Myopia monitoring application

Abstract

1. A method for monitoring the progress of a visual acuity value of a user (1) of a digital device (2), the digital device (2) being configured to display optotypes in a selected optotype size for the user (1) to guess and to calculate a guessing rate corresponding to a proportion of optotypes correctly identified by the user (1), the method comprising the steps of: a) determining a visual acuity reference value (VA_ref) based on at least a predefined first guessing rate threshold (THS) of optotypes displayed in an optotype reference size (OS_ref); and b) testing the progress of the visual acuity value, the step of: b1) displaying an optotype in a first optotype size corresponding to the optotype reference size (OS_ref) and measuring the guessing rate of the displayed optotype, and if the measured guessing rate falls below the first guessing rate threshold (THS) by more than a tolerance value (ε), b2.1) testing the progress of the visual acuity value by re-measuring the guessing rate of an optotype displayed in a second optotype size (OS2.1) that is higher than the first optotype size.

Description

[Technical field]

[0001] The present invention relates to the field of vision assessment, and more particularly to myopia monitoring using mobile applications. [Background technology]

[0002] To assess an individual's visual acuity, an appointment with an ophthalmologist is often required. To detect possible refractive shifts and thus changes in the individual's visual acuity, complex equipment is usually used and specific measurements are performed by the ophthalmologist. Furthermore, there is no easy way for an individual to evaluate his or her visual acuity and its development between two different appointments, often several months apart. In particular, the development of an individual's visual acuity allows identifying potential refractive errors (e.g., myopia, hyperopia, astigmatism) and / or monitoring the development of such refractive errors. In the case of myopia, the progression of which may be particularly pronounced in children, visual acuity monitoring may allow to check the visual acuity of an individual periodically and to detect a worsening or stabilization of myopia. In practice, the worsening of an individual's myopia is reflected in a decrease in the visual acuity of that individual. Visual acuity monitoring also makes it possible to evaluate the efficiency of such eye treatment, for example in the case of certain eye treatments aimed at preventing eye deterioration and / or slowing the development of refractive errors.

[0003] Existing solutions for determining an individual's visual acuity fail to provide a simple, efficient and accurate method that an individual can perform themselves on a regular basis. Summary of the Invention [Problem to be solved by the invention]

[0004] Thus, a problem exists regarding being able to accessibly and simply, yet accurately, monitor the progression of an individual's own visual acuity in order to monitor the progression of underlying refractive errors such as myopia. [Means for solving the problem]

[0005] The present invention addresses such problems.

[0006] In a first aspect of the invention, a method for monitoring the evolution of a visual acuity value of a user of a digital device is proposed, the digital device comprising: - displaying the optotype at the selected optotype size to allow the user to guess; - measuring a guessing rate corresponding to the proportion of correctly identified symbols by the user, The method is: a) determining a visual acuity reference value, the visual acuity reference value being determined based on at least a predefined guess rate threshold of a visual target displayed at a visual target reference size; b) testing the progress of visual acuity values, - displaying the optotype at a first optotype size corresponding to the optotype reference size; - Measure the guess rate of the displayed stimulus, - if the measured guess rate falls below the guess rate threshold by more than the tolerance; b2.1) Re-measure the guess rate for the stimulus displayed in a second stimulus size that is superior to the first stimulus size and testing the progress of visual acuity value by Includes.

[0007] As a result, an individual can measure the progress of his / her vision without the need for any complicated equipment or an appointment with an ophthalmologist. Using a basic digital device, an individual can perform a vision test and repeat such vision test daily, weekly, or monthly to evaluate the progress of vision over time. In particular, the myopia monitoring method provides a modified repetition of the vision test based on challenging the last updated level of the individual's vision. Thus, with each new vision test, it is possible to detect a potential deterioration of the individual's vision between two consecutive vision tests. Such a method is particularly suitable for myopic users, such as myopic children, since myopia in children often progresses quickly and requires frequent monitoring. Thus, myopia monitoring can be easily performed periodically, for example, at home using personal or shared digital data, such as a mobile phone, tablet, or computer. Furthermore, the use of a psychometric function linking the guess rate of the optotype and the visual acuity provides an accessible and easily understandable method to be performed by a user, for example, a child. Thus, such a method can be performed, for example, daily or weekly. In addition, the tested level of visual acuity, and therefore any changes in the size of the displayed visual acuities, are calculated and updated over time by the digital device, so that the user does not need to set any initialization data or provide any specific medical input, such as, for example, a visual acuity progress record.

[0008] Furthermore, the method allows obtaining data related to the progress of an individual's visual acuity. By measuring such progress via measurements, remeasured guess rates corresponding to specific target sizes (and thus specific visual acuity values), the result data provided by the proposed method is easily interpretable, for example, for the individual (e.g., a child) and / or for others (e.g., by implication, the individual's relatives, such as parents, etc.).

[0009] Visual acuity is understood as a measure of the spatial resolution that the human eye is capable of perceiving. That is, if two points are separated by a sufficient distance for a given human eye, such human eye is capable of distinguishing two distinct points. However, if such distance is too small, the human eye is unable to distinguish between two distinct points. The quantification of such sufficient distance corresponds to visual acuity. More generally, the visual acuity of the human eye can be defined based on the minimum size or angular size of a visual target that an individual can reliably discern. Such a minimum angular size is called the "minimum angular resolution" (or MAR) and is expressed in arc minutes (or arcmin).

[0010] The visual acuity value or level may then be defined as a decimal value or fraction corresponding to the reciprocal of the minimum visual angle. For example, if an individual's MAR is 1 arcmin, then the individual's visual acuity is 1.0, or 10 / 10. If an individual's MAR is 4 arcmin, then the individual's visual acuity is 1 / 4, or 2.5 / 10.

[0011] Optotypes or eye charts can be understood as graphical symbols, figures or letters displayed to an individual with a predefined optotype size. Optotypes can be, for example, letters in a Landolt C or Snellen eye chart. Optotype size, also called optotype detail size, can be understood as the angular size (expressed in arcmin units) at which an individual perceives the displayed optotype. Such angular size is defined in particular taking into account the individual's distance from the symbol to be read. Optotype size can also be understood as the absolute size of the optotype on the display surface, expressed in millimeters. The angular size of the optotype can be estimated via a tangent formula based on the absolute size of the optotype and the individual's distance from the optotype to be read.

[0012] As a result, given a constant physical distance between the individual's position and the surface on which the target is displayed, the target size of the displayed target corresponds to the minimum visual angle (or MAR) that can be uniquely tested and is therefore related to the visual acuity level that can be uniquely tested.

[0013] Displaying visual symbols is understood as the digital device displaying a series of several visual symbols on the screen of the digital device. The digital device can be held by a user and positioned by the user so that the screen of the digital device faces a reflective surface such as a plane mirror. The user can therefore see the visual symbols displayed on the mirror as a virtual image. The screen can also be positioned to face the user so that the displayed visual symbols are directly seen by the user on the screen. The visual symbols are displayed to the user as a series of visual symbols of the same size, and visual symbols of the same series are displayed consecutively. The series of visual symbols may be displayed by the digital device in the same line.

[0014] The guess rate is understood as the ratio or proportion of the number of symbols correctly guessed or identified by the user to the total number of symbols in the series of symbols displayed to the user. One guess rate is defined for a series of symbols displayed with a given symbol size. That is, one guess rate can be associated with one visual acuity level to be tested. The highest guess rate is that 100% of the symbols are correctly identified by the user. The lowest guess rate is the probability of blindly guessing the correct symbol. For example, if the displayed Landolt C has eight random orientations, the probability of randomly guessing the correct orientation of the displayed Landolt C is 1 / 8 or 12.5%.

[0015] A guess rate threshold is understood as a predefined certain guess rate value that defines a satisfactory rate of good responses. That is, when a series of optotypes are displayed with a given optotype size, when the user reaches a guess rate equal to or close to the guess rate threshold, the visual acuity level corresponding to the given optotype size is considered to be the correct level of the user's visual acuity at the time of testing. Alternatively, if the guess rate is much higher than the guess rate threshold (e.g., beyond a predefined tolerance value), the tested optotype size may be larger than the user's minimum visual angle (in other words, the user may be able to identify smaller optotypes while still meeting accuracy). If the guess rate is much below the guess rate threshold, the optotype size is considered to be below the user's minimum visual angle, leading to the user being unable to accurately guess the displayed optotype. In one embodiment, the guess rate threshold is between 50 percent and 70 percent.

[0016] By tolerance is understood the allowed percentage error of the guess rate for which the guess rate is considered to correspond approximately to the guess rate threshold. In one embodiment, the tolerance is between 5 percent and 15 percent. For example, if the guess rate threshold is 60 percent and the tolerance is 10 percent, all guess rates that are between 50 percent and 70 percent of correct guesses are considered to correspond to the guess rate threshold. Such a tolerance makes it possible to compensate for imprecision of the method, in particular linked to the probabilistic aspects of the guess rate measurement. The value of the tolerance can be predefined in particular depending on the number of symbols displayed with a given symbol size. For example, the tolerance can be predefined to 10 percent for guessing 10 symbols displayed with a given symbol size and 5 percent for guessing 20 symbols displayed with a given symbol size.

[0017] The optotype reference size is understood as the optotype size at which the user reaches a first guess rate threshold when guessing the optotype displayed at such optotype size. The optotype reference size thus corresponds to the minimum visual angle of the user. The visual acuity reference value is understood as the visual acuity level determined to be the correct visual acuity level of the user at the time of the test. Such visual acuity reference value may be defined as the inverse of the optotype reference size. The visual acuity reference value defines the visual acuity of the user at a certain time. The visual acuity of the user may change over time with respect to such visual acuity reference value or, conversely, may be stabilized to such visual acuity reference value.

[0018] By measuring the guess rate, it is understood that the digital device can collect and process the user's responses in response to a series of displayed symbols at a given symbol size to identify a guess rate associated with the tested symbol size (i.e., the tested visual acuity level). For example, the user can vocally express his / her response at each displayed symbol, and such vocal responses can be received, for example, by a microphone of the digital device. The user can also make gestures to indicate his / her response, and such gestures can be received by a front camera of the digital device. The displayed symbols can also include a movable cursor that the user can control using a physical switch of the digital device (such as the plus and minus buttons of a mobile device). In such a case, the user's response is received by the camera, which detects the position of the movable cursor with a predetermined latency.

[0019] A user is understood as an individual who uses a digital device to monitor his / her vision progress. The user can perform the monitoring method with or without eye correction (such as corrective glasses or lenses) on one eye (monocular vision testing situation) or on both eyes (binocular vision testing situation).

[0020] A visual acuity test is understood in particular to be a method performed at a given time, which consists in displaying to a user, by a digital device, a sequence of symbols of certain symbol sizes, and in determining by the digital device a guess rate corresponding to such symbol sizes based on receiving a response from the user in response to the display of the symbols.

