Patent Publication Number: US-2021186323-A1

Title: Vision quality assessment based on machine learning model and wavefront analysis

Description:
INTRODUCTION 
     The disclosure relates generally to a system and method of assessing vision quality of an eye, based on at least one machine learning model and wavefront analysis. Humans have five basic senses: sight, hearing, smell, taste and touch. Sight gives us the ability to visualize the world around us and connects us to our surroundings. According to some scientific reports, the brain devotes more space to processing and storing visual information than the other four senses combined, underscoring the importance of sight. Many people worldwide have issues with quality of vision, due in large part to refractive errors. Refractive errors of the eye may be generally categorized as lower-order aberrations and higher-order aberrations. Lower-order aberrations include nearsightedness, farsightedness as well as astigmatism. Higher-order aberrations include many varieties of aberrations, such as coma, trefoil and spherical aberration. Traditional eye examination procedures result in an assessment of vision quality that only assess the lower-order aberrations of the eye. 
     SUMMARY 
     Disclosed herein is a system and method of assessing vision quality of an eye, with a controller having a processor and tangible, non-transitory memory on which instructions are recorded. The controller is configured to selectively execute at least one machine learning model. Execution of the instructions by the processor causes the controller to: receive wavefront aberration data of the eye and express the wavefront aberration data as a collection of Zernike polynomials. The controller is configured to obtain a plurality of input factors based on the collection of Zernike polynomials. The plurality of input factors is fed into at least one machine learning model, which is trained to analyze the plurality of input factors. The machine learning model generates at least one vision correction factor based in part on the plurality of input factors. The vision correction factor may be programmed into a laser device for reshaping the eye during a vision correction procedure/refractive surgery. The vision correction factor may be employed for aiding in the selection of spectacles, contact lens and/or intraocular lens for the eye. 
     The plurality of input factors may include respective wavefront coefficients for defocus, primary spherical aberration, oblique astigmatism and vertical astigmatism. The vision correction factor may be a manifest refraction spherical equivalent. The vision correction factor may be a log MAR (logarithm of a minimum angle of resolution) uncorrected visual acuity factor. The at least one machine learning model may incorporate a neural network and/or a support vector regression model. 
     The machine learning model may include a first machine learning model and a second machine learning model. Training the first machine learning model may include receiving a first training dataset having respective wavefront aberration measurements and respective measured manifest refraction spherical equivalent values of a first set of patients. First training input values are obtained based upon the respective wavefront aberration measurements and applied to a respective input layer of the first machine learning model. The respective measured manifest refraction spherical equivalent values may include pre-operative data and post-operative data. The respective measured manifest refraction spherical equivalent values may be fed to a respective output layer of the first machine learning model. 
     The first training input values may be employed to generate a first plurality of weight values associated with respective nodes of the first machine learning model. The first set of patients in the first training dataset may be characterized by a respective health status and/or a respective biometric parameter fitting within a first predefined maximum and a first predefined minimum. The respective biometric parameter may be an anterior chamber depth, a lens thickness, lens diameter or other dimension. 
     Training the second machine learning model may include receiving a second training dataset having the respective wavefront aberration measurements and the respective measured manifest refraction spherical equivalent values of a second set of patients. Second training input values are obtained based upon the respective wavefront aberration measurements. The second training input values are applied to the respective input layer of the second machine learning model. The respective measured manifest refraction spherical equivalent values are fed to the respective output layer of the second machine learning model. The second training input values may be used to generate a second plurality of weight values associated with respective nodes of the second machine learning model. The second set of patients in the second training dataset may be characterized by a respective health status and/or respective biometric parameter fitting within a second predefined maximum and a second predefined minimum. 
     The above features and advantages and other features and advantages of the present disclosure are readily apparent from the following detailed description of the best modes for carrying out the disclosure when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a system for assessing vision quality of an eye, the system having a controller; 
