Apparatus and method for determining subjective responses using objective characterization of vision based on wavefront sensing

Abstract

An apparatus for determining the refraction of a patient's eye includes a wavefront measurement device that determines aberrations in a return beam from the patient's eye viewing a target through a corrective test lens in the apparatus. The wavefront measurement device preferably outputs an display representative of the quality of vision afforded the patient through the test lens. The display may be, e.g., a representation of a Snellen chart convolved with the optical characteristics of the patient's vision, an overall quality of vision scale, or the optical contrast function, all of which are based on the wavefront measurements of the patient's eye. The examiner may use the display information to conduct a refraction examination or other vision tests without the subjective response from the patient.

1 . An apparatus for determining the refraction of a patient's eye focused on a physical target, said apparatus comprising: 
 a light source;    optics directing light from said light source to the patient's eye, said light reflecting from a surface of said eye, said reflected light comprising a plurality of wavefronts;    a wavefront measurement device positioned along a first optical path to said eye to measure the shape of said wavefronts reflected from the patient's eye; and    at least one test lens disposable along a second optical path between the patient's eye and the physical target,    wherein said optics and said at least one test lens are arranged such that when said patient looks at said physical target through said test lens, said light from said light source is directed through said eye so as to determine said refraction from said wavefronts returning from said eye.    
     
     
         2 . The apparatus of  claim 1 , further comprising a beamsplitter for merging said first optical path from said wavefront sensor to said eye and said second optical path from said eye to said physical target such that they overlap in a region between said beam splitter and said eye.  
     
     
         3 . The apparatus of  claim 1 , wherein said test lens is disposed in said region between said patient's eye and said beamsplitter where said first and second optical paths overlap.  
     
     
         4 . The apparatus of  claim 1 , wherein said test lens is disposed in said second optical path from said eye to said physical target outside said first optical path from said wavefront sensor to said eye.  
     
     
         5 . The apparatus of  claim 1 , wherein said test lens is positioned an optical path length of approximately z o  from said physical target, said eye being adjusted to focus on said physical target said distance, z o , away from said eye.  
     
     
         6 . The apparatus of  claim 5 , wherein said test lens is positioned an optical path length of about z o −y o  from said physical target, where y o  corresponds to the optical path length from said test lens to said patient's eye.  
     
     
         7 . The apparatus of  claim 6 , wherein said optical path length distance, z o −y o , between said lens and said physical target is about 8 feet or greater.  
     
     
         8 . The apparatus of  claim 6 , wherein said distance, z−y o , between said lens and said physical target is about 20 feet.  
     
     
         9 . The apparatus of  claim 6 , wherein said distance, y o , between said eye and said test lens is between about 0.8 and 1.6 centimeters.  
     
     
         10 . The apparatus of  claim 6 , wherein said distance, y o , between said eye and said test lens is between about 0.5 and 4.0 centimeters.  
     
     
         11 . The apparatus of  claim 1 , further comprising a housing containing said wavefront measurement device, said housing including a substantial ly transparent window disposed in said second optical path between said patient's eye and said physical target such said patient's eye can focus on said physical target.  
     
     
         12 . The apparatus of  claim 11 , wherein said test lens is contained in said housing.  
     
     
         13 . The apparatus of  claim 1 , wherein said light source is selected from the group consisting of (i) a laser and (ii) a light emitting diode.  
     
     
         14 . The apparatus of  claim 1 , wherein said wavefront measurement device includes at least one light detector receiving the light returning from the patient's eye and sending a signal to at least one processor, said at least one processor generating at least one diagnostic output based on said wavefront measurements.  
     
     
         15 . A method of quantifying the quality of a person's vision, comprising: 
 providing a test lens through which said person views a physical target spaced from the test lens;    directing light into an eye of the person when the person looks through the test lens at said physical target, some of the light reflecting from tissue in said eye such that said light propagates through an ocular lens and cornea of said eye and exits said eye;    measuring a wavefront of said reflected light emanating from the person's eye;    determining one or more values of a figure of merit using said wavefront measurement, said figure of merit indicative of quality of a person's vision; and    producing a graphic based on said one or more values of said figure of merit, said graphic indicative of the quality of a person's vision.    
     