[0021] Re-measurement of guessing rates of optotypes displayed with a second optotype size that is a superordinate of the first optotype size is understood to mean that a new series of optotypes having a new optotype size (here, the second optotype size) is displayed to the user such that a new guessing rate (here, the re-measured guessing rate) is determined based on the response provided by the user in response to such new series of optotypes. The second optotype size is not determined randomly. Such a second optotype size is a superordinate of the first optotype size, meaning that a lower level of visual acuity is tested on the user compared to the immediately preceding visual acuity test performed on the user. Such a method relies on the assumption that a decrease in the ability to correctly identify optotypes reflects a decrease in the visual acuity level of the myopic user.

[0022] The new series of symbols at the second symbol size can be displayed to the user after a predetermined time period from the previously displayed series of symbols. Such a time period can be one or several days. By separating the separate vision tests in time, an accurate progression of vision can be obtained. When monitoring the eye to observe the effect of a particular eye treatment, separate vision tests spaced in time can obtain the medium to long term effect of the treatment on the individual's vision.

[0023] In a second aspect of the invention, a digital device is proposed comprising a communication interface with at least one screen, a man / machine interface and a processing circuit configured to implement the method according to the first aspect of the invention.

[0024] Such a digital device allows the user to perform the self-monitoring method in a simple and accessible manner. Indeed, such a digital device can be handled by the user. Such a digital device can correspond, for example, to the user's tablet or smartphone. Advantageously, the proposed method can be performed using a digital device that is used daily by the user and that the user can easily access.

[0025] In a third aspect of the present invention, a server is proposed, connected to a communication network and having a storage memory storing a database for implementing a method according to an embodiment of the first aspect of the present invention, said database being accessible by at least one terminal and providing at least a history of the evolution of the visual acuity value to a user of said terminal.

[0026] Such a server may be a remote server, such as a cloud platform. The server may receive data and signaling from any digital device connected to the communication network. As a result, the server may advantageously centralize the information and data collected and measured by the digital devices. The server may also be used as an intermediary to provide the data provided by the proposed method to other individuals, remote from the user of the digital device, who are interested in and / or have the ability to interpret the data collected by the digital device.

[0027] In a fourth aspect of the invention, a computer program product is proposed comprising program instruction code stored on a computer readable medium for carrying out the method according to the first aspect of the invention.

[0028] According to one aspect of the invention, a method comprises the steps of: If the measured guess value exceeds the guess rate threshold by more than the tolerance, b2.2) further comprising re-measuring the guess rate for the displayed object at a third object size that is smaller than the first object size.

[0029] As a result, the method allows to provide modified monitoring, particularly when it is detected that the user's hyperopia has progressed over time. In such a case, a third target size is tested in the next visual acuity test performed on the user. Such a third target size corresponds to a higher visual acuity level compared to the visual acuity level tested in the immediately preceding visual acuity test.

[0030] According to one aspect of the invention, a method comprises the steps of: If the gap between the measured guess rate and the guess rate threshold is less than or equal to the tolerance, b2.3) further comprising re-measuring the guess rate for the displayed target with a target size equal to the first target size.

[0031] As a result, the method allows testing the stability of the user's myopia by repeating a vision test at the same vision test level, such a new vision test being performed after a predefined time period since the previous vision test, such predefined time period being, for example, several days.

[0032] In fact, if the guessing rate measured at the first target size at a given time leads to a guessing rate that approximately corresponds to the guessing rate threshold, the visual acuity test level (corresponding to the first target size) is deemed to be the correct visual acuity level of the user at the given time. In other words, it is deemed that the guessing rate of the user when the target size is displayed at the first target size at the current time is not significantly different from the guessing rate of the user when the target is displayed to the user at the target reference value. In that case, the next visual acuity test is performed later to check whether such visual acuity reference value remains valid.

[0033] In one embodiment, the guess rate is re-measured after a predefined period of time, which in one embodiment is a number of days or more.

[0034] Advantageously, the monitoring method is carried out by spacing different visual acuity tests in time so as to be able to observe the exact progression of the user's visual acuity.

[0035] In one embodiment, the method comprises: c) determining a progression of the user's visual acuity value by comparing the visual acuity reference value with at least one other visual acuity value determined by the digital device and associated with a visual acuity size that is the same as the first visual acuity size, the second visual acuity size, or a third visual acuity size depending on the measured guess rate.

[0036] In one embodiment, the method comprises: d) further comprising monitoring the evolution of data relating to at least one refractive error of the user based on the evolution of the user's visual acuity value.

[0037] Advantageously, different visual acuity values ​​examined during the proposed method can be compared to obtain the evolution or recorded history of the user's visual acuity value over time. In particular, the proposed method allows obtaining data collected in accordance with the evolution of the user's visual acuity, such data being interpretable to estimate the positive and / or negative effects of various treatments, coefficients, etc., on the user's eye.

[0038] In one embodiment, steps b2.1), b2.2) and b2.3) are repeated through multiple iterations, and in each new iteration the first target size is replaced with either the same target size as the first target size, the second target size or the third target size depending on the guess rate measured in the immediately preceding iteration.

[0039] Advantageously, the proposed method adapts the visual acuity test to the user's performance in response to the displayed visual targets, thereby providing a modifiable and adaptable process for monitoring the user's visual acuity evolution and detecting, for example, any refractive errors, changes in eye correction, defocus.

[0040] In one embodiment, the iterations are performed under the following conditions: - the preset maximum number of iterations is met; and - replacing the first target size with the same target size for a predefined number of consecutive iterations; The process ends if at least one or a combination of the above is satisfied.

[0041] As a result, the duration of the monitoring phase of the myopia monitoring method may be flexible and may depend on the criteria and goals of the user. Such duration may be fixed, for example, by the maximum number of repetitions of the visual acuity test in case of myopia monitoring performed between two appointments with an ophthalmologist. Thus, the myopia monitoring is performed for a certain number of days, weeks, months so that the results of the myopia monitoring may be provided to the ophthalmologist. The myopia monitoring method may also aim to determine the exact visual acuity level of the user at different times and monitor its progression, for example, in case of the eye treatment the user follows and / or to monitor the myopia progression of the user's child. The visual acuity level may also be identified as accurate if the user's visual acuity is measured to be stable at such visual acuity level in a predefined number of visual acuity tests performed periodically.

[0042] The monitoring method may also be performed until the user schedules another appointment with the ophthalmologist.

[0043] According to one aspect of the present invention, the visual acuity reference value is: - displaying a plurality of successive targets at a plurality of successive corresponding target sizes; - measuring corresponding guess rates at each corresponding indicium size of the displayed indicium among the plurality of displayed indicia, where at least one guess rate is above a first guess rate threshold and at least one other guess rate is below a guess rate threshold; - identifying a displayed optotype, the corresponding guess rate corresponding to a guess rate threshold, the corresponding optotype size corresponding to an optotype reference size, and the visual acuity reference value relating to the corresponding optotype size; It is determined by carrying out the following.

[0044] As a result, the essence of the myopia monitoring process lies in a preliminary phase in which a visual acuity reference value is first determined. The determination of such a visual acuity reference value is carried out through multiple visual acuity tests. Advantageously, such a method allows obtaining an accurate value of the user's visual acuity without the need for complex equipment or an appointment with an ophthalmologist.

[0045] In one embodiment, displaying a plurality of successive indicia and measuring the corresponding respective guessing rates follows a predetermined period, said period being one or more days.

[0046] In one embodiment, any two consecutive corresponding indicia sizes have different values, and the ratio of such values ​​corresponds to a coefficient determined by a predetermined coefficient function, which may be a constant function that makes the coefficients equal.

[0047] Advantageously, the essence of determining the exact value of a user's visual acuity is to test several distinct values ​​of visual acuity in order to form an actual exact value of visual acuity.

[0048] In one embodiment, the visual acuity reference value is determined by performing an interpolation search over a number of successive optotypes displayed at a number of successive corresponding optotype sizes and corresponding guess ratios.

[0049] In fact, when the guess rate threshold is predefined and known, it is possible to determine, among a plurality of tested target sizes, a target size whose measured guess rate corresponds to the first guess rate threshold. The target size thus determined corresponds to a target reference value, and the corresponding visual acuity level is defined as a visual acuity reference value.

[0050] In one embodiment, the digital device is positioned by the user such that the displayed indicia is reflected in a mirror facing the user. The method then includes, before measuring and / or re-measuring the guess rate of the displayed indicia: and collecting ambient data relating to the current usage of the digital device, such ambient data including: the distance between the position of the digital device and the virtual image of the digital device created in the mirror by the reflection of the digital device; -Ambient light levels, and -Displayed targets and associated timestamps The present invention includes at least one or a combination of the above.

[0051] Additionally, the displayed indicia depend on the collected ambient data.

[0052] As a result, the monitoring method ensures accuracy of the results since successive vision tests are performed on the user under the same conditions and therefore the results of such vision tests are comparable.

[0053] Ambient data is understood to be data received from the man / machine interface of the digital device. The digital device used to perform the monitoring method may be equipped with a camera to assess the distance between the digital device and a reflective surface, such as a mirror, where the displayed optotypes are read by the user. The digital device may also be equipped with an ambient light sensor so that it may be possible to check the brightness of the light in the area where the vision test is performed. The user may also vocally express information about his position, the date and time, or any other information about the setup for performing the vision test, such information being collected and processed, for example, by voice recognition. Ambient data may also include the monocular or binocular nature of the monitoring.

[0054] The display of the visual symbol depends on the collected ambient data, which is understood to mean that the visual symbol displayed to the user with a predetermined visual symbol size (i.e. before starting the visual acuity test) depends on the digital device controlling that the detected, received and / or processed ambient data meets the setup conditions for performing the visual acuity test. Such setup conditions may be predefined as initialization data included in the application for myopia monitoring or may correspond to the ambient data collected in the first visual acuity test performed on the user. If such setup conditions are not met by the ambient data, the digital device may display a notice or a signal through the communication interface of the digital device to inform the user that the conditions for performing the visual acuity test are not met. For example, the digital device may display on the front screen of the digital device that the user is too far or too close to the mirror compared to the setup position or that the lighting is insufficient compared to the setup lighting. The digital device may also store in the memory unit the cycle to be followed between two visual acuity tests, and may inform the user to repeat the visual acuity test later if it is determined that the cycle is not followed compared to the last visual acuity test. If the ambient data is detected to meet the setup conditions (e.g., with a predefined error margin), the vision test may be initiated and the visual target is displayed by the digital device.

