Eye examination apparatus employing polarized light probe

Abstract

Apparatus is provided for determining the topography, thickness, and fiber orientation of the nerve fiber layer at the fundus of the eye by measuring the polarization shift induced in a return beam of polarized light which is reflected at the ocular fundus from an incident beam of a known polarization state. A corneal polarization compensator effectively cancels the birefringent effects of the cornea and other portions of the eye anterior to the fundus, so that clinically meaningful results are produced. A method for directing a measurement beam into the eye is also disclosed.

What is claimed is:  
     
         1 . An apparatus for analyzing an eye having an anterior portion and a posterior portion, comprising: 
 (a) a polarized light source for producing an incident diagnostic beam of known state of polarization;    (b) an optics system transmitting said incident diagnostic beam into an eye through the pupil, where it is reflected from the interior of the eye as a return diagnostic beam, the optics system collecting said return diagnostic beam and directing same to a polarization sensitive detection device;    (d) a polarization sensitive detection device for collecting and transducing information about the state of polarization of said return diagnostic beam into an electrical signal, the electrical signal being representative of the state of polarization of the return diagnostic beam whereby the electrical signal can be used to indicate the state of polarization of the return beam; and    (e) a transmitting circuit receiving the electrical signal and transmitting the signal to a computer.    
     
     
         2 . The apparatus of  claim 1 , further comprising a corneal polarization compensator positioned and configured for modifying the polarization of at least one of said diagnostic beams to thereby facilitate assessment of any alteration of the polarization state of said return diagnostic beam caused by the polarization properties of the posterior portion of the eye.  
     
     
         3 . The apparatus of  claim 1 , further comprising a computer electrically connected to the detection device and including logic means for directing the diagnostic beam onto an eye of a patient, the logic means including: 
 means for receiving an image signal representative of an image of a fundus of the patient, the signal being derived from the diagnostic beam, the fundus including an optic nerve location; and    means for identifying the optic nerve location.    
     
     
         4 . The apparatus of  claim 3 , wherein the optics system includes at least one focussing lens and the logic means further comprise means for generating a focus signal for use thereof in moving the focussing lens to focus the diagnostic beam onto the optic nerve location.  
     
     
         5 . The apparatus of  claim 4 , wherein the fundus includes nerve fibers defining respective widths, and the means for generating a focus signal causes the focussing lens to move such that the widths are minimized in the image signal.  
     
     
         6 . The apparatus of  claim 1 , wherein the computer is remote from the optics system, and the computer accesses a normative database to compare the electrical signal to at least some elements in the database and to generate an analysis signal in response thereto  
     
     
         7 . The apparatus of  claim 1 , wherein the computer is local to the optics system, and the computer accesses a removable computer memory device containing a normative database to compare the electrical signal to at least some elements in the database and to generate an analysis signal in response thereto.  
     
     
         8 . A computer program device comprising: 
 a computer program storage device readable by a digital processing apparatus; and    a program means on the program storage device and including instructions executable by the digital processing apparatus for performing method steps for directing a diagnostic beam onto an eye of a patient, the method steps comprising: 
 receiving an image signal representative of a fundus of the eye, the fundus including an optic nerve location; and  
 in response to the image signal, generating one or more images of the eye, at least one of the images being centered on the optic nerve location in response to the image signal.  
   
     
     
         9 . The computer program device of  claim 8 , wherein the image signal has an intensity, and the method steps include generating at least one control signal in response to the image signal, at least one of the control signals being a focus signal for causing a focussing lens to move such that the intensity of the image signal is maximized.  
     
     
         10 . The computer program device of  claim 9 , further comprising a computer accessing a normative database to compare the image signal to at least some elements in the database and to generate an analysis signal in response thereto.  
     
     
         11 . The computer program device of  claim 10 , further comprising a removable computer memory device containing the normative database.  
     
     
         12 . A method for diagnosing maladies of an eye, comprising: 
 directing at least one guide beam toward a pupil of the eye;    transmitting at least one diagnostic beam along the guide beam;    receiving at least one reflection of the diagnostic beam;    transforming the reflection into an image signal; and    based on the image signal, focussing the diagnostic beam onto an optic nerve location in the eye.    
     