     
         16 . The method of  claim 15 , wherein said figure of merit comprises a function selected from the group consisting of a point spread function, a modulation transfer function, and an optical transfer function.  
     
     
         17 . The method of  claim 15 , wherein said figure of merit is selected from the group consisting of (i) a sum of terms based on Zernike coefficients and (ii) a weighted sum of terms based on Zernike coefficients.  
     
     
         18 . The method of  claim 17 , wherein said figure of merit includes a sum of squared Zernike coefficients.  
     
     
         19 . The method of  claim 15 , wherein said figure of merit comprises a Quality of Vision Factor (QVF) defined as  
       
         
           
             
               QVF 
               = 
               
                 ⅇ 
                 
                   - 
                   
                     ∑ 
                     
                       
                         P 
                         n 
                       
                       ⁢ 
                       
                         Z 
                         n 
                         2 
                       
                     
                   
                 
               
             
           
         
       
       wherein Z n  corresponds to coefficients for Zernike polynomials and P n  correspond to psychometric weight factors.  
     
     
         20 . The method of  claim 15 , wherein said graphic is selected from the group consisting of a pie chart, a bar chart, and a line chart.  
     
     
         21 . The apparatus of  claim 15 , wherein the graphic is color-coded in correspondence with said value of said figure of merit.  
     
     
         22 . The method of  claim 15 , wherein said graphic comprises an image of said target convolved with a function derived from wavefront measurement, said graphic appearing more distorted with increasing aberration.  
     
     
         23 . The method of  claim 22 , wherein said graphic comprises an image of said target convolved with a point spread function derived from wavefront measurement.  
     
     
         24 . The method of  claim 23 , wherein said point spread function is derived by squaring the magnitude of the Fourier transform of the wavefront.  
     
     
         25 . The method of  claim 15 , further comprising varying said test lens and determining said one or more figure of merit values for different lenses.  
     
     
         26 . The method of  claim 25 , further comprising identifying the lens that provides an extreme value of said figure of merit corresponding to a maximal quality of vision.  
     
     
         27 . The method of  claim 26 , wherein said extreme value comprises a peak average value of said figure of merit.  
     
     
         28 . The method of  claim 27 , wherein said extreme value comprises a maximum point spread function.  
     
     
         29 . The method of  claim 15 , further comprising directing said light through said test lens into said eye.  
     
     
         30 . The method of  claim 15 , further comprising situating said test lens such that said light is directed into said eye without passing through said test lens.  
     
     
         31 . A method of characterizing a person's vision, comprising: 
 (a) providing corrective optics for testing said vision, said corrective optics being variable to provide different amounts of optical correction;    (b) directing a light beam into an eye of the person, light from said light beam reflecting from tissue in said eye such that said light propagates through an ocular lens and cornea of said eye and exits said eye, said reflected light comprising a plurality of wavefronts;    (c) repetitively measuring said wavefronts emanating from the person's eye with said corrective optics adjusted to a substantially fixed amount of optical correction thereby producing a set of data points indicative of the quality of vision of the person for a given amount of optical correction; and    (d) determining the average and variation in said plurality of data points to provide an objective assessment of said correction.    
     
     
         32 . The method of  claim 31 , wherein said determining the variation in said plurality of data points comprises determining the standard deviation.  
     
     
         33 . The method of  claim 31 , further comprising comparing said variations and selecting an amount of optical correction based on said comparison.  
     
     
         34 . The method of  claim 33 , wherein the optical correction is selected substantially equal to the amount yielding the least variation.  
     
     
         35 . The method of  claim 33 , wherein the optical correction is selected substantially equal to the amount yielding the minimum standard deviation.  
     