[0055] In one embodiment, at a first time, a visual acuity reference value and a target reference size are determined, at a second time, a target displayed at a first target size and a measured guessing ratio are identified, and at a third time, a target displayed at a second target size and a re-measured guessing ratio are identified. In that case, at least one storage memory is provided, - data relating to the visual acuity reference value and / or the optotype reference size is stored in the storage memory in correspondence with the data at the first time; - data relating to the first target size and the measured guess rate are stored in the storage memory in correspondence with the data at the second time; - data relating to a second target size and the remeasured guessing rate is stored in the storage memory in correspondence with the data at the third time; The data is further stored corresponding to the user's identifier.

[0056] As a result, the method allows each vision test to be time-stamped, along with the circumstances of the vision test and an identifier for the user, such that all data relevant to the method is recorded and arranged so that such data may, for example, be formatted for transmission to other devices for interpretation for further processing.

[0057] In one embodiment, said storage memory stores data of a database and is accessible by at least one terminal through a communication network, thereby providing at least a history of the evolution of said visual acuity value to a user of said terminal.

[0058] In one embodiment, the output data of the digital device is, for a given user, - visual acuity reference value, - the selected target size of the displayed target, and - Guessing rate of the displayed stimulus Including, The digital device is connected to a communications network and is configured to transmit said output data via said communications network to a remote server.

[0059] As a result, the results of the myopia monitoring and the continuous vision test are registered to be transmitted, interpreted, and accessed via the storage memory. Such a storage memory may be supported by a server on the digital platform via the cloud or by the digital device. Thus, for each user who monitors his / her vision via the monitoring method, data related to the user's vision progress may be consulted and interpreted, for example, by the user's ophthalmologist, the user's parents, the user's optician, or any relevant eye care professional (or ECP). Such an ECP may also rely on the data generated from the proposed method to establish a diagnosis of the user's eye. The database of the storage memory may be updated with the data transmitted by the digital device, for example, in real time, after the vision test is completed, or when the monitoring phase is over. Thus, the database may centralize the data related to the myopia monitoring of multiple users, and the eye care history of each user may be consulted by a request performed on the database using the user's identifier.

[0060] The results of the monitoring method can thus be integrated with the information and knowledge of the eye care professional to obtain a complete and exhaustive eye care history (or record) of the user. The server can also process the data stored in the storage memory to obtain the myopia evolution curve of the user and to establish statistical metrics for the efficiency of a particular eye treatment or for example for the progression of myopia in children.

[0061] A user of a terminal is understood as any individual or organization that is interested in obtaining or viewing the results of a user's myopia monitoring via such a terminal. Such a user of a terminal may correspond to the user himself (i.e. the user performing the myopia monitoring), the user's parents, an ophthalmologist, or any eye care professional (ECP) to view the user's own results. A terminal may refer to a digital device of the user of the terminal, such as a computer or a mobile device, for example.

[0062] Other features, details and advantages are set forth in the following detailed description and figures, without limitation. [Brief description of the drawings]

[0063] [Figure 1] 1 represents a schematic use of a digital device for testing a user's visual acuity value. [Diagram 2] 1 depicts a flowchart showing steps for visual acuity testing of a user using a digital device. [Diagram 3] 1 depicts a flowchart showing steps of a preliminary phase of determining a visual acuity reference value. [Figure 4] Figure 1 shows the evolution of guess rates for two individuals as a function of target size. [Diagram 5] 4 depicts a flow chart illustrating steps of a monitoring phase according to one embodiment of the present invention; [Figure 6] 4 illustrates the results of a myopia monitoring process according to one embodiment of the present invention. [Figure 7] 1 illustrates a digital device according to one embodiment of the present invention. [Figure 8] 1 illustrates a system for transmitting results of myopia monitoring according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0064] Reference is now made to Figure 1. Figure 1 depicts a setup for periodically testing the visual acuity of a user 1 of the setup using a digital device 2 and a reflective surface, such as a mirror 3, which is flat.

[0065] The digital device 2 refers to a portable computing device that can be used independently and is small enough to be easily carried and operated by the user 1 by hand. Such a digital device 2 may refer to, for example, a smartphone, a phablet, or a tablet. As shown in FIG. 7, the digital device 2 comprises at least a processing unit PROC, a memory unit MEM, and an output communication unit COM with at least a screen. More generally, the digital device 2 comprises a processing circuit including a processing unit PROC. The processing circuit includes a computer program product, which includes program instruction codes stored in a computer-readable medium of the product, whereby the digital device 2 is capable of performing the steps of testing the visual acuity of the user 1 and monitoring the progress of such visual acuity, as will be further detailed in the description.

[0066] The output communication unit COM may also comprise a speaker. The digital device 2 also comprises a man / machine interface INT, so that the digital device 2 can collect data received from the user 1 and from the environment around the digital device 2. Such a man / machine interface INT may include one or several of the following elements: a voice recognition module, a gesture and / or image recognition module (e.g. via a camera), a front camera 20, a physical switch of the digital device 2 pressed by the user 1 (e.g. plus and minus volume switches, etc.), a tactile surface. The screen and the front camera 20 of the digital device 2 may be located on the same side of the digital device 2. The digital device 2 also comprises communication means, so that the digital device 2 can emit and / or receive radio frequency signals to and / or from devices and other equipment in the environment around the digital device 2. For example, the digital device 2 can communicate via Bluetooth, Wi-Fi, and / or 3G / 4G / 5G protocols.

[0067] Reference is now made to Figure 2, which illustrates the successive steps of carrying out a visual acuity test for a user 1 of a digital device 2 using such a digital device 2.

[0068] A user 1 may first proceed to a user positioning step E1 in order to test his / her visual acuity. During the user positioning step E1, the user 1 of the digital device 2 positions himself / herself in front of the mirror 3 at a predefined distance D from the mirror 3. As shown in FIG. 1, the user 1 is positioned at a predefined distance D facing the mirror 3 to see a virtual image 2', 21' generated by light reflected at the surface of the mirror 3. The mirror 3 is a plane mirror. When the user 1 is positioned at the predefined distance D, the distance between said user 1 and the virtual image that the user 1 sees in the mirror 3 can be defined as being equal to twice the predefined distance D. According to an embodiment, the predefined distance D is equal to or greater than 1.5 meters, preferably equal to or greater than 2.0 meters. Advantageously, the predefined distance D is equal to or greater than 2.5 m for better relaxed accommodation. In such conditions, the visual acuity test evaluates the visual acuity of the user 1 with respect to distance vision. Alternatively, the predefined distance D may be equal to or less than 0.5 m, preferably equal to or greater than 0.25 m. Under such conditions, the vision test evaluates the vision of the user 1 with respect to near vision. In the context of the present description, the vision measurement is performed with respect to myopia monitoring. Thus, the vision of the user 1 is tested with respect to distance vision.

[0069] The user 1 may then proceed to a step E2 of positioning the digital device 2. During the step E2 of positioning the digital device 2, the user 1 positions the digital device 2 such that the screen of the device 2 faces the mirror 3. Preferably, the digital device 2 is positioned vertically so as to be substantially parallel to the plane of the mirror 3. In one embodiment, the digital device 2 may be positioned over one eye of the user 1, as represented in FIG. 1, and the visual acuity of the other eye (i.e. the eye not covered by the digital device 2) is assessed. Advantageously, such positioning of the digital device 2 facilitates the assessment of the monocular visual acuity of the user 1.

[0070] The vision test then comprises a distance measurement step E3, during which a distance d between the front camera 20 of the digital device 2 and the virtual image 2' of the digital device 2 is measured. Such a distance d may be measured by the digital device 2 itself.

[0071] The vision test then includes a digital device data processing step E4, during which data relating to the digital device 2 is collected. Such data relating to the digital device 2 may include data relating to the physical size of the digital device 2 and camera data relating to at least the angular resolution of pixels of the front camera 20'. The physical size of the screen of the digital device 2 may be w s ×h s It can be expressed as w s is the physical screen width, and h s is the height of the physical screen. Such a physical size is determined by the screen resolution m s ×n s (m s is the screen width in pixels, and n s is the height of the screen in pixels) and the pixel density of the screen D p,s The screen resolution and pixel density can be easily obtained from the mobile device's operating system (OS) or manufacturer data. s , n s , and D p,s Knowing the value of w, we can use the following formula: s and h s A value of can be specified. [Number 1]

number

[0072] As a non-limiting example, the calculation of the physical size of the screen of a mobile device 2 is based on a screen resolution m equal to 1440x3040. s ×ns and pixel density D equal to 550 dpi p,s The example is illustrated for a particular smartphone having a screen size of 140.4 mm. Using the formula [1], we obtain a screen width ws equal to 66.5 mm and a screen height ws equal to 140.4 mm. Alternatively, the screen size can be calculated from the screen diagonal physical size and the resolution.

[0073] Pixels of the front camera 20' c,θ The angular resolution of the front camera is determined by the pixel size p c and focal length f c Similarly, the pixel size and focal length of the front camera 20' can be obtained from the operating system (OS) of the digital device or from manufacturer data. c and f c By knowing the value of p c,θ can be determined using the following formula: [Number 2]

number

[0074] As a non-limiting example, the calculation of the angular resolution of pixels of the front camera 20′ of the mobile device 2 can be done by multiplying the pixel size p c The example is illustrated for a particular smartphone with a focal length of 3.34 mm and a resolution of 1.22 μm. Using equation [2], the angular resolution p of the pixels of the front camera 20 is equal to 0.021 degrees. c,θ Get the.

[0075] For simplicity, let us assume that the physical size of the camera pixel is p c is assumed to have the same value in the horizontal and vertical directions. However, the reasoning can be easily extended if this condition is not true. In another embodiment, the specified working distance of the front camera 20 is likely not set to infinity, so the value f ccan be replaced by the actual distance between the lens and the camera sensor of the digital device 2. Alternatively, the actual distance between the lens and the camera sensor can be calculated by assuming that the camera is set at a finite distance between 0.5 m and 1.0 m, preferably 0.8 m.

[0076] The distance d between the front camera 20 of the digital device 2 and the virtual image 2' created by the mirror 3 in which said digital device 2 is reflected can be measured based on data related to the digital device 2. To that end, the processor PROC of the digital device 2 may collect data captured from the front camera 20. Typically, the front camera 20 of the digital device 2 captures images and / or videos of the mirror and of the virtual image 2' formed by the mirror 3 facing the front camera 20. The images and / or videos may be further processed to extract data related to the size of the virtual image 2' of the screen of the digital device 2 reflected by the mirror 3. For example, the width of the screen of the virtual mobile device 2' reflected by the mirror may be determined based on the number of pixels m on the photo / video recorded by the front camera 20. c,d Similarly, the height of the screen of the virtual mobile device 2′ reflected by the mirror 3 can be expressed as the number of pixels n on the photo / video recorded by the front camera 20. c,d Then, the distance d between the front camera 20 of the digital device 2 and the virtual image 2′ generated by the mirror 3 can be determined using the following equation: [Number 3]

number

[0077] Alternatively, the distance d can be measured by displaying different shapes of known predefined dimensions on the screen of the digital device 2. Knowing the dimensions of the displayed shapes, the distance d can be measured using Equation 2 and Equation 3.