         FIG. 2  is a schematic flowchart for a method executable by the controller of  FIG. 1 ; 
         FIG. 3  is a schematic example of a neural network executable by the controller of  FIG. 1 ; 
         FIG. 4  is a schematic example of a support vector regression (SVR) network executable by the controller of  FIG. 1 ; 
         FIG. 5  is a schematic graph illustrating measured values (vertical axis) and predicted values (horizontal axis) of the manifest refraction spherical equivalent for pre-operative data; 
         FIG. 6  is a schematic graph illustrating measured values (vertical axis) and predicted values (horizontal axis) of the manifest refraction spherical equivalent for post-operative data; and 
         FIG. 7  is a schematic graph illustrating measured values (vertical axis) and predicted values (horizontal axis) of log MAR (logarithm of a minimum angle of resolution) uncorrected visual acuity for pre-operative and post-operative data. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  schematically illustrates a system  10  for assessing vision quality of an eye E. As described below, the system  10  employs a robust approach utilizing one or more machine learning models, optimizing the assessment of vision quality and resulting in a greater success rate for prediction of vision quality. Referring to  FIG. 1 , the system  10  includes a refraction device  12  having a light source  14  configured to project a beam  16  of light into the eye E. The beam  16  is reflected by the retina R. Referring to  FIG. 1 , the reflected light  20  exits the eye E as wavefront  24 , after travelling through the lens  22 . The wavefront  24  is characterized by distortions unique to the physical construction of the eye E. 
     Referring to  FIG. 1 , the wavefront  24  is captured by a lenslet array  26  and detected by a sensor  30 . An aberration map of the eye E is created by comparing the shape of the wavefront  24  captured with that of a pre-programmed reference wavefront having the same pupil size (as the wavefront  24  passes through the pupil in the eye E). For example, points of difference between the two may be obtained at specific points. The refraction device  12  may include associated beam guiding elements (not shown), electronic components and other components available to those skilled in the art. It is understood that the refraction device  12  may take many different forms and include multiple and/or alternate components. 
     Referring to  FIG. 1 , the system  10  includes a controller C configured to receive data from the sensor  30 . The controller C may be embedded in the refraction device  12 . Referring to  FIG. 1 , the controller C may be configured to communicate with the refraction device  12  and other entities via a short-range network  32 . The short-range network  32  may be wireless or may include physical components. The short-range network  32  may be a bus implemented in various ways, such as for example, a serial communication bus in the form of a local area network. The local area network may include, but is not limited to a Controller Area Network (CAN), a Controller Area Network with Flexible Data Rate (CAN-FD), Ethernet, blue tooth, WIFI and other forms of data connection. The short-range network  32  may be a Bluetooth™ connection, defined as being a short-range radio technology (or wireless technology) aimed at simplifying communications among Internet devices and between devices and the Internet. Bluetooth™ is an open wireless technology standard for transmitting fixed and mobile electronic device data over short distances and creates personal networks operating within the 2.4 GHz band. Other types of connections may be employed. 
     Referring to  FIG. 1 , the controller C may be in communication with a user interface  34 , which may include a display unit. Additionally, the controller C may be configured to communicate with a remote server  40  and/or a cloud unit  42 , via a long-range network  44 . The remote server  40  may be a private or public source of information maintained by an organization, such as for example, a research institute, a company, a university and/or a hospital. The cloud unit  42  may include one or more servers hosted on the Internet to store, manage, and process data. The long-range network  44  may be a Wireless Local Area Network (LAN) which links multiple devices using a wireless distribution method, a Wireless Metropolitan Area Networks (MAN) which connects several wireless LANs or a Wireless Wide Area Network (WAN) which covers large areas such as neighboring towns and cities. Other types of connections may be employed. 
     The controller C may be configured to receive and transmit wireless communication to the remote server  40  through a mobile application  46 , shown in  FIG. 1 . The mobile application  46  may in communication with the controller C via the short-range network  32  such that it has access to the data in the controller C. In one example, the mobile application  46  is physically connected (e.g. wired) to the controller C. In another example, the mobile application  46  is embedded in the controller C. The circuitry and components of a remote server  40  and mobile application  46  (“apps”) available to those skilled in the art may be employed. 