     
         36 . The method of  claim 31 , wherein said reflected light emanating from the person's eye is repetitively measured for an amount of optical correction such that the time period between the repeat measurements is sufficiently long to permit the eye to adjust its focus.  
     
     
         37 . The method of  claim 36 , wherein said time period between repeat measurements ranges between about 0.1 to 5 seconds.  
     
     
         38 . The method of  claim 31 , wherein said corrective optics comprises a plurality of test lens in a phoropter system.  
     
     
         39 . The method of  claim 31 , wherein said corrective optics comprises an optical system having variable optical power.  
     
     
         40 . The method of  claim 31 , further comprising selecting the amount of optical correction for said person based as least in part on the optical correction that yields reduced aberration in said wavefronts.  
     
     
         41 . The method of  claim 40 , further comprising selecting the amount of optical power that provides a peak value of a figure of merit on the quality of vision of the patient.  
     
     
         42 . The method of  claim 31 , wherein said optical correction selected is substantially equal to an amount between the optical correction yielding the least variation and the optical correction yielding the peak value of figure of merit on the quality of vision.  
     
     
         43 . An apparatus for automatically determining correction for a patient's vision, said apparatus comprising: 
 test optics for testing said vision, said test optics being variable to provide different amounts of optical correction;    a light source and associated optics for directing light into an eye of the patient, said light reflecting from tissue in said eye, said reflected light comprising a plurality of wavefronts that propagate through an ocular lens and cornea in said eye;    a wavefront sensor including one or more optical detectors for measuring said wavefronts emanating from the patient's eye, said wavefront sensor having an electrical output representative of said wavefront;    an electrical processor configured to receive said electrical output from said wavefront sensor and determine the quality of said patient's vision therefrom; and    a mechanical actuator electrically connected to said processor, said mechanical actuator adjusting the test optics so as to vary the amounts of optical correction.    
     
     
         44 . The apparatus of  claim 43 , further comprising a computer readable medium having a program of instructions stored thereon for causing said electrical processor to execute method steps for determining the quality of said patient's vision, comprising: 
 (a) calculating a value of a figure of merit indicative of the patient's quality of vision, said value being derived at least in part from a measurement of one of the wavefronts from the patient's eye;    (b) retrieving another wavefront measurement from the wavefront sensor;    (c) repeating steps (a) and (b) N times;    (c) calculating the average and variation of the figure of merit values and storing the average and variation as a data set for a given optical correction;    (d) instructing the actuator to alter the test optics to provide a different optical correction;    (e) repeating steps (a) through (d) until a predetermined end point has been reached; and    (f) selecting the optical correction that yields (i) the maximum average value of the figure of merit, (ii) the minimum variation of the figure of merit, or (iii) a value between those of (i) and (ii).    
     
     
         45 . The apparatus of  claim 43 , further comprising a display electrically connected to said electrical processor so as to receive input from said electrical processor such that said electrical processor can output results of said measurements to said display.  
     
     
         46 . The apparatus of  claim 45 , wherein said electrical processor and display are configured to provide a graphical representation of a target image as seen by the patient, said graphical representation generated by a convolution of said target image with a function derived from said wavefront measurements, said image being distorted an amount indicative of distortion in the patient's vision.  
     
     
         47 . The apparatus of  claim 45 , wherein said electrical processor and display are configured to provide information selected from the group consisting of (1) a numerical and/or graphic representative of the effectiveness of application of different amount of optical power; and (2) a numerical and/or graphic display of the contrast function of the patient's vision.  
     
     
         48 . The apparatus of  claim 43 , wherein said electrical processor includes electronic circuitry configured to select a prescription suitable for correction and an output for outputting said prescription.  
     
     
         49 . The apparatus of  claim 43 , wherein said test optics comprise a plurality of test lens that can be separately introduced into an optical path between the patient's eye and a target to adjust the patient's vision.  
     