[0078] The vision test may also include a distance control step E5, during which the distance d measured between the front camera 20 of the digital device 2 and the virtual image 2' created by the mirror 3 is compared with a predefined distance D.

[0079] The vision test may further comprise a notification step E6. During the notification step E6, a notification is sent by the digital device 2 to the user 1 based on a comparison of the measured distance d with a predefined distance D. For example, if the measured distance d between the front camera 20 of the digital device 2 and the virtual image 2' created by the mirror 3 is smaller than the predefined distance D, the notification may indicate that the user 1 is too close to the mirror 3. For example, if the measured distance d between the front camera 20 of the digital device 2 and the virtual image 2' created by the mirror 3 is larger than the predefined distance D, the notification may indicate that the user is too far away from the mirror. Alternatively, a maximum deviation ΔD from the value of the predefined distance D may be defined. If the measured distance d is smaller than (2D-ΔD), the notification may indicate that the user 1 is too close to the mirror 3. Similarly, if the measured distance d is larger than (2D+ΔD), the notification may indicate that the user 1 is too far from the mirror 3. The maximum deviation ΔD may correspond to a variation of the predefined distance D of 20%, preferably 10%, more preferably 5%.

[0080] The visual acuity test further comprises a display step E7. Preferably, the display step E7 is performed after the distance control step E5 and the notification step E6. During the display step E7, the optotypes are displayed on the screen of the digital device 2. In the sense of the present disclosure, optotypes refer to standardized symbols commonly used to test a person's visual acuity.

[0081] As shown in FIG. 1, the visual symbols displayed on the screen of the digital device 2 are reflected by a mirror 3 which generates a virtual image 21′ of the visual symbol. Preferably, symmetry is applied to the displayed visual symbols so that the orientation of the visual symbols displayed on the screen of the digital device 2 and seen by the user 1 is similar. Advantageously, the user 1 will perceive the virtual image 21′ of the displayed visual symbol in the correct orientation. The displayed visual symbols may be Landolt C or Snellen E, or other standardized visual symbols, letters or figures. The visual symbols may be displayed one by one (i.e. consecutively) on the screen of the digital device 2 during the display step E7. Alternatively, the visual symbols may be displayed row by row with multiple visual symbols in each row. The size and / or orientation and / or contrast of each visual symbol may be changed during the display step. Alternatively, multiple rows of visual symbols may be displayed simultaneously, with each row displaying visual symbols of different size and / or orientation and / or contrast, for example an ETDRS chart-like or two rows of the Essilor VR-800 procedure. Alternatively, the displayed indicia may correspond to words or short sentences.

[0082] During the display step E7, the size of the displayed object (called "object size") may be adapted based on the measured distance d. Alternatively, the size of the displayed object may be determined based on a predefined distance D from the mirror 3. Similarly, the angular size (or detail size) of the object displayed on the screen of the digital device 2 may be adapted based on the measured distance d.

[0083] As a non-limiting example, as depicted in Figure 1, the visual target considered for the following calculations is a Landolt ring with an aperture such that the virtual image 2' at a distance d of the displayed digital device 2 of the Landolt ring has an angular size Δθ. The physical size Δs of the aperture as displayed on the screen is given by the following formula: [Number 4] Δs = d × tan(Δθ)

[0084] For example, if the measured distance is 4.0 m, the aperture Δθ of the Landolt ring displayed for 10 / 10 visual acuity should be equal to 1'. By using the formula [Equation 4], the physical size Δs of the aperture displayed on the screen is approximately equal to 1.16 mm. Referring to a specific smartphone as an example, the physical size Δs of the aperture displayed on the screen is equal to 1.16 mm, which is calculated by multiplying the number of pixels (Δs / p s ) is approximately equal to 25 pixels on the screen.

[0085] 1, the displayed target 21' may include a single Landolt C, with the gaps of the Landolt C oriented randomly in one of several predefined directions. Such predefined directions may refer, for example, to the four cardinal directions (North N, South S, East E, and West W) and / or the eight cardinal directions (Northeast, Southeast, Northwest, and Southwest).

[0086] According to an embodiment of the present disclosure, the distance d between the front camera 20 and the mirror 3 is measured frequently during the display step. For example, the distance d can be measured before displaying a different target or a series of targets. Preferably, the distance d between the front camera 20 and the mirror 3 is measured in real time. Advantageously, the size and / or the angular size of the target displayed on the screen of the digital device 2 can be updated periodically, for example in real time, thereby providing a more accurate test of the user 1's visual acuity.

[0087] The vision test further comprises an evaluation step E9, during which the correctness of the tested vision of the user 1 is evaluated.

[0088] The method for evaluating the accuracy of the visual acuity tested on the user 1 may further comprise a response receiving step E8 before the evaluation step E9. During the response receiving step E8, a response or instruction (more generally, input data) is received from the user 1 in response to the display of each optotype. Such input data may be received by the digital device 2 via the man / machine interface INT. The input data of the user 1 may be received using voice recognition, gesture recognition, and / or a movement of the mobile device. If the optotypes displayed on the screen of the digital device 2 are words or short sentences, the user 1 may identify the letters or read the sentences. These instructions received from the user 1 may be obtained, for example, using voice recognition via the microphone of the digital device 2. If the optotypes displayed on the screen of the digital device 2 are Landolt C with different opening directions, as shown in FIG. 1, the user 1 may indicate the opening direction that he recognizes. The indication regarding the direction of the aperture perceived by the user 1 may be obtained by voice recognition using the microphone of the digital device 2, by a mobile device motion using the IMU of the digital device 2 or the front camera of the digital device 2, and by a head motion and / or an arm motion using the front camera of the digital device 2. The digital device 2 may further comprise physical plus ("+") and minus ("-") volume buttons 22a and 22b. Preferably, the plus volume button 22a and the minus volume button 22b are located on the side of the digital device 2. The plus volume button 22a and the minus volume button 22b may be used by the user 1 to provide an indication during the response receiving step. Such use of a physical switch of the digital device 2 is particularly advantageous when the displayed visual indicator is a Landolt C type with an aperture in different directions. Such a displayed visual indicator may include, for example, a movable cursor. The movable cursor may be, for example, a circular art that moves along the different possible directions of the aperture of the Landolt C. In such a case, the user 1 can utilize the physical plus and minus buttons 22a and 22b of the digital device 2 to align the direction of the movable cursor with the perceived opening of the Landolt C.The selected position of the cursor may then be enabled after a short waiting period, for example 0.5 to 2.0 seconds, preferably after a waiting period of 1.0 second.

[0089] The accuracy of the visual acuity tested at user 1 may be assessed during an evaluation step E9 based on the target size of the targets displayed during the display step E7 and on the instructions received from user 1 during the response receiving step E8.

[0090] Indeed, during the display step E7, a first series of different randomized visual symbols, for example corresponding to the same first visual acuity level, is presented to the user 1. The essence of such display of the first series of visual symbols may consist in successively displaying a predefined number of visual symbols within the first series of visual symbols with a first visual acuity level corresponding to the first visual acuity level. Such visual symbol size (and / or such first visual acuity level) being recorded in the memory unit MEM of the digital device 2. For each displayed visual symbol, the digital device 2 may receive input data from the user 1 through the man / machine interface INT, indicating the visual symbol guessed by the user 1. For example, with reference to FIG. 1, the correct response (or instruction) is the Landolt C gap displayed oriented in the West W direction. Such input data is collected in a response receiving step E8 for each displayed visual symbol of the first series of visual symbols displayed during the display step E7. During an evaluation step E9, the instructions received from the user 1 are evaluated and a score corresponding to the correctness of the instruction may be given to the user 1. Such a score, also referred to as a "guessing rate," is particularly associated with a first object size of the displayed object and, therefore, a first visual acuity level.

[0091] In the context of this description, the visual acuity of the user 1 may quantify the ability of the user 1 to distinguish the smallest possible details with satisfactory accuracy, where satisfactory accuracy is defined as the ability to guess a displayed detail (typically the target size) at a considered size (typically the target size) with a percentage of correct answers, also called "score" or "guessing rate", equal to the guessing rate threshold (THS). There is then a direct existing correspondence between visual acuity and the target size of the displayed target, and such correspondence depends in particular on the distance at which such target is displayed to the user 1. Thus, since the target size is associated with a unique visual acuity level, a distance d that is periodically checked to be constant, a test at a given target size, or a test at a given visual acuity level can be understood synonymously. The target size of the displayed target (in other words the visual acuity level) is controlled by the digital device 2, which measures the guessing rate of the user 2 in response to the target being displayed at such target size.

[0092] The guessing rate of user 1 when the optotype 21' is displayed at the optotype size can be defined by the ratio (in other words, the percentage) of the number of optotypes that user 1 can guess correctly to the total number of optotypes displayed. For example, if the guessing rate of user 1 is equal to 1 (i.e., 100 percent), user 1 is able to undoubtedly identify the optotype displayed at the tested optotype size, and the visual acuity corresponding to such a tested optotype size is considered to be lower than user 1's actual visual acuity (in fact, user 1 may be able to identify the optotype at a size smaller than the tested optotype size). The guessing rate of user 1 is considered to be minimum when user 1 is unable to guess the displayed optotype 21' except by random guessing. Thus, the minimum guessing rate is the probability of randomly guessing the correct optotype. Thus, for a Landolt C with eight different positions, the minimum guessing rate is 1 / 8, or 12.5 percent.

[0093] The guessing threshold THS may be a value approximately equal to 50% to 70%, preferably 60 percent. In one embodiment, visual acuity may also be defined as the ability to guess the displayed optotype 21' at the considered optotype size with a guessing rate approximately corresponding to the guessing rate threshold THS by a tolerance value ε. Such a tolerance value ε may be 5 percent to 15 percent. As a result, if the guessing rate of the displayed optotype of the user 1 is approximately equal to the guessing rate threshold THS (or differs from the guessing rate threshold THS by a gap not exceeding the tolerance value ε), the optotype size of the optotype displayed during the visual acuity test can be considered as the minimum size of the detail that the user 1 can correctly perceive. The visual acuity level associated with such optotype size is then determined as the visual acuity of the user 1 during the visual acuity test.

[0094] In another embodiment, the essence of the setup for testing the vision of user 1 may be a digital device 2 corresponding to a computer. Such a computer may include a screen facing user 1 and displaying visual objects directly to user 1. User 1 then responds to the displayed visual objects by expressing responses by voice or typing, such responses being recorded by the computer. The process may take place in the context of a virtual appointment with an ophthalmologist.

