Measurement of the lipid and aqueous layers of a tear film

Abstract

Systems and methods for determining thickness of lipid and aqueous layers of a tear film in which a spectrum array is generated from optical coherence tomography and input into a statistical estimator, which determines the thickness of the lipid and/or aqueous layers at a nanometer resolution based on the inputted spectrum and other information, such as information about a laser intensity noise, Poisson noise, and dark noise associated with the OCT.

1 . A method of determining thickness of lipid and aqueous layers of a tear film, the method comprising:
 directing light from a light source to an eye, the eye having a tear film including a lipid layer and an aqueous layer;   collecting light at a light detector, the collected light including back-reflected light from the eye;   generating a spectrum array based on the light collected at the light detector;   inputting the spectrum array into a statistical estimator comprising a processor and a memory;   at the statistical estimator, determining at least one of a lipid layer thickness and an aqueous layer thickness for the lipid and aqueous layers based on the inputted spectrum array.   
     
     
         2 . The method of  claim 1 , wherein determining at least one of the lipid and aqueous layer thicknesses comprises determining both the lipid layer thickness and the aqueous layer thickness. 
     
     
         3 . The method of  claim 2 , wherein collecting light at the light detector comprises collecting light at a spectrometer. 
     
     
         4 . The method of  claim 3 , wherein the light source and the spectrometer are components of an optical coherence tomography system, the optical coherence tomography system comprising an axial point spread function for a corneal epithelium of 2 μm or less. 
     
     
         5 . The method of  claim 4 , wherein the determined lipid and aqueous layer thicknesses are determined at a nanometer scale. 
     
     
         6 . The method of  claim 3 , wherein the light source and the spectrometer are components of an optical coherence tomography system, the optical coherence tomography system comprising an axial point spread function for a corneal epithelium of between 0.75 μm and 1.25 μm. 
     
     
         7 . The method of  claim 2 , wherein the generated spectrum array comprises an array with a plurality of elements in which at least some of the elements are each proportional to a number of electrons accumulated at a location on the light detector over a time segment. 
     
     
         8 . The method of  claim 7 , wherein the statistical estimator determines the lipid and aqueous layer thicknesses based on the inputted spectrum array and at least one of a quantified intensity noise of the light source, a quantified Poisson noise of the light detector, and a quantified dark noise of the detector. 
     
     
         9 . The method of  claim 7 , wherein the statistical estimator determines the lipid and aqueous layer thicknesses based on the inputted spectrum array, an intensity noise of the light source, a Poisson noise of the light detector, and a dark noise of the detector. 
     
     
         10 . A system for estimating tear film thickness comprising:
 an optical coherence tomography component configured to generate data about a tear film; and   a statistical estimator component configured to generate an estimate of an aqueous layer thickness and an estimate of a lipid layer thickness of the tear film based on the generated data.   
     
     
         11 . The system of  claim 10 , wherein the optical coherence tomography component includes a light source, a beam splitter, a reference arm, a sample arm, and a detector. 
     
     
         12 . The system of  claim 11 , wherein the light source is a broadband source and wherein the detector is a spectrometer. 
     
     
         13 . The system of  claim 12 , wherein the statistical estimator component generates the estimates based on the generated spectrum. 
     
     
         14 . The system of  claim 13 , wherein the statistical estimator is at least one of a maximum-likelihood estimator, a maximum posteriori estimator, or a posterior mean estimator. 
     
     
         15 . The system of  claim 10 , wherein the optical coherence tomography component is a micron axial resolution optical coherence tomography component and wherein the statistical estimator component is a nanometer resolution statistical estimator. 
     
     
         16 . The system of  claim 10 , wherein the statistical estimator component includes a processor and a memory. 
     
     
         17 . A system for estimating tear film thickness comprising:
 a micron axial resolution optical coherence tomography component configured to generate data about a tear film; and   a nanometer resolution statistical estimator component configured to generate a nanometer resolution estimate of a tear film thickness based on the generated data.   
     
     
         18 . The system of  claim 17 , wherein the nanometer resolution statistical estimator component is configured to generate the nanometer resolution estimate based on the generated data and based on data on light source noise and detector noise. 
     
     
         19 . The system of  claim 17 , wherein the nanometer resolution statistical estimator component is configured to generate an estimate of nanometer resolution lipid layer thickness and a separate estimate of aqueous layer thickness based on the generated data. 
     
     
         20 . The system of  claim 17 , wherein the optical coherence tomography component comprises an axial point spread function for a corneal epithelium of 2 μm or less. 
     
     
         21 . The system of  claim 17 , further comprising an eye tracker component configured to record information about an eye movement during data generation by the optical coherence tomography component.