     
         50 . A method of determining correction for a person's vision, comprising: 
 directing light into an eye of the person, said light reflecting from tissue in said eye, said reflected light comprising a plurality of wavefronts that propagates through an ocular lens and cornea in said eye;    measuring said wavefronts with a wavefront sensor;    representing at least one of said wavefronts by a sum of orthogonal components,      εK n Q n ,    where Q n  corresponds to said orthogonal components and K n  corresponds to coefficients having values selected to substantially match said sum with said wavefront;    weighting said orthogonal components with psychometric weight factors P n  based on the relative influence of the orthogonal component Q n  on human vision; and    designing optical correction based on said wavefront representation and said psychometric weight factors.    
     
     
         51 . The method of  claim 50 , wherein said orthogonal components comprise Zernike polynomials.  
     
     
         52 . The method of  claim 50 , wherein said psychometric weight factors P n  is obtained from a normative data base generated by quantifying the effects of the respective orthogonal components Q n  in a normative population group.  
     
     
         53 . A method of quantifying accommodation in an eye having a cornea, an ocular lens, and a retina, said method comprising: 
 directing a light beam into the eye, light from said light beam reflecting from tissue in said eye such that said light propagates through the ocular lens and cornea of said eye and exits said eye;    repetitively measuring wavefronts associated with said reflected light emanating from the eye for a set of conditions that induce an amount of accommodation, thereby producing a set of data points indicative of the quality of vision for said plurality of wavefronts measured under said set of conditions; and    determining the average and variation in said plurality of data points to provide a measurement of the amount of accommodation.    
     
     
         54 . The method of  claim 53 , further comprising repeating said measuring and determining steps for different sets of conditions for inducing different amounts of accommodation, thereby producing a plurality of average values which if plotted form a curve having a maximum.  
     
     
         55 . The method of  claim 53 , further comprising providing at least one target a distance from said eye.  
     
     
         56 . The method of  claim 55 , wherein said first set of conditions includes a first target distance and said second set of conditions includes a second target distance, said first and second target distances being different so as to introduce different amounts of accommodation.  
     
     
         57 . The method of  claim 53 , further comprising providing optics through which said eye can view at least one target, said optics having spherical power to move the image of the target behind the retina.  
     
     
         58 . The method of  claim 54 , further comprising providing optics through which said eye can view at least one target, said optics having spherical power to move the image of the target behind the retina.  
     
     
         59 . The method of  claim 58 , wherein said maximum is a plateau having a width, said method further comprising determining the accommodating power of a person from the width of the plateau in units of optical power.  
     
     
         60 . The method of  claim 53 , wherein said determining the variation in said plurality of data points comprises determining the standard deviation from the data points.  
     
     
         61 . A computer readable medium having a program of instructions stored thereon for causing an electrical processor to execute method steps for identifying optical correction for a person's eye based on wavefront measurements of light reflected from said person's eye, comprising: 
 (a) calculating a value of a figure of merit indicative of the person's quality of vision, said value being derived at least in part from a measurement of a wavefront from said person's eye;    (b) retrieving another wavefront measurement;    (c) repeating steps (a) and (b) N times;    (c) calculating the average and variation of the figure of merit values and storing the average and variation as a data set for a given optical correction;    (d) repeating steps (a) through (d) for different optical correction; and    (e) selecting the optical correction that yields (i) the maximum average value of the figure of merit, (ii) the minimum variation of the figure of merit, or (iii) a value between those of (i) and (ii).    
     
     
         62 . The method of  claim 41 , the figure of merit on the quality of vision of the patient being selected from the group consisting of (a) QVF, defined as  
       
         
           
             
               QVF 
               = 
               
                 ⅇ 
                 
                   - 
                   
                     ∑ 
                     
                       
                         P 
                         n 
                       
                       ⁢ 
                       
                         Z 
                         n 
                         2 
                       
                     
                   
                 
               
             
           
         
       
       wherein Z n  corresponds to coefficients for Zernike polynomials and P n  correspond to psychometric weight factors, (b) a point spread function, and (c) a sum of squared Zernike coefficients.