US-12622582-B2 - Method and device for determining a refraction feature of an eye of a subject using an image-capture device

US12622582B2US 12622582 B2US12622582 B2US 12622582B2US-12622582-B2

Abstract

A system and method for determining a refraction feature of an eye of a subject using an image-capture device, the method including acquiring at least one picture of the retina of the eye of the subject, and determining the refraction feature based on a blur level of the acquired picture of the retina.

Inventors

Stephane Boutinon

Assignees

ESSILOR INTERNATIONAL

Dates

Publication Date: 20260512
Application Date: 20200611
Priority Date: 20190613

Claims (14)

1 . A method for determining a refraction feature of an eye of a subject using an image-capture device, said method comprising: acquiring at least one picture of a retina of the eye of the subject; and determining said refraction feature based on a blur level of said acquired picture of the retina, the blur level of a picture being determined using a value of a point spread function associated with said acquired picture, said refraction feature being determined by: calculating a modified picture having a reduced blur level compared to an initial blur level of said acquired picture of the retina, said value of a point spread function associated with said acquired picture is derived from the acquired picture and the modified picture using a deconvolution method, and identifying one theoretical value of a point spread function of a plurality of theoretical values of the point spread function which has a minimal difference between said value of the point spread function associated with said acquired picture and the one theoretical value of the point spread function of the plurality of theoretical values of the point spread function, to determine the corresponding theoretical value of the point spread function and the refraction feature associated with the corresponding theoretical value of the point spread function and thus the refraction feature of the eye of the subject, or optimizing the value of the point spread function associated with said acquired picture among the plurality of theoretical values of the point spread function to determine the corresponding theoretical value of the point spread function and the refraction feature associated with the corresponding theoretical value of the point spread function and thus the refraction feature of the eye of the subject, an optimal value of the point spread function being determined considering the modified picture with a different contrast level compared to an initial contrast level of the acquired picture, each theoretical value of the point spread function of the plurality of theoretical values of the point spread function being determined theoretically from an arbitrary refraction feature which is thus associated with said theoretical value of the point spread function, said arbitrary refraction feature being used to determine Zernike coefficients and derive an expression of a wavefront to calculate said theoretical value of the point spread function of the plurality of theoretical values of the point spread function, the plurality of theoretical values of the point spread function being determined before an execution of the method for determining a refraction feature.
2 . The method according to claim 1 , wherein said refraction feature is determined by using a model relating said blur level of the acquired picture of the retina to the refraction feature.
3 . The method according to claim 1 , further comprising acquiring at least a picture of a pupil of the eye of the subject, the determining said refraction feature depending on a pupil diameter determined from said picture of the pupil.
4 . The method according to claim 3 , further acquiring another picture of the retina of the eye of the subject, said another picture is acquired at another focus distance comprised between the one of said acquired picture of the retina and the one of said picture of the pupil of the eye, said refraction feature also depending on said another picture of the retina, said another acquired picture being suitable for determining a sign of the refraction feature, the sign of the refraction feature being determined comparing the blur level between said another acquired picture of the retina and said acquired picture of the retina.
5 . The method according to claim 1 , wherein the blur level is determined using a convolutional neural network.
6 . The method according to claim 5 , wherein the convolutional neural network is trained using a dataset of couples of images, each couple of images being associated with a specific refraction feature.
7 . The method according to claim 6 , further comprising determining a value of a point spread function associated with the acquired picture of the retina by using the training of the convolutional neural network with the dataset of couples of images.
8 . The method according to claim 6 , further comprising determining the refraction feature associated with the acquired picture of the retina by using the training of the convolutional neural network with the dataset of couples of images.
9 . The method according to claim 1 , wherein the modified picture is calculated using a blind deconvolution method of the acquired picture of the retina.
10 . The method according to claim 9 , wherein the blind deconvolution method is based on a dataset of values of the point spread function, each value of the point spread function being associated with a specific refraction feature.
11 . The method according to claim 10 , wherein the modified picture is determined selecting an optimal value of the point spread function among said dataset of values of the point spread function, the optimal value of the point spread function corresponding to an improved contrast level in the modified picture compared to an initial contrast level of the acquired picture of the retina.
12 . The method according to claim 1 , wherein the picture of the retina is acquired with an image capture device with a focus distance at infinity.
13 . The method according to claim 1 , wherein a distance between the eye of the subject and the image-capture device is higher than 20 mm.
14 . A system for determining a refraction feature of an eye of a subject comprising: an image-capture device suitable for acquiring at least one picture of a retina of the eye of the subject; and a data processor suitable for determining said refraction feature based on a blur level of said acquired picture of the retina, a blur level of a picture being determined using a value of a point spread function associated with said acquired picture, said data processor being suitable for determining the refraction feature by: calculating a modified picture having a reduced blur level compared to an initial blur level of said acquired picture of the retina, said value of a point spread function associated with said acquired picture being derived from the acquired picture and the modified picture using a deconvolution method, and identifying one theoretical value of a point spread function of a plurality of theoretical values of the point spread function which has a minimal difference between said value of the point spread function associated with said acquired picture and the one theoretical value of the point spread function of the plurality of theoretical values of the point spread functions, to determine the corresponding theoretical value of the point spread function and the refraction feature associated with the corresponding theoretical value of the point spread function and thus the refraction feature of the eye of the subject, or optimizing the value of the point spread function associated with said acquired picture among the plurality of theoretical values of the point spread function to determine the corresponding theoretical value of the point spread function and the refraction feature associated with the corresponding theoretical value of the point spread function and thus the refraction feature of the eye of the subject, an optimal value of the point spread function being determined considering the modified picture with a different contrast level compared to an initial contrast level of the acquired picture, said data processor being suitable for determining theoretically each theoretical value of the point spread function of the plurality of theoretical values of the point spread function from an arbitrary refraction feature which is thus associated with said theoretical value of the point spread function, said arbitrary refraction feature being used to determine Zernike coefficients and derive an expression of a wavefront to calculate said theoretical value of the point spread function of the plurality of theoretical values of the point spread function, the plurality of theoretical values of the point spread function being determined before an execution of determining a refraction feature.