     The controller C has at least one processor P and at least one memory M (or non-transitory, tangible computer readable storage medium) on which are recorded instructions for executing a method  100 . Method  100  is shown in and described below with reference to  FIG. 2 . The controller C is specifically programmed to selectively execute one or more machine learning models  35  (“one or more” omitted henceforth), such as first machine learning model  36  and second machine learning  38 , shown in  FIG. 1 . The controller C may access the machine learning models  35  via the short-range network  32 , the long-range network  44  and/or mobile application  46 . Alternatively, the machine learning models  35  may be embedded in the controller C. The machine learning models  35  may be configured to find parameters, weights or a structure that minimizes a respective cost function and may incorporate respective regression models. 
     Referring now to  FIG. 2 , a flow chart of method  100  executable by the controller C of  FIG. 1  is shown. Method  100  need not be applied in the specific order recited herein and some blocks may be omitted. The memory M can store controller-executable instruction sets, and the processor P can execute the controller-executable instruction sets stored in the memory M. 
     Per block  110  of  FIG. 2 , the controller C is configured to receive wave front aberration data of the eye E and translate or express it in terms of a collection of Zernike polynomials. The wavefront aberration data (A) is decomposed into a set of orthogonal polynomials on a circle such that: A=Σ i,j a i,j Z i   j , where a i,j  are respective wavefront coefficients measured on the eye E and Z i   j  represents a Zernike polynomial. Each Zernike polynomial describes the type or kind of aberration existing at a specific point on the wavefront  24  after it passes through the eye E. 
     The controller C is configured to obtain a plurality of input factors based on the collection of Zernike polynomials, with the plurality of input factors being one or more of the respective wavefront coefficients measured on the eye E. In one example, the controller C employs two input factors: the respective wavefront coefficients for defocus (Z 2   0 ) and primary spherical aberration (Z 4   0 ). In another example, the controller C employs four input factors: respective wavefront coefficients for defocus (Z 2   0 ), primary spherical aberration (Z 4   0 ), oblique astigmatism (Z 2   −2 ) and vertical astigmatism (Z 2   2 ). 
     Per block  120  of  FIG. 2 , the method  100  includes feeding the plurality of input factors into the machine learning models  35 , which are trained to analyze the plurality of input factors. Per block  130  of  FIG. 2 , the controller C is configured to generate at least one vision correction factor by executing the machine learning models  35 , based in part on the plurality of input factors. The vision correction factor may include components of refraction: sphere, cylinder and spherical equivalent, and may be expressed as a manifest refraction spherical equivalent (MRSE). The vision correction factor may be expressed as a log MAR (logarithm of a minimum angle of resolution) uncorrected visual acuity factor. The vision correction factor may be employed to establish ablation profiles for refractive surgery, as well as for aiding in the selection of spectacles, contact lens and/or intraocular lens for the eye. Additionally, the controller C may be configured to create a patient profile for the patient (with the eye E) in the cloud  42  and/or remote server  40 , via the long-range network  44 , and upload or “save” the vision correction factor into the patient profile. 
     The machine learning models  35  of  FIG. 1  may include a neural network, an example of which is shown in  FIG. 3 . Referring to  FIG. 3 , the neural network  200  is a feedforward artificial neural network having at least three layers, including an input layer  201 , at least one hidden layer  220  and an output layer  240 . Each layer is composed of respective nodes N configured to perform an affine transformation of a linear sum of inputs. The respective nodes N are characterized by a respective bias and respective weighted links. The parameters of each respective node N may be independent of others, i.e., characterized by a unique set of weights. The input layer  201  may include first input node  202 , second input node  204 , third input node  206 , fourth input node  208 , fifth input node  210  and sixth input node  212 . The respective nodes N in the input layer  201  receive the input, normalize them and forward them to respective nodes N in the hidden layer  220 . 
     Referring to  FIG. 3 , the hidden layer  220  may include first hidden node  222 , second hidden node  224 , third hidden node  226 , fourth hidden node  228  and fifth hidden node  230 . Each respective node N in a subsequent layer computes a linear combination of the outputs of the previous layer. A network with three layers would form an activation function ƒ(x)=ƒ(3)(ƒ(2)(ƒ(1)(x))). The activation function ƒ may be linear for the respective nodes N in the output layer  240 . The activation function ƒ may be a sigmoid for the hidden layer  220 . A linear combination of sigmoids may be used to approximate a continuous function characterizing the output vector y. The patterns recognized by the neural network  200  may be translated or converted into numerical form and embedded in vectors or matrices. 