     
         13 . The method of  claim 12 , further comprising identifying the optic nerve location in the image signal, and producing an image of the eye centered on the optic nerve location in response thereto.  
     
     
         14 . The method of  claim 13 , comprising: 
 providing an optics system including at least one focussing lens; and    generating a focus signal for use thereof in moving the focussing lens to focus the diagnostic beam onto the optic nerve location.    
     
     
         15 . The method of  claim 14 , wherein the image signal has an intensity, and at least one of the control signals is a focus signal for causing a focussing lens to move such that the intensity of the image signal is maximized.  
     
     
         16 . The method of  claim 12 , further comprising accessing a normative database to compare the image signal to at least some elements in the database and to generate an analysis signal in response thereto.  
     
     
         17 . The method of  claim 16 , wherein the comparison is undertaken at a location remote from the eye.  
     
     
         18 . In a diagnostic system using polarized light in the diagnosis of eye disease, an anterior eye segment polarization compensator comprising: 
 (a) a source of light for producing an incident compensation beam in a known state of polarization;    (b) a transmitting means for directing said incident compensation beam through the anterior segment of the eye to be reflected by regions of the eye more anterior than the cornea, to form a reflected compensation beam exiting the eye along an optical pathway substantially aligned with the incident compensation beam; and,    (c) a variable retarder optically interposed in said optical pathway.    
     
     
         19 . A compensator according to  claim 18  and including compensator monitoring means to determine the degree of combined polarization shift from said incident compensation beam as it double-passes the variable retarder and the anterior segment of the eye to exit said variable retarder as said reflected compensation beam, such that any alteration of the state of polarization of said reflected beam from the state of polarization of said incident beam caused by the anterior segment of the eye can be neutralized by adjusting said variable retarder.  
     
     
         20 . The compensator according to  claim 18  and including a polarizing beamsplitter, and said incident compensation beam is linearly polarized by being passed through said polarizing beamsplitter from a first side thereof, and said reflected beam is reflected from a second side of said polarizing beamsplitter and focused on a photodetector and including a quarter-wave retarder in said optical passageway such that when said variable retarder is set properly, said photodetector detects maximum intensity when said variable retarder has compensated for the polarization of said anterior segment if the eye.  
     
     
         21 . The compensator according to  claim 20  and including a reticulated diffraction grating disposed in the incident compensation beam to fragment said incident compensation beam into a plurality of sub-beams.  
     
     
         22 . The compensator according to  claim 18  and including a polarization sensitive device comprising an ellipsometer emitting an incident diagnostic beam along a path through said variable retarder and which is reflected as a return diagnostic beam, and said diagnostic beams and said compensation beams have substantially coincident paths through the variable retarder and the anterior segment of the eye, such that the return diagnostic beam is automatically polarization-state adjusted to compensate for any alteration of polarization state caused by the anterior portion of the eye.  
     
     
         23 . The compensator according to  claim 22  wherein said polarization sensitive device includes a light source for producing a polarized beam, and means to scan said polarized beam across the retinal nerve fiber layer of the eye, causing the reflection of a return diagnostic beam, and including an array of polarizers of progressive levels of polarization which are sequentially illuminated by said return diagnostic beam, and means for directing said return diagnostic beam, after passing said polarizers, to said polarization sensitive detection device for detection of the state of polarization.  
     
     
         24 . The compensator according to  claim 18  and including a polarization sensitive device comprising a tomographic probe having a three-dimensional scanner and an analyzer and detector to filter out return light reflected from the nerve fiber layer which has been altered in polarization and an analyzer to analyze the return light that has not been altered in polarization, and means to display a topographic map of the nerve fiber layer based on an analysis of geometric points of the nerve fiber layer producing non-polarization-altered return light.  
     
     
         25 . The apparatus of  claim 3 , further comprising means for generating a steering signal for use thereof in directing the diagnostic beam onto the optic nerve location.