Method for calculating tear film lipid and aqueous layer thickness and corneal surface refractive index from interferometry data
View Patent ↗Disclosed herein is a method of calculating tear film lipid and aqueous layer thicknesses and/or corneal surface refractive index from interferometry data obtained from simultaneous measurements of the aqueous and lipid layers of the tear film along with a measurement of the corneal surface reflectance.
1. A method of evaluating an ocular environment of a patient comprising:
(a) selecting the patient;
(b) aligning an eye of the patient with light originating from a light source;
(c) measuring light reflectance from the eye;
(d) fitting the light reflectance to a mathematical construct based upon a characteristic mathematical matrix of a thin film stack comprising in sequence from top to bottom: air as a boundary, a tear film lipid layer, a tear film aqueous layer and a corneal epithelium as a semi-infinite substrate; and
(e) determining a parameter selected from the group consisting of lipid layer thickness, aqueous layer thickness and corneal surface refractive index.
2. The method of claim 1 , wherein the light reflectance is from the tear film, the ocular surface or a combination thereof.
3. The method of claim 1 , wherein the determined parameter is compared to a reference value.
4. The method as in claim 1 , wherein the measuring is performed using an interferometer.
5. The method as in claim 1 , wherein the method includes adjusting the mathematical construct based on a factor selected from the group consisting of (a) an adjustment for tear film and ocular surface light reflectance and (b) an adjustment for substrate roughness.
6. The method as in claim 3 , wherein the adjustment for tear film and ocular surface light reflectance is a number.
7. The method as in claim 5 , wherein the adjustment for substrate roughness is selected from mathematical terms comprising exp(−cc*1000/λ) and exp(−a*1000/λ)+b*1000/λ)^2), wherein cc, a and b are numbers.
8. The method as in claim 5 , wherein the adjustment for substrate roughness is selected from mathematical terms comprising a non-Gaussian height distribution function or term.
9. A method of evaluating an ocular environment of a patient comprising the steps of:
(a) selecting the patient;
(b) aligning an eye of the patient with light originating from a light source;
(c) measuring light reflectance of the eye;
(d) fitting the light reflectance to a mathematical construct based upon a characteristic mathematical matrix of a thin film stack comprising in sequence from top to bottom: air as a boundary, a tear film lipid layer, a tear film aqueous layer and a corneal surface as a semi-infinite substrate;
(e) determining a first parameter selected from the group consisting of lipid layer thickness, aqueous layer thickness and corneal surface refractive index; and
(f) comparing the first parameter with known parameters for patients with known tear film or ocular surface characteristics.
10. The method as in claim 9 , wherein the measurement of light reflectance is performed using an interferometer.
11. The method as in claim 9 , wherein the method includes adjusting the mathematical construct based on a factor selected from the group consisting of (a) an adjustment for tear film and ocular surface light reflectance and (b