[0095] In alternative embodiments, the visual acuity of user 1 may be assessed using alternative methods. Preferably, the visual acuity of user 1 is assessed using a self-measurement method.

[0096] The visual acuity test shown in Fig. 1 and Fig. 2 allows a user 1 to test a certain visual acuity value, more specifically the accuracy of such visual acuity, using a self-measurement method together with a digital device 2. With the visual acuity test, a selected (or tested) visual acuity value (and thus a selected visual acuity size) is tested on the user 1 by displaying a series of optotypes at such selected visual acuity size. Such a tested visual acuity value may be an accurate value of the visual acuity of the user 1 at the time the visual acuity test is performed. It is reflected in particular in a guess rate that approximately corresponds to the guess rate threshold THS. If the guess rate calculated during the evaluation step E9 still differs significantly from the guess rate threshold THS (e.g. the gap between the calculated guess rate and the guess rate threshold THS exceeds the tolerance value ε), the tested visual acuity is considered to be inaccurate.

[0097] In order to monitor the time evolution of refractive errors such as myopia, the essence of the proposed method is to monitor the evolution of the visual acuity value of user 1, assuming that the evolution of the refractive errors of user 1 is reflected in the evolution of the visual acuity value of user 1. The proposed method particularly relies on performing several visual acuity tests to assess a selected visual acuity value of user 1. To test a selected visual acuity value of user 1, the visual acuity tests described in Figs. 1 and 2 may be applied. Alternatively, other existing methods of estimating values ​​related to the visual acuity of user 1 may be applied. The Stanford Visual Acuity Test (i.e. StACT) or the Freiburg Visual Acuity Test (FrACT) are examples of such existing methods.

[0098] The essence of the proposed method for assessing the progress of the visual acuity of a user 1 lies in two distinct phases: a preliminary phase PP and a monitoring phase MP. A detailed application of the proposed method is shown in FIG.

[0099] The essence of the preliminary phase PP is to determine the exact value of the visual acuity of the user 1 at a given time, and such exact value of the visual acuity is called the "visual acuity reference value" VA_ref. Such a preliminary phase PP is detailed in Figures 3 and 4.

[0100] The essence of the monitoring phase MP then consists in monitoring the evolution over time of the visual acuity value of user 1 with respect to the visual acuity reference value VA_ref. Such a monitoring phase MP is detailed in FIG.

[0101] In particular, such a monitoring phase provides data that allows monitoring the evolution of the refractive error of the user 1, such as myopia. Indeed, if the determined value of the correct visual acuity of the user 1 decreases over time compared to the visual acuity reference value VA_ref, this means that the myopia of the user 1 has progressed over time (leading to worsening of myopia). If the determined value of the correct visual acuity of the user 1 is generally close to the visual acuity reference value VA_ref over time (e.g., the gap is smaller than the tolerance value ε), this means that the myopia of the user is stable over time. In less common cases (e.g., in the case of the assessment of a specific myopia treatment), if the determined value of the correct visual acuity of the user 1 increases over time compared to the visual acuity reference value VA_ref, this means that the myopia of the user 1 has recovered over time (leading to improvement of myopia). Furthermore, based on the number of repetitions of the visual acuity test performed and the potential fluctuation of the visual acuity value over time, the data generated from the monitoring phase MP may be interpreted to evaluate the progression of various eye diseases and / or the effectiveness of various eye treatments.

[0102] Reference is now made to Figure 3, which is a flow chart illustrating the steps of determining the visual acuity reference value VA_ref of user 1 during the preliminary phase PP of the myopia monitoring process based on measurements of guess rates of different visual acuity tests at different visual acuity levels. With respect to the following figures, consider that the guess rate threshold THS is predefined at 60 percent and the tolerance value ε is predefined at 10 percent.

[0103] In step S0a, an initial value (or level) of visual acuity VA1.1 is tested on the user 1. Such visual acuity value VA1.1 is chosen to be, for example, less than 1.0 (i.e., less than 10 / 10). Such visual acuity level VA1.1 corresponds to a series of visual symbols 21' displayed by the digital device 2 with an initial visual symbol size OS1.1. For example, 10 random visual symbols with the same visual symbol size OS1.1 are displayed consecutively on the screen of the digital device 2, such visual symbols being, for example, Landolt C visual symbols with gaps oriented randomly among eight directions (four orientations and eight orientations). In other embodiments, the series of visual symbols displayed may include more or less than ten visual symbols. At each display, the response of the user 1 is received via the human interface machine INT of the digital device 2. After the ten symbols are displayed with the symbol size OS1.1, a guessing ratio X1.1 is identified corresponding to the initial symbol size OS1.1 (and thus the initially tested visual acuity level VA1.1). In step S0b, such guessing ratio X1.1 is checked to be above the guessing ratio threshold THS, and if not, a lower initial visual acuity level VA1.1 is tested (with a larger symbol size 1.1 compared to the tested symbol size OS1.1). In one embodiment, the guessing ratio X1.1 is checked to be above the guessing ratio threshold THS by a tolerance value ε. In other words, the guessing ratio X1.1 is checked to be above 70 percent. In fact, the aim is to start the visual acuity test of the first user 1 at an initial visual acuity level lower than the user 1's correct visual acuity (also called visual acuity reference value VA_ref, which is still unknown). Both the initial symbol size OS1.1 and the corresponding guessing ratio X1.1 are then stored in the memory unit MEM of the digital device 2 corresponding to the time of the initial visual acuity test.

[0104] In step S1.1a, a new visual acuity level VA1.2, which is higher than the initial visual acuity VA1.1, is tested on the user 1. Such step S1.1 may be performed several days or one week after steps S0a and S0b. Such a new visual acuity level VA1.2 is tested through a series of visual targets displayed by the digital device 2 with a visual target size OS1.2 smaller than the initial visual target size OS1.1. The visual acuity level VA1.2 (in other words, the visual target size OS1.2) can be determined based on the initial visual acuity level VA1.1 (in other words, the initial visual target size OS1.1) and a predefined coefficient function f, such that VA1.2=f(VA1.1). In one embodiment, such coefficient function can be a constant function equal to α (α>1). In other words, a predefined coefficient function g can be applied to the visual target size OS1.1 to obtain a new visual target size (OS1.1)=OS1.2 to be tested, and such a new visual target size OS1.2 is smaller than the visual target size OS1.1.

[0105] Such a visual acuity test with the displayed target at target size OS1.2 generates a measured new guess rate X1.2. In particular, such measured new guess rate X1.2 is equal to or less than the previous guess rate X1.1. Indeed, it is assessed that for the myopic user 1, lowering the target size (equivalent to raising the visual acuity level) leads to a lower guess rate. The guess rate X1.2 is determined corresponding to the target size OS1.2 (and thus the tested visual acuity level VA1.2). In step S1.1b, such guess rate X1.2 is compared with β*THS, where β is a predefined coefficient less than or equal to 1. If such guess rate X1.2 exceeds β*THS, the test step S1.1a and the comparison step S1.1b are repeated with a new visual acuity level better than the visual acuity level VA1.2 (in other words a target size smaller than the target size OS1.2), which is determined based on a predefined coefficient function f (in other words based on a predefined coefficient function g), as mentioned. Both the indicium size OS1.2 and the corresponding guess rate X1.2 are stored in the memory unit MEM of the digital device 2, as are the subsequent values ​​of the indicium size and the corresponding guess rates.

[0106] In iteration n (n is an integer equal to or greater than 1), a series of displayed targets with target size OS1.n generates a guess rate X1.n in step S1.2a, and if such determined guess rate X1.n is less than β*THS in S1.2b, the iteration stops. Indeed, if the condition X1.n<β*THS is met in step S1.2b, it is guaranteed that the process of FIG. 2 has been repeated a sufficient number of times (here n times) to constrain the guess rate threshold THS between the two guess rates corresponding to the two distinct target sizes OS1.1 and OS1.n. That is, the guess rate threshold THS is included in the interval between the initial guess rate X1.1 and the guess rate X1.n, where both guess rates X1.1, X1.n correspond to target sizes OS1.1, OS1.n. Based on the assumption that for myopic user 1, the guessing rate decreases when the size of the displayed object is reduced, the process allows the object size for which the guessing rate corresponds to the guessing rate threshold THS to be constrained between object sizes OS1.1 and OS1.n. In another embodiment, the stopping condition in step S1.2b also includes one or a combination of the following elements: - a fixed number of repetitions of the visual acuity test; the gap between the guess rate and the guess rate threshold THS exceeds a tolerance value ε; - The guess rate is less than the guess rate threshold THS (in this case β=1).

[0107] Thus, the essence of steps S0a, S0b, S1.1a, S1.1b, S1.2a, S1.2b is to initialize a process of determining a visual acuity reference value VA_ref having a target size OS1.1 at which the guess rate exceeds the guess rate threshold THS, and then repeat steps S1.1a and S1.1b while decreasing the value of the visual acuity size until the guess rate is sufficiently lower (i.e., by a difference of, for example, the coefficient β) than the guess rate threshold THS.

[0108] Therefore, in step S2, it is possible to identify an estimate of the target size whose guess rate strictly corresponds to the guess rate threshold THS, and such target size is called target reference size OS_ref. In particular, such target reference size OS_ref is included between target sizes OS1.1 and OS1.n, since the guess rate threshold THS is included between the guess rates X1.1 and X1.n. During the process, if the guess rate threshold THS is reached (i.e., during the iterative process, the displayed target of target size OS1.x leads to a guess rate corresponding to the guess rate threshold THS), the target reference size OS_ref can be directly identified as the target size OS1.x whose displayed target was guessed with a guess rate equal to the guess rate threshold THS. In order to identify the target size OS1.x whose guess rate strictly corresponds to the guess rate threshold THS, a search algorithm such as an interpolation search or a binary search may be applied between the target sizes OS1.1 and OS1.n. In another embodiment, in step S2, a target reference size OS_ref is selected from the target sizes OS1.x of the displayed targets, the gap between the corresponding guess rate X1.x and the guess rate threshold THS is less than the tolerance value ε. In such a case, when multiple target size values ​​fit the target reference size OS_ref, the median or average of such multiple values ​​can be determined as the target reference size OS_ref.

[0109] In step S3, such target size OS1.x is then defined as a target reference size OS_ref, and the visual acuity level corresponding to such target size OS1.x is defined as a visual acuity reference value VA_ref of user 1.

[0110] The process of FIG. 3 is applied as an example to produce the curves of FIG.