Description

TECHNICAL FIELD OF THE INVENTION The invention relates to a method and a system for determining a refraction feature of an eye of a subject. BACKGROUND INFORMATION AND PRIOR ART Numerous documents describe devices and methods for determining such a refraction feature. In particular, methods of autorefraction are known for determining objective values of the refraction of a subject. These methods are complex and sometimes time-consuming. They usually imply the use of large and expensive devices that need a qualified person to be handled. In particular, they require the use of a specific instrument having a camera and multiple light sources placed in a same plane. The access to these methods of autorefraction is therefore limited and a large part of the world population does not benefit from them. SUMMARY OF THE INVENTION Therefore one object of the invention is to provide a new method for determining a refraction feature of an eye of a subject that would be simplified in that it would not require the use of specific material or the intervention of qualified people. More precisely, the invention consists in a method for determining a refraction feature of an eye of a subject using an image-capture device. The method comprises the following steps: acquiring at least one picture of the retina of the eye of the subject, and determining said refraction feature based on a blur level of said acquired picture of the retina, a blur level of a picture being determined using a value of a point spread function associated with said picture, said refraction feature being determined by calculating a modified picture having a reduced blur level compared to an initial blur level of said acquired picture of the retina. Such a method may be implemented by the subject himself, and carried on using only a smartphone, or a tablet computer, with no added optical components or an augmented reality display. It is therefore accessible to a wide range of population including some that are excluded from the access to existing methods. Other advantageous features of the method are the following ones: said refraction feature is determined by using a model relating said blur level of the acquired picture of the retina to the refraction feature;the method further comprises a step of acquiring at least a picture of a pupil of the eye of the subject, the step of determining said refraction feature depending on a pupil diameter determined from said picture of the pupil;the blur level is determined using a convolutional neural network;the neural network is trained using a dataset of couples of images, each couple of images being associated with a specific refraction feature;the method further comprises a step of determining a value of a point spread function associated with the acquired picture of the retina by using the training of the neural network with the dataset of couples of images;the method further comprises a step of determining the refraction feature associated with the acquired picture of the retina by using the training of the neural network with the dataset of couples of images;the modified picture is calculated using a blind deconvolution method of the acquired picture of the retina;the blind deconvolution method is based on a dataset of values of the point spread function, each value of the point spread function being associated with a specific refraction feature;the modified picture is determined selecting an optimal value of the point spread function among said dataset of values of the point spread function, the optimal value of the point spread function corresponding to an improved contrast level in the modified picture compared to an initial contrast level of the acquired picture of the retina;the picture of the retina is acquired with a focus distance at infinity;the distance between the eye of the subject and the image-capture device is higher than 20 mm; andthe method further comprises a step of acquiring another picture of the retina of the eye of the subject, said another picture is acquired at another focus distance comprised between the one of said acquired picture of the retina and the one of said picture of the pupil of the eye, said refraction feature also depending on said another picture of the retina, said another acquired picture being suitable for determining a sign of the refraction feature, the sign of the refraction feature being determined comparing the blur level between said another acquired picture of the retina and said acquired picture of the retina. The invention also comprises a system for determining a refraction feature of an eye of a subject comprising: an image-capture device suitable for acquiring at least one picture of the retina of the eye of the subject, and a data processor suitable for determining said refraction feature based on a blur level of said acquired picture of the retina, a blur level of a picture being determined using a value of a point spread function associa