     The machine learning models  35  may include a support vector regression model  300 , an example of which is shown in  FIG. 4 . The support vector regression model  300  is configured to find a function (hyperplane  304  in  FIG. 4 ) such that the data points  302  are within a margin  306  from this function, i.e., inside a first boundary line  308  and a second boundary line  310 . Referring to  FIG. 4 , the hyperplane  304  may be defined as the line that will match the input vector x to the output vector y, i.e. predict a target value. The hyperplane  304  is individualized so as to maximize the margin  306  and minimize a predefined error. If there are points (such as extraneous point  312 ) that are outside the margin  306 , a penalty may be built into the support vector regression model  300 . Prior to ascertaining the hyperplane  304 , the support vector regression model  300  may employ a kernel function to map a lower dimensional dataset into a higher dimensional dataset. Other machine learning models available to those skilled in the art may be employed. 
     The machine learning models  35  may employ deep learning maps to match an input vector x to an output vector y by learning an activation function ƒ such that ƒ(x) maps toy. A training process enables the machine learning models  35  to correlate the appropriate activation function ƒ(x) for transforming the input vector x to the output vector y. For example, in the case of a simple linear regression model, two parameters are learned: a bias and a slope. The bias is the level of the output vector y when the input vector x is 0 and the slope is the rate of predicted increase or decrease in the output vector y for each unit increase in the input vector x. Once the machine learning models  35  are respectively trained, estimated values of the output vector y may be computed with new values of the input vector x. 
     Referring to  FIG. 1 , the controller C may be configured to obtain one or more training datasets from the remote server  40  via the long-range network  44 . Training the first machine learning model  36  and second machine learning model  38  may include receiving a first training dataset and a second training dataset having respective wavefront aberration measurements and respective measured manifest refraction spherical equivalent values of a first set of patients and a second set of patients, respectively. The training datasets may be stratified based on biometric parameters of the eye. In other words, the process may be optimized by grouping the training datasets for similar-sized dimensions of eyes or other health status factors (e.g. grouping patients affected by glaucoma in the first set of patients and patients affected by a history of retinal detachment in the second set of patients). 
     In one non-limiting example, the first set of patients in the first training dataset may be characterized by a respective biometric parameter fitting within a first predefined maximum and a first predefined minimum. The respective biometric parameter may be an anterior chamber depth, a lens thickness, lens diameter or other physical dimension of the eye. The second set of patients in the second training dataset may be characterized by a respective biometric parameter fitting within a second predefined maximum and a second predefined minimum. 
     First and second training input values may be respectively obtained based upon the respective wavefront aberration measurements and applied to a respective input layer of the first machine learning model  36  and second machine learning model  38 . The respective measured manifest refraction spherical equivalent values may include pre-operative data and post-operative data. The respective measured manifest refraction spherical equivalent values may be fed to a respective output layer of the first machine learning model  36  and second machine learning model  38 . The first and second training input values, respectively, may be used to generate a first plurality of weight values and a second plurality of weight values associated with respective nodes of the first machine learning model  36  and second machine learning model  38 . This may be done by a training program separate from the refraction device  12  and/or controller C. 
     Referring now to  FIGS. 5, 6 and 7 , schematic graphs are shown representing various examples of fitted models using a topographic guided laser refractive study.  FIG. 5  shows model fit line  400  for pre-operative data, with the vertical axis Y1 indicating measured manifest refraction spherical equivalent (MRSE) values, and the horizontal axis X1 indicating predicted MRSE values.  FIG. 6  shows model fit line  500  for post-operative data, with the vertical axis Y2 indicating measured MRSE values, and the horizontal axis X2 indicating predicted MRSE values. Note that the scales are different in  FIGS. 5 and 6 , with  FIG. 6  having a smaller respective range. 
       FIG. 7  shows model fit line  600  and respective contours  610  for both preoperative and post-operative data, with the vertical axis Y3 indicating measured log MAR (logarithm of a minimum angle of resolution) uncorrected visual acuity values, and the horizontal axis X3 indicating predicted log MAR (logarithm of a minimum angle of resolution) uncorrected visual acuity values. Table 1 and Table 2 below show a comparison of the fitted models of  FIGS. 5 and 6 , respectively, with a linear sum of second order Zernike polynomials and fourth order Zernike polynomials. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Pre-Operative Data 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Machine  
                   