[0111] FIG. 4 represents the evolution of the guessing rate of two different users 1 depending on the optotype size of the optotype 21' displayed to each user 1. The first curve C1 corresponds to the evolution of the guessing rate of the first user 1 for the displayed optotype 21' and the second curve C2 corresponds to the evolution of the guessing rate of the second user 2 for the same displayed optotype 21'. The display and measurement of both users 1 can be performed in similar conditions, for example according to the setup of FIG. 1 and the visual acuity test of FIG. 2. Both users 1 have the same positioning relative to the mirror 3, the predefined distance D is the same, the time (or at least the frequency) of the measurements and the lighting conditions are similar. The iterative process of FIG. 3 is considered to stop for user 1 when the guessing rate of user 1 is strictly less than β*THS, β=1 / 3 and THS=0.6 (or 60 percent). In other words, the iterative process stops when the guessing rate X1.x is strictly less than 0.2 (or 20 percent).

[0112] At an initial time T0, the same set of targets is displayed to both users 1 with the same initial target size OS1.1=2.25 arcmin. Based on the data input of users 1 received from the digital device 2, it is determined that both the first and second users 1 have the same guess rate X1.1=1 (or 100 percent). Since such guess rate X1.1 exceeds the guess rate threshold THS (considered to be 0.6 or 60 percent), the searched target reference size OS_ref for both users 1 is determined to be 1. user 1 , OS_ref user 2It is ensured that OS1.1=2.25 is less than OS1.1=2.25. At time T1 later than time T0 (e.g., several days or one week after time T0), a new set of targets is displayed to both users 1 with the same target size OS1.2=1.50 arcmin, which corresponds to a higher visual acuity level compared to the initial visual acuity level tested at time T0. Such target size OS1.2 may be calculated by the processing unit of the digital device 2 based on the initial target size OS1.1 and a predefined coefficient function g (defined here as a constant function g). At target size OS1.2=1.50 arcmin, the first user 1 and the second user 1 have different guess rates. As shown by the first curve C1, the first user 1 has a guess rate X1.2 approximately equal to 1 (or 100 percent). user 1 while a second user 1 has a guess rate of 0.9 (or 90 percent) X1.2 user 2 Both guess rates are x1.2 user 1 , X1.2 user 2 exceeds β*THS=20 percent, the process is repeated at time T2. At time T2, which is later than time T1, a new set of objects is displayed to both users 1 with the same object size OS1.3=g(OS1.2)=1.25 arcmin. At object size OS1.3=1.25 arcmin, the first user 1 and the second user 1 have different guess rates. As shown by the first curve C1, the first user 1 has a guess rate X1.3 approximately equal to 0.92 (or 92 percent). user 1 while a second user 1 has a guess rate of 0.6 (or 60 percent) X1.3 user 2 Both guess rates are x1.3 user 1 , X1.3 user 2 exceeds β*THS=20 percent, the process is repeated at time T3. At time T3, which is later than time T2, a new set of objects is displayed to both users 1 with the same object size OS1.4=g(OS1.3)=1.00 arcmin. At object size OS1.4=1.00 arcmin, the first user 1 and the second user 1 have different guess rates. As shown by the first curve C1, the first user 1 has a guess rate X1.4 approximately equal to 0.60 (or 60 percent).user 1 while a second user 1 has a guess rate of 0.30 (or 30 percent) X1.4 user 2 Both guess rates are x1.4 user 1 , X1.4 user 2 Since g(OS1.4) exceeds β*THS=20 percent, the process is repeated at time T4. At time T4, which is later than time T3, a new set of symbols is displayed to both users 1 with the same symbol size OS1.5=g(OS1.4)=0.50arcmin. At symbol size OS1.5=0.50arcmin, the first user 1 and the second user 1 have the same guess rate X1.5, which is equal to 0.125 (or 12.5 percent). It can be noted that such a guess rate X1.5=0.125arcmin corresponds to the probability of randomly guessing the correct symbol. Therefore, at symbol size OS1.5=0.50arcmin, both users 1 are a priori unable to actually identify the displayed symbol, meaning that they guessed the displayed symbol completely randomly. Since the guess rate X1.5 falls below β*THS=20 percent, the iterations stop.

[0113] Note that in the example of FIG. 4, the guess rate threshold THS=60 percent is reached with a target size OS1.4=1.00 for the first user 1 and with a target size OS1.3=1.25 for the second user 1. Therefore, no search algorithm is needed and the target reference size for the first user 1 is of_ref user 1 = 1.00, and the second user 2's visual reference size is OS_ref user 2 In the process, considering that the same accuracy (general guess rate threshold THS) is required under similar test conditions, it is determined that the first user 1 is capable of distinguishing small details (here, details of 1 arcmin) compared to the second user 1 (here, details of 1.25 arcmin). Therefore, in particular, at the reference time T4, the visual acuity reference value VA_ref user 1 is the visual acuity reference value VA_ref of the second user 1 user 2 Note that this exceeds

[0114] The value of the predetermined function f, the value of the predefined function g, and the value of the predefined coefficient β are preset values. The values ​​provided in the description of Figures 3 and 4 are non-limiting examples. In particular, by adopting such values, the search for the visual acuity reference value VA_ref can be more or less accurate, since more or fewer measurements are performed.

[0115] In another embodiment, the determination of the visual acuity reference value VA_ref may be generated from an appointment with an eye professional such as an ophthalmologist, where user 1's visual acuity level is identified at the time of the appointment and such visual acuity level is considered to be user 1's visual acuity reference value VA_ref when the monitoring phase MP is initiated.

[0116] Reference is now made to FIG. 5. FIG. 5 is a flow chart representing steps of a process of monitoring the visual acuity value of user 1 over time (reflecting the evolution of refractive errors such as myopia) during a monitoring phase MP. The essence of such a monitoring phase MP is to evaluate the possible evolution of the visual acuity of user 1 from his visual acuity reference value VA_ref. Such visual acuity reference value VA_ref is determined at a time before the start of the monitoring phase MP, for example during a preliminary phase PP as described in FIG. 3. For example, the monitoring phase MP is started one week after the determination of the visual acuity reference value VA_ref during the preliminary phase PP. The test conditions of the visual acuity test during the preliminary phase PP are applied to the visual acuity test during the monitoring phase MP. The surrounding environment of user 1 and the conditions of use of the digital device 2 for performing the visual acuity test are considered to remain the same. The guess rate threshold THS is considered to be set at 60 percent and the tolerance value is considered to be set at 10 percent. In particular, guess rate values ​​comprised between 50 percent and 70 percent of correct responses are considered to match the guess rate threshold THS. Unless otherwise specified, a "guessing rate corresponding to the guessing rate threshold THS" or a "guessing rate approximately equal to the guessing rate threshold THS" means that the guessing rate is between 50 percent and 70 percent (i.e., the gap between the guessing rate and the guessing rate threshold THS does not exceed the tolerance value ε).

[0117] In particular, two successive visual acuity tests performed during the preliminary phase PP and / or the monitoring phase MP are spaced apart in time to be able to observe the effective evolution of the visual acuity value of the user 1. Preferably, the successive visual acuity tests follow a time period of one day, several days or weeks.

[0118] In step S4a, the visual acuity of user 1 is tested with a visual acuity reference value VA_ref. The digital device 2 is configured in a monitoring phase MP to display a series of (e.g., 10) visual targets with visual target reference size OS_ref, and the corresponding guessing rate X2.0 of user 1 is measured in response to the display of such series of visual targets. In particular, step S4a is separated in time from the preliminary phase PP so that the guessing rate X2.0 can potentially evolve from the guessing rate X1.x.

[0119] In step S4b, it is checked whether such guessing rate X2.0 remains approximately equal to the guessing rate threshold THS. In other words, in step S4b, it is checked whether the user 1 still obtains a guessing rate corresponding to the guessing rate threshold THS, which means that when the optotype is displayed with the optotype reference size OS_ref, the visual acuity reference value VA_ref remains the correct visual acuity value of the user 1 when step S4b is performed. Therefore, in step S4b, it is checked whether the gap between the guessing rate X2.0 and the guessing rate threshold THS still remains less than the tolerance value ε.

[0120] If the guess rate X2.0 corresponds to the guess rate threshold THS in step S4b, it means that the visual acuity of the user 1 in such step of the monitoring phase MP remains the same as the visual acuity of the user 1 during the preliminary phase PP (in other words, the previous visual acuity reference value VA_ref remains the correct visual acuity of the user 1). In such a case, after a certain period of time lasting, for example, several days or weeks, step S4a is repeated and the visual acuity reference value VA_ref is checked again to confirm the stability of the visual acuity of the user 1 or, conversely, to detect possible shifts in the visual acuity. If the guess rate X2.0 is not equal to the guess rate threshold THS in step S4b (in other words, the gap between the guess rate X2.0 and the guess rate threshold THS exceeds the tolerance value ε), it means that the visual acuity of the user 1 has progressed compared to the preliminary phase PP, and step S5 is then performed.

[0121] In step S5, by comparing the guess rate X2.0 with the guess rate threshold THS with the tolerance value ε, it is determined whether the visual acuity (and possibly the refractive error) of the user 1 has improved or deteriorated. If the guess rate X2.0 is inferior to the guess rate threshold THS (above the tolerance value ε), it can be understood that the myopia of the user 1 has worsened at that time and the visual acuity has deteriorated compared to the visual acuity reference value VA_ref of the user 1. In such a case, after a certain period of time lasting for example several days or weeks, a new step S51a of the monitoring phase MP is executed by taking into account a period without such visual acuity observation of the user 1. The visual acuity of the user 1 is tested with a new visual acuity level VA2.1, such new visual acuity level VA2.1 being inferior to the visual acuity reference value VA_ref. In other words, a series of optotypes with a new optotype size OS2.1 is displayed to the user 1 by the digital device 2, such new optotype size OS2.1 being larger than the optotype reference size OS_ref. The determination of the optotype size OS2.1 is based on the optotype size just tested (here the optotype reference size OS_ref) and a predefined monitoring function G such that OS2.1=G(OS_ref). Such a predefined monitoring function G may be a constant function whose essence consists in multiplying the optotype size value by a coefficient Ω, where Ω is strictly greater than 1. Then, in step S51b, a new guessing rate X2.1.1 is measured corresponding to the optotype size OS2.1 of the optotype displayed in step S51a. Then, the essence of the monitoring consists in comparing such guessing rate X21.1 with the guessing rate threshold THS in steps S51b and S61 in order to determine the visual acuity level to be tested in the next step (e.g., after a certain period of time has passed, a new visual acuity test is performed), similar to step S5. In step S51b, if the guessing rate X2.1.1 corresponds to the guessing rate threshold THS, it means that the optotype size OS2.1 is considered to be the optotype size reflecting the correct visual acuity level of the user 1 at the time of the test. The essence of the next step of the monitoring phase MP is to test such target size OS2.1 to determine whether the user's visual acuity has stabilized or progressed to visual acuity VA2.1.If the guess rate X2.1.1 does not correspond to the guess rate threshold THS in step S51b, it means that the tested visual acuity VA2.1 does not correspond to the exact visual acuity of the user 1 at the time of the test. If the guess rate X2.1.1 is inferior to the guess rate threshold THS by more than the tolerance value ε in step S61, such actual visual acuity is still inferior to the visual acuity VA2.1, and if the guess rate X2.1.1 is superior to the guess rate threshold THS by more than the tolerance value ε in step S61, such visual acuity is superior to the visual acuity VA2.1. The search for the actual visual acuity of the user 1 is continued by repeating the previous steps, replacing the guess rate X2.0 with the new guess rate S2.1.1 and replacing the optotype reference size OS_ref with the new optotype size OS2.1.

