphere if necessary. Verify the subject's response as indicated by clicking the corresponding button. The possible answers are -All lines are read, -Part of the line is read, -Not a single line is read. The sphere and sharpness plate are then corrected so that the patient has a visual acuity of better than 10 / 10. The sphere can also be changed manually by means of the corresponding buttons. Continue this way until you have finished the inspection to get closer to the sphere. To cancel your last answer, press the corresponding button. To return to the start of the test, press the corresponding button. To open the shutter that displays the test progress in detail, press the corresponding button. To cancel the last answer given, press the corresponding button. To return to the start of the test, press the button. To open a section with detailed information about the progress of the scan, click the corresponding button.

[0222] The professional may use a computer system displaying images such as that of Figure 6 to input results during the process, which may also be used by the subject to input results directly into the computer system.

[0223] It is also possible to customize the system, in particular to select the visual function goals that the patient can achieve, and to randomly change the visual acuity chart to avoid the effects of memorization.

[0224] We now describe how the amount of change in optical power of the optical device is determined at each iteration through the blurring and de-blurring process.

[0225] The scientific literature presents numerous articles describing laws correlating the visual performance achieved by different types and levels of defocus. Based on these laws, the method of the invention calculates a proposed deblurring lens according to the measured visual performance and the target visual performance that it is expected to reach in several steps.

[0226] Several authors have described models for estimating the level of defocus in the visual system as a function of measured visual acuity, most notably Swaine, Raasch, Blendowske, and Gomez.

[0227] The focusing step, and therefore the determination of the increment of spherical power of the optical system, may be achieved by taking into account any one of several models for determining the threshold of vision, which are described in the publications [7], [8], [9] and

[10] .

[0228] These models are based on different criteria and are not universal.

[0229] According to the present invention, the amount of change in the refractive power of the optical device at each iteration of the blurring and de-blurring process may take into account different parameters such as visual characteristics, i.e., astigmatism, axis, pupil diameter, personal characteristics such as age or gender, or environmental factors such as lighting conditions.

[0230] According to the invention, it is proposed to use the model shown in Figure 7 with vertical defocus δ and horizontal visual acuity AV (log MAR). This model in Figure 7 follows Swaine's law for very low defocus levels (0δ~0.5δ), Gomez's law for small defocus levels (0.5δ~1.75δ), and Blendoske's law for strong defocus levels (>1.75δ).

[0231] This model in FIG. 7 is approximated by the following equation: Spherical defocus of the eye = -2.2236 (VA) 3 +4.7411(VA)2 +0.263(VA)+0.2039 where VA = visual acuity (log MAR).

[0232] This formula is used in an automated system to calculate the amount of optical power to add or subtract to the optical device at each iteration of the process.

[0233] Again, the primary objective is for the subject to reach a predetermined visual acuity by passing through a fixed number of de-blurring lenses, rather than a variable number as in the standard method.

[0234] For this purpose, the proposed method includes determining the visual acuity of the subject and estimating the spherical defocus state of the subject's eye following the blurring step using the above formula and the determined visual acuity. Calculation of the power of the deblurring lens to be used is performed to achieve intermediate visual acuity, which allows a better estimation of the defocus state value.

[0235] As an example, we use the actual deblurring lens reduction value (70%) calculated to be recommended to achieve the target visual function without obtaining a value that is too concave. The sphere value was calculated and then rounded to the nearest hundredth of a diopter. This choice also depends on the variability of the measurement of the visual function of deblurring. The sphere value was calculated and then rounded to the nearest tenth of a diopter.

[0236] The number of steps depends on the initial conditions and the visual performance goal: if the subject is really blurred to begin with (e.g., a subject with high myopia without correction), three steps are needed, whereas if he starts with no blur or only slight blur (a myopic subject with correction), fewer steps will be needed as the visual acuity goal is achieved.

[0237] Depending on the visual function with blurring and the visual function the specialist wishes to achieve, it is recommended to perform the test in a certain number of repetitions / steps (= number of deblurring lenses), i.e. from 1 to 5 repetitions, preferably 2 or 3 repetitions.

[0238] Examples of blurring include: Start blurring at 1.0 log MAR and with 3 iterations / steps, 1) De-smear 70% of the values ​​to reach 0.4 log MAR, 2) De-blur 70% of the values ​​to reach 0.0 log MAR, 3) Deblur the 100% value to reach 0.0 log MAR (if not reached before). Start blurring at 0.7 log MAR and with 3 iterations / step, 1) De-smear 70% of the values ​​to reach 0.3 log MAR, 2) De-blur 70% of the values ​​to reach 0.0 log MAR, 3) Deblur the 100% value to reach 0.0 log MAR (if not reached before). Blurring starts at 0.4 log MAR and with 2 iterations / step, 1) De-blur 70% of the values ​​to reach 0.0 log MAR, 2) Deblur the 100% value to reach 0.0 log MAR (if not reached before). If the starting visual acuity is 0.2 log MAR, only one deblurring lens is used. 1) De-blur 70% of the values ​​to reach 0.0 log MAR, As another example, for deblurring, 1) If the subject's blurred visual acuity is 0.7 log MAR, then blur removal is performed at 0.91 δ. 2) If the subject's blurred visual acuity is now 0.5 log MAR, then de-blur is performed at 0.73 δ. 3) If the subject's blurred visual acuity is 0.1 log MAR, then unblur 0.18 δ.

[0239] Visual acuity was 0.0 log MAR and only three lenses were taken to achieve a visual acuity of 0.0 log MAR.

[0240] In certain cases, if the visual acuity target is not reached in the deblurring method, it is suggested that the spherical power change value added in the last step e) be positive to ensure that the subject has his maximum visual function at the maximum spherical power.

[0241] For example, if the same visual acuity is measured for three different powers of one or more lenses placed in front of the subject, the method is stopped and the first value of the power having the same visual acuity is considered to identify the subject's need for spherical refractive correction.

[0242] According to another embodiment, if the subject's answers indicate twice a visual acuity that is lower than the previously measured visual acuity, the method is stopped and the first value of the power with the best visual acuity is considered.

[0243] According to another embodiment of the method according to the invention, a final visual acuity target of, for example, 10 / 10 should be achieved.

[0244] In the first embodiment, - If the measured visual acuity is less than 2 / 10, the intermediate visual acuity target is set to 4 / 10, which corresponds to the first step towards the final visual acuity target. The corresponding defocus level is determined and applied according to the formula Eq. 10 mentioned above. A visual acuity chart of the size corresponding to 4 / 10 visual acuity is displayed. - If the measured visual acuity is greater than 2 / 10 and less than 4 / 10, the intermediate visual acuity target is set to 5 / 10, which corresponds to the first step towards the final visual acuity target. The corresponding defocus level is determined and applied according to the formula Eq. 10 mentioned above. A visual acuity chart of the size corresponding to 5 / 10 visual acuity is displayed. - If the measured visual acuity is greater than 4 / 10 and less than 8 / 10, the visual acuity target is the final visual acuity target. The corresponding defocus level is determined and applied according to the formula Eq. 1. A visual acuity chart of the size corresponding to the final visual acuity is displayed. If the measured visual acuity is greater than 8 / 10, the visual acuity target is the final visual acuity target. The defocus level is set to 0.2 diopters and applied. An eye chart of the size corresponding to the final visual acuity is displayed.

[0245] When using an eye chart displayed in two rows of different sizes, the eye chart of the size corresponding to the visual acuity sought is placed on the bottom row.

[0246] In the second embodiment, - If the measured visual acuity is greater than 2 / 10 and less than 4 / 10, the visual acuity target is the final visual acuity target. The corresponding defocus level is determined by the formula Eq. above, and 70% of this defocus level is applied. A visual acuity chart of the size corresponding to the final visual acuity is displayed. - If the measured visual acuity is greater than 4 / 10 and less than 8 / 10, the visual acuity target is the final visual acuity target. The corresponding defocus level is determined and applied according to the formula Eq. 1. A visual acuity chart of the size corresponding to the final visual acuity is displayed. If the measured visual acuity is greater than 8 / 10, the visual acuity target is the final visual acuity target. The defocus level is set to 0.2 diopters and applied. An eye chart of the size corresponding to the final visual acuity is displayed.

[0247] The maximum total defocus value is, for example, 1.6 diopters.

[0248] In the embodiment described herein, the visual performance target is a visual acuity target, but other targets may be considered, such as low contrast visual acuity, dynamic visual acuity, children's visual acuity, reading speed, contrast sensitivity, etc.

[0249] The spherical power of the corrective lens required by the subject to achieve the visual performance goal is determined based on the spherical power of the optical system at the end of the de-blurring phase, i.e., when achieving the visual performance goal.

Claims

1. 1. An optical system for modifying a visual function of a subject to blur and / or de-sharpen the subject's vision to achieve a visual function target value, the visual function target value corresponding to a defocus target for an eye of the subject, the optical system comprising an optical device arranged to be placed in front of at least one eye of the subject and to impart additional spherical refractive power to said eye, the optical system being arranged to perform a method comprising the successive steps of: a) determining a target value of visual function taking into account the visual characteristics of the subject; b) specifying an acuity chart having a size determined according to the target value of the visual function; c) displaying the eye chart identified in step b) to the subject in such a way that the eye chart is visible by the subject through the optical system; e) adding a change in spherical power to the optical system, the change being positive or negative and determined according to the target value of the visual function; 1. An optical system comprising:

2. 2. The optical system of claim 1, wherein the goal of the change is to blur the subject's vision and the change value of the spherical power is positive to bring the subject into a myopic state with blurred vision and relaxed accommodation.

3. The method comprises: - asking the subject whether the eye chart is visible or not through the optical system; - in step e) adding a positive change value of the spherical refractive power, said change value being determined as a function of the subject's answer, the previously added change value and the target value of the visual function, 3. The optical system of claim 2.

4. In step e), the change value is determined by the subject: - he / she sees and recognises the eye chart, or - he / she does not recognise the eye chart when he / she sees it, The optical system according to claim 3 , wherein the optical system is configured to respond to the request.

5. The optical system of claim 4 , wherein the eye chart is a vanishing eye chart.

6. 6. The optical system of claim 5, wherein in step a), the disappearing eye chart is randomly selected from among the following disappearing letters: D, H, K, N, R, S, V, and Z.

7. The visual acuity target value identified in step a) is as follows: the purpose of the blurring or de-blurring step in the eye examination of said subject, - the personal characteristics of said subjects, The optical system according to any one of the preceding claims, adapted depending on one of the following: - environmental parameters.

8. The optical system according to any one of claims 1 to 7, wherein the additional spherical power is adjustable.

Images