                   
               
               
                   
                   
                 Learning 
                 2 nd  Order  
                 4 th  Order  
               
               
                   
                   
                 Model Fit 
                 Zernike 
                 Zernike 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Mean Absolute 
                 0.314 
                 0.437 
                 0.531 
               
               
                   
                 Prediction Error 
                   
                   
                   
               
               
                   
                 Percentage Success 
                 78.0 
                 65.5 
                 54.1 
               
               
                   
                 Deviation Factor 
                 0.988 
                 0.987 
                 0.984 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Post-Operative Data 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Machine  
                   
                   
               
               
                   
                   
                 Learning 
                 2 nd  Order  
                 4 th  Order  
               
               
                   
                   
                 Model Fit 
                 Zernike 
                 Zernike 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Mean Absolute 
                 0.194 
                 0.378 
                 0.423 
               
               
                   
                 Prediction Error 
                   
                   
                   
               
               
                   
                 Percentage Success 
                 93.1 
                 73.4 
                 68.9 
               
               
                   
                 Deviation Factor 
                 0.090 
                 0.193 
                 0.167 
               
               
                   
                   
               
            
           
         
       
     
     As shown by Table 1 and Table 2 above, the machine learning models  35  improve both the mean absolute prediction error and the prediction success rate for assessment of vision quality. Additionally, the system  10  eliminates the need for pupil diameter rescaling when observing objects at distance. 
     The controller C of  FIG. 1  includes a computer-readable medium (also referred to as a processor-readable medium), including a non-transitory (e.g., tangible) medium that participates in providing data (e.g., instructions) that may be read by a computer (e.g., by a processor of a computer). Such a medium may take many forms, including, but not limited to, non-volatile media and volatile media. Non-volatile media may include, for example, optical or magnetic disks and other persistent memory. Volatile media may include, for example, dynamic random-access memory (DRAM), which may constitute a main memory. Such instructions may be transmitted by one or more transmission media, including coaxial cables, copper wire and fiber optics, including the wires that comprise a system bus coupled to a processor of a computer. Some forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, other magnetic medium, a CD-ROM, DVD, other optical medium, punch cards, paper tape, other physical medium with patterns of holes, a RAM, a PROM, an EPROM, a FLASH-EEPROM, other memory chip or cartridge, or other medium from which a computer can read. 
     Look-up tables, databases, data repositories or other data stores described herein may include various kinds of mechanisms for storing, accessing, and retrieving various kinds of data, including a hierarchical database, a set of files in a file system, an application database in a proprietary format, a relational database management system (RDBMS), etc. Each such data store may be included within a computing device employing a computer operating system such as one of those mentioned above, and may be accessed via a network in one or more of a variety of manners. A file system may be accessible from a computer operating system, and may include files stored in various formats. An RDBMS may employ the Structured Query Language (SQL) in addition to a language for creating, storing, editing, and executing stored procedures, such as the PL/SQL language mentioned above. 
     The detailed description and the drawings or FIGS. are supportive and descriptive of the disclosure, but the scope of the disclosure is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed disclosure have been described in detail, various alternative designs and embodiments exist for practicing the disclosure defined in the appended claims. Furthermore, the embodiments shown in the drawings or the characteristics of various embodiments mentioned in the present description are not necessarily to be understood as embodiments independent of each other. Rather, it is possible that each of the characteristics described in one of the examples of an embodiment can be combined with one or a plurality of other desired characteristics from other embodiments, resulting in other embodiments not described in words or by reference to the drawings. Accordingly, such other embodiments fall within the framework of the scope of the appended claims.