Ophthalmic Refractor and Method of Ophthalmic Refractor Signal Analysis

Abstract

An ophthalmic refractor is described that provides a non-linear relationship between spherical power and refractive error by positioning a reference plane for a sensor system of the refractor in front of the cornea. The refractor may have a working distance and dynamic range that enable it to be mounted on a surgical microscope. Also described are computational methods for analysing the output from the ophthalmic refractor, utilising error minimisation, linear regression and Fourier Transform analysis.

1 . An ophthalmic refractor comprising optical components for receiving return beam of light from a subject eye and detecting a wavefront of the return beam of light, the optical components comprising:
 A sensor system comprising a lenslet array and a light detector, the lenslet array focusing light onto the light detector; and   A relay lens system disposed along an optical path of the return beam of light between the sensor system and a location for the anterior cornea of a subject eye, the relay lens system imaging a reference plane onto the lenslet array;   wherein the relay lens is position and has a focal length son that he reference plane is located in front of the location for the anterior cornea of the subject eye.   
     
     
         2 . The ophthalmic refractor of  claim 1  wherein the relay lens is non-telescopic. 
     
     
         3 . The ophthalmic refractor of  claim 1  having a working distance selected from within the range 175 mm to 250 mm (inclusive). 
     
     
         4 . The ophthalmic refractor of  claim 1 , wherein the reference plane is 100 mm or less from the location for the anterior cornea. 
     
     
         5 . The ophthalmic refractor of  claim 1 , wherein the reference plane is 75 mm or less from the location for the anterior cornea. 
     
     
         6 . The ophthalmic refractor of  claim 1 , wherein the reference plane is 50 mm or less from the location for the anterior cornea. 
     
     
         7 . The ophthalmic refractor of  claim 1 , wherein the reference plane is 25 mm or less from the location for the anterior cornea. 
     
     
         8 . The ophthalmic refractor of  claim 1 , wherein the relay lens has a unity magnifying power. 
     
     
         9 . The ophthalmic refractor of  claim 1 , wherein the relay lens has a magnifying power greater than unity. 
     
     
         10 . The ophthalmic refractor of  claim 1  wherein:
 the refractor has a working distance selected from within the range of 175 mm to 250 mm (inclusive) and wherein the reference plane is 100 mm or less from the location for the anterior cornea. 
 
     
     
         11 . A method for measuring ophthalmic refractive error, the method comprising:
 utilising a relay system to image wavefront of a return light beam from a subject eye onto a Hartmann-Shack sensor system at a location in front of the cornea, so as to provide a non-linear relationship between spherical power and refractive error;   utilising a computational system to receive from the Hartmann-Shack sensor system a spot distribution and compute a value indicative of the refractive error.   
     
     
         12 . The method of  claim 11 , wherein utilizing a computational system to receive from the Hartmann-Shack sensor system a spot distribution and compute a value indicative of the refractive error comprises utilising the computation system to compensate for said non-linear relationship. 
     
     
         13 . The method of  claim 11  further comprising one of continuously or intermittently repeating said processes of utilising a relay system and utilising a computational system. 
     
     
         14 . A method of analysing wavefront data generated by a Hartmann-Shack sensor system with a non-linear relationship between spherical power and refractive error, the method comprising, in a computational system:
 performing linear regression on centroid positions of spots defined by the wavefront data in at least two different directions to compute a slope value for each said direction;   utilising the computed slope values to compute and output a value for at least one of the group comprising M, J 0  and J 45  vectors for the subject eye.   
     
     
         15 . The method of  claim 14 , wherein utilising the computed slope values comprises solving a set of simultaneous equations comprising as variables the slope values and M, J 0  and J 45  vectors. 
     
     
         16 . The method of  claim 14  further comprising:
 running an error minimisation algorithm to find coefficients of a function defining the difference in position between centroids of spots defined by the wavefront data and reference centroid positions, wherein the reference centroid positions compensate for the non-linear relationship and wherein the coefficients are defined so as to have a known mathematical relationship to said M, J 0  and J 45  vectors. 
 
     
     
         17 . The method of  claim 14  further comprising:
 computing a frequency domain transformation of the wavefront data; 
 computing the frequency of at least one centroid of the transformed wavefront data. 
 
     
     
         18 . (canceled) 
     
     
         19 . (canceled) 
     
     
         20 . The ophthalmic refractor of  claim 1  further comprising a base for mounting one or more of the optical components, wherein the relay lens system comprises a relay component configured to protrude at least partially through the base thereby reducing at least one dimension of the ophthalmic refractor. 
     
     
         21 . The ophthalmic refractor of  claim 20  wherein the relay lens system interfaces with an operation microscope, the microscope having a central sagittal plane; and
 wherein the relay component is configured so that an optical axis of the ophthalmic refractor is at 45 degrees from the central sagittal plan of the microscope. 
 
     
     
         22 . The ophthalmic refractor of  claim 21  further comprising a mounting interface with the operation microscope, the mounting interface comprising a reconfigurable mounting assembly for optical alignment between the ophthalmic refractor and the microscope.