[0122] In step S5, if the guess rate X2.0 is better than the guess rate threshold THS (exceeding the tolerance value ε), it can be understood that the myopia of the user 1 has recovered during the test in step S4a and the visual acuity has improved compared to the visual acuity reference value VA_ref of the user 1. Such an improvement in the visual acuity of the user 1 may occur, for example, when the user undergoes a specific myopia treatment to correct the myopia. In such a case, after a certain period of time lasting, for example, several days or weeks, a new step S51a of the monitoring phase MP is executed by taking into account the observed improvement in the visual acuity of the user 1. The visual acuity of the user 1 is tested with a new visual acuity level VA2.2, and such a new visual acuity level VA2.2 is better than the visual acuity reference value VA_ref. In other words, a series of visual acuities with a new visual acuity size OS2.2 is displayed to the user 2 by the digital device 2, and such a new visual acuity size OS2.2 is smaller than the visual acuity reference size OS_ref. The determination of the target size OS2.2 is based on the last tested target size (here the target reference size OS_ref) and a predefined monitoring function G' such that OS2.1=G'(OS_ref). Such a predefined coefficient function G' may be a predefined constant function whose essence is to multiply the target size value by a coefficient Ω', where Ω' is strictly less than 1. In other words, since it is determined that the visual acuity has progressed positively, such positive progress is quantified by an increase in the tested visual acuity value (i.e. a decrease in the tested target size). Similar to steps S51b and S61, a new guess rate X2.1.2 corresponding to the target size 2.2 is measured, and the test steps S4b and S5 are repeated by replacing X2.0 with X2.1.2 and replacing VA_ref (and OS_ref) with VA2.2 (and OS2.2).

[0123] The predefined monitoring function G and the predetermined monitoring function G' are functions that are preset to change the test target size value when the visual acuity value of the user 1 decreases and improves, respectively. During the monitoring phase MP, in each iteration of the method of FIG. 5, both functions G and G' can be used successively to determine the next test target size to be tested. Depending on such functions G and G', the rate of increase or decrease of the test target size can be adapted during the monitoring phase MP. Equivalently, during the monitoring phase MP, the monitoring functions can be applied to the visual acuity value instead of the visual acuity value to test different visual acuity values.

[0124] Such steps of a monitoring phase MP can be repeated over time in order to measure the progression of myopia of the user 1. Such a monitoring phase MP can be terminated based on one or a combination of the following conditions: - the maximum number of repetitions of the visual acuity test is reached. This condition may be valid if the monitoring is performed, for example, during a predefined time between two appointments of the user 1 with an eye specialist. Based on the visual acuity reference value VA_ref determined at the first appointment, the user 1 may be able to periodically obtain data related to the evolution of his / her myopia until the next appointment with the eye specialist. - the guessing rate threshold THS reaches a predefined number of consecutive iterations of the search. This condition sets a criterion for defining the stability of the visual acuity of user 1. For example, in step S4b, if the guessing rate is equal to the guessing rate threshold THS over several consecutive display optotypes (e.g., three, which means that step 4a is repeated three times in succession) at the optotype reference size OS_ref, it is considered that the visual acuity of user 1 corresponds accurately and persistently to the visual acuity reference value VA_ref, and the visual acuity of user 1 is stable at the visual acuity level VA_ref. Therefore, the monitoring phase MP can be adapted since the tested visual acuity of user 1 is considered to be a priori accurate in the long term. The essence of such an adaptation can, for example, consist in extending the time interval between two consecutive visual acuity tests.

[0125] Now, reference is made to FIG. 6. FIG. 6 represents the time evolution of the guessing rate measured in response to a series of displayed targets for myopia monitoring of user 1. FIG. 6 details the data acquired by the digital device 2 when implementing the proposed method, including the preliminary phase pp and the monitoring phase MP. During the successive visual acuity tests, a series of targets with different target sizes is displayed to user 1, while the guessing rate of user 1 is measured for each displayed target in the series. The correct visual acuity of user 1 is considered to have been found when user 1 is able to correctly identify the displayed targets with a guessing rate corresponding to a guessing rate threshold THS preset to 0.60 (or 60 percent) when the tolerance ε is preset to 10 percent. In other words, the guessing rate included between the two dotted lines represented in FIG. 6 (corresponding to a guessing rate included between 50 percent and 70 percent) is considered to correspond to the guessing rate threshold THS, and the visual acuity being tested (in other words the visual acuity being tested) is considered to be the correct visual acuity of user 1 (in other words the correct visual acuity).

[0126] Any two consecutive vision tests are considered in Fig. 6 to be one week apart and are performed under similar test conditions. The positioning of the user relative to the mirror 3, the lighting conditions, the time of day, and e.g. the eye being tested in the case of a single vision test, remain the same for each vision test. In other embodiments, the interval between each vision test may be more or less than one week. The interval between vision tests performed during the preliminary phase PP and the monitoring phase MP may be of different lengths.

[0127] The essence of the myopia monitoring process depicted in FIG. 6 lies in a preliminary phase PP from week 0 to week 4 and a monitoring phase MP from week 5 to week 20.

[0128] During the preliminary phase PP, a visual acuity test is performed each week to determine the visual acuity reference value VA_ref of user 1. The steps of such a preliminary phase PP are detailed in Figures 3 and 4, and the guess rate in Figure 6 corresponds exactly to the results of the second user 1 (curve C2 in Figure 4). After the fourth week, the preliminary phase PP ends and a search algorithm is performed on the five measurements of the guess rate to determine the visual acuity reference value VA_ref of user 1.

[0129] As detailed in the description of Figures 3 and 4, the second visual acuity value to be tested is considered as the accurate visual acuity value of user 1 during the preliminary phase PP. In another embodiment, the visual acuity reference value VA_ref is determined by an interpolation search for the measurements performed (especially if the guessing rate corresponding to the guessing rate threshold THS during the preliminary phase PP is not accurately measured and needs to be estimated).

[0130] Then, a monitoring phase MP is started in the fifth week, the essence of which is to carry out successive visual acuity tests in order to assess the possible evolution of the visual acuity of user 1 from his visual acuity reference value VA_ref. The stopping condition of the monitoring phase MP is considered to be met if, in the example of FIG. 6, each measured guessing rate of user 1 corresponds to the guessing rate threshold value THS for eight consecutive weeks (reflecting a two-month stability of the visual acuity of user 1). In the fifth week (i.e. one week after determining the visual acuity reference value VA_ref of user 1), a visual acuity test is carried out by displaying to user 1 a series of optotypes with optotype reference size OS_ref. In the example shown by FIG. 6, such a visual acuity test produces a guessing rate that corresponds to the exact value of the guessing rate threshold value THS. The visual acuity test is therefore repeated one week later in the sixth week, in which the same visual acuity level (here VA_ref) is tested. As shown in FIG. 5, from the fifth week to the eleventh week, the guessing rates produced in the successive visual acuity tests correspond exactly to the guessing rate threshold value THS. However, a visual acuity test at week 12 with the visual acuity reference value VA_ref still produces a guess rate of 0.40 (or 40 percent), which is below the guess rate threshold THS by more than the tolerance value ε. Thus, it is understood that after seven weeks of vision stabilization with the visual acuity reference value VA_ref (weeks 5 to 11), a decline in visual acuity of user 1 was observed at week 12.

[0131] Thus, in the 13th week, the visual acuity test is performed at a different visual acuity level VA* (in other words, at a different value of the target size OS*), such visual acuity level being inferior to the visual acuity reference value VA_ref of user 1. Such visual acuity level VA* can be obtained by applying a monitoring function to the visual acuity reference value VA_ref or the target reference value OS_ref (in such a case, a predefined monitoring function G may be applied to test the target size value OS*) to take into account the observed deterioration of visual acuity in the 12th week. Such a monitoring function may be a constant function strictly equal to a number less than 1, and therefore the visual acuity level VA* tested in the 13th week is inferior to the visual acuity reference value VA_ref. Thus, the essence of the visual acuity test in the 13th week is to display the target with a target size OS* larger than the target reference size OS_ref. Then, it is observed that the guessing rate generated in the 13th week corresponds to the guessing rate threshold value THS. Thus, the monitoring phase MP continues, and the next visual acuity test is performed at the visual acuity level VA* as long as the guessing rate generated corresponds to the guessing rate threshold value THS. At week 20, the guess rate is measured to correspond to the guess rate threshold THS for eight consecutive weeks (weeks 13 through 20). Thus, the monitoring process may conclude that the user's long-term accurate visual acuity value is VA*. The process may also continue beyond week 20, for example, by extending the interval between visual acuity tests to a period of, for example, more than one week. Such a process may continue, for example, until the next appointment with an eye professional.

[0132] Thus, the accurate measurement of the visual acuity of user 1 at week 20 is VA*. Thus, the myopia monitoring process allows the assessment that user 1 has experienced visual acuity decline from week 0 to week 20, and such decline is quantified (using the monitoring function used to obtain VA*, such decline is quantified by the ratio VA* / VA_ref) and time-segmented (occurred at weeks 11-12). In another embodiment, the visual acuity tests may be spaced apart for periods longer or shorter than one week, depending, for example, on the required time precision or the age of user 1 (children's visual development is usually greater and more rapid than adults, e.g., more frequent myopia monitoring is required in children).

[0133] Reference is now made to figure 8, which represents a system for storing, processing and accessing data resulting from the proposed method. The digital device 2 represented in figures 1, 7 and 8 may record data relating to the evolution of the visual acuity value of one or several users 1 through successive visual acuity tests. Each visual acuity test is characterized by data relating at least to: - Temporal information about the test, such as time of test, timestamp, repetition, date, day of the week, etc. - the visual acuity level tested and / or the test target size (or target detail size), and - User 1's generated guess rate, which is determined based on the input data received from User 1.

[0134] Such data may for example be temporarily stored in the memory unit MEM of the digital device 2 at each iteration of the vision test and associated with an identifier of the user 1. Such an identifier is uniquely related to the user 1 and may for example be a medical identifier (such as for example a social security number in the French healthcare system) or a user account number of a myopia monitoring application. Such an identifier may also be associated with the digital device 2, for example if each digital device 2 is used for monitoring the vision situation of a single user 1. Several digital devices 2 depicted in Fig. 8 may compute the monitoring process and store in each memory unit MEM data related to successive vision tests performed for each user 1.

[0135] Furthermore, each digital device 2 is connected to a communication network NW (including, for example, a wireless communication network), whereby the digital device 2 may transmit signals and data to a distant server SER of the network via a communication interface INT-S of the server SER. The server SER may, for example, be a cloud server. In particular, such a server SER may include a storage memory that centralizes data received from the digital devices 2 in a database DB of the storage memory. Such a database DB may thus store data related to the visual acuity test, the number of visual acuity tests, the visual acuity reference value VA_ref in correspondence with an identifier of each user 1. Such a correspondence may, for example, be performed by the processing circuits (PROC-S, MEM-S) of the server SER. The database DB may also store medical records of the user 1, for example, regarding potential eye treatments or appointments. Such a database DB may be updated in real time by the processing circuits (PROC-S, MEM-S) of the server SER based on data received from the digital device 2 after each visual acuity test and may be accessible to other individuals 4 via other terminals connected to the server SER via the communication network NW. As a result, the results of the monitoring process of user 1 may be communicated in real time to the medical platform, the eye professional, or the surroundings of user 1 (e.g., the parents or ophthalmologist of user 1, etc.). In particular, the results of the myopia monitoring performed between two appointments with an eye professional may be communicated in real time to the eye professional (e.g., in the case of an eye treatment observation) or may be accessed by the eye professional during the next appointment. Such results may then enable an easy and immediate medical interpretation or diagnosis of the refractive error (e.g., myopia) of each user 1.

[0136] In a particular embodiment, the data transmitted by the digital device 2 to the server SER is processed by the processing circuits (PROC-S, MEM-S) of the server SER before being stored in the database DB of the storage memory. For example, the server SER may stamp the date and time of the visual acuity test or record the number of repetitions of the visual acuity test based on the real-time data received from the digital device 2. The digital device 2 may also transmit the tested target size and / or the response of the user 1 in raw form at each visual acuity test directly to the server SER, which processes such data to estimate the tested visual acuity level and / or the generated guess rate of the user 1. In another embodiment, the storage memory may be included directly in the digital device 2, for example as a part of the memory unit MEM of the digital device 2. [Explanation of symbols]

[0137] Reference Key 1: Digital device users 2: Digital devices 20: Front camera of digital device 22a: Physical switch, plus button on digital devices 22b: Physical switches, minus buttons on digital devices 2': Virtual image of digital device reflected in mirror 21': Virtual image of the display target by reflection in a mirror 3: Mirror D: Predefined distance between the user and the mirror d: Distance between the front camera of the digital device and the virtual image ΔD: Maximum deviation from a predefined distance value THS: guess rate threshold ε: Tolerance VA_ref: Visual acuity reference value OS_ref: Optotype reference size OS2.1: Second target size OS2.2: Third target size PP: Preliminary Phase MP: Monitoring Phase X1.1, X1.x, X1.n: Estimated values ​​measured during the preliminary phase VA1.1, VA1.2, VA1.n: visual acuity values ​​tested during the exploratory phase f: a given coefficient function of visual acuity g: A predefined coefficient function of target size β: a predefined coefficient less than 1 X2.1.1, X2.1.2: The guess rate values ​​measured during the monitoring phase OS2.1, OS2.2, OS*: Object size values ​​inspected during the monitoring phase VA2.1, VA2.2, VA*: visual acuity values ​​tested during the monitoring phase G: A predefined monitoring function for target size Ω: A predefined constant value greater than 1 G': a given monitoring function of target size Ω': a given constant value less than 1 4: Terminal user INT: Man / machine interface for digital devices PROC: Processing unit of a digital device MEM: Memory unit of a digital device COM: Output communication unit of digital device DB: A database contained in the server's memory SER: Server (PROC-S, MEM-S): Server processing circuit INT-S: Server communication interface NW: Communication network

Claims

1. A method for monitoring the progress of a visual acuity value of a user (1) of a digital device (2), said digital device (2) comprising: - displaying the optotypes at the selected optotype size to allow the user (1) to make a guess; - measuring a guess rate corresponding to the proportion of signs correctly identified by said user (1); configured to: The method comprises: a) determining a visual acuity reference value (VA_ref), the visual acuity reference value (VA_ref) being determined based on at least a predefined guessing ratio threshold (THS) of the optotype displayed at an optotype reference size (OS_ref); b) testing the evolution of the visual acuity value, b1) displaying the optotype at a first optotype size corresponding to the optotype reference size (OS_ref); - measuring the guess rate of the displayed stimulus; if the measured guess rate falls below the guess rate threshold (THS) by more than a tolerance value (ε); b2.1) Re-measure the guess rate of the optotype displayed in a second optotype size (OS2.1) that is higher than the first optotype size. - examining said evolution of said visual acuity value by The method includes:

2. Further steps: If the measured guess value exceeds the guess rate threshold (THS) by more than a tolerance (ε), 2.2) re-measuring the guess rate for a displayed object at a third object size (OS2.2) that is smaller than the first object size.

3. Further steps: If the gap between the measured guess rate and the guess rate threshold (THS) is less than or equal to a tolerance (ε), 2. The method of claim 1, further comprising: b2.3) re-measuring guess rates for indicia displayed at the same indicia size as the first indicia size.

4. The method of any one of claims 1 to 3, wherein the guess rate is remeasured after a predefined time.

5. The method of claim 4 , wherein the predefined period of time is seven days or more.

6. The method of claim 3, taken in combination with claim 2, further comprising a step of: c) determining the progress of the visual acuity value of the user (1) by comparing the visual acuity reference value (VA_ref) with at least another visual acuity value, the other visual acuity value being determined by the digital device (2) and associated with an optotype size that is the same as the first optotype size, the second optotype size (OS2.1), or the third optotype size (OS2.2) depending on the measured guess rate.

7. Further steps:

7. The method according to claim 6, further comprising the step of: d) monitoring the evolution of data relating to at least one refractive error of said user (1) based on said evolution of said visual acuity value of said user (1).

8. The method of any one of claims 1 to 7, wherein the guess rate threshold (THS) is between 50 percent and 70 percent.

9. The method according to any one of claims 1 to 8, wherein the tolerance (ε) is between 5 percent and 15 percent.

10. 4. The method of claim 3 taken in conjunction with claim 2, wherein steps b2.1), b2.2) and b2.3) are repeated through multiple iterations, and the first target size is replaced in each new iteration with a target size that is the same as either the first target size, the second target size (OS2.1), or the third target size (OS2.2), depending on the guess rate measured in a previous iteration.

11. The iterations are performed under the following conditions: - a preset maximum number of iterations is met; and - the first target size is replaced with the same target size for a predefined number of consecutive iterations; The method of claim 10 , further comprising terminating when at least one or a combination of the following is satisfied:

12. The visual acuity reference value (VA_ref) is - displaying a plurality of successive targets with a plurality of successive corresponding target sizes; - measuring a corresponding guess rate for each corresponding indicium size of the displayed indicium among the plurality of displayed indicium, where at least one guess rate (X1.1) is above the guess rate threshold (THS) and at least one other guess rate (X1.n) is below the guess rate threshold (THS); - identifying a displayed optotype, the corresponding guess rate (X1.x) corresponds to the guess rate threshold (THS), the corresponding optotype size corresponds to the optotype reference size (OS_ref), and the visual acuity reference value (VA_ref) is related to the corresponding optotype size; The method according to any one of claims 1 to 11, wherein the determination is made by carrying out

13. 13. The method of claim 12, wherein the displaying of the plurality of successive indicia and measuring the respective corresponding guessing rates follows a predetermined period, the period being one day or more.

14. 14. The method according to claim 12 or 13, wherein any two consecutive corresponding indicium sizes have different values, the ratio of such values ​​corresponding to a coefficient determined by a predetermined coefficient function (G).

15. The method according to any one of claims 12 to 14, wherein the visual acuity reference value (VA_ref) is determined by performing an interpolation search on the plurality of consecutive optotypes displayed at the plurality of consecutive corresponding optotype sizes and the corresponding guess ratios.

16. The digital device (2) is positioned by the user (1) such that the displayed visual indicia is reflected in a mirror (3) facing the user (1); The method further comprises, before measuring and / or re-measuring the guess rate of the displayed indicia: collecting ambient data relating to a current usage of the digital device (2), such ambient data including: the distance (d) between the position of the digital device (2) and the virtual image (2') of the digital device (2) created on the mirror (3) by the reflection of the digital device (2), - the level of ambient light, and - a time stamp associated with the displayed stimulus; and The method according to any one of claims 1 to 15, wherein the displayed visual indicia depends on the collected ambient data.

17. At a first time, the visual acuity reference value (VA_ref) and the optotype reference size (OS_ref) are determined; At a second time, a visual object displayed at the first visual object size and the measured guessing rate are determined; At a third time, the indicia displayed at the second indicia size (OS2.1) and the re-measured guessing rate are determined; At least one storage memory is provided; - data relating to said visual acuity reference value (VA_ref) and / or said optotype reference size (OS_ref) are stored in said storage memory corresponding to said first time data, - data relating to the first indicium size and the measured guess rate are stored in the storage memory in correspondence with the data at the second time; - data relating to the second target size (OS2.1) and the re-measured guessing rate are stored in the storage memory in correspondence with the data at the third time; The method according to any one of the preceding claims, wherein said data is further stored corresponding to an identifier of said user (1).

18. The method according to claim 17, wherein the storage memory stores data in a database (DB) accessible by at least one terminal through a communication network (NW), thereby providing at least a history of the progress of the visual acuity value to a user (4) of the terminal.

19. A digital device (2) comprising a communication interface (COM) with at least one screen, a man / machine interface (INT) and a processing circuit configured to implement the method according to any one of claims 1 to 18.

20. The output data of the digital device (2) is, for a given user (1): - visual acuity reference value (VA_ref), - the selected target size of the displayed target, and - The guess rate of the displayed stimulus Including, The digital device (2) according to claim 19, wherein the digital device (2) is connected to a communication network (NW) and configured to transmit the output data via the communication network (NW) to a remote server (SER).

21. A server (SER), connected to a communication network (NW) and having a storage memory for storing a database (DB) for implementing the method of claim 18, said database (DB) being accessible by at least one terminal and providing at least a history of the progress of visual acuity values ​​to a user (4) of said terminal.

22. A computer program product comprising program instruction codes stored on a computer readable medium for carrying out the method of any one of claims 1 to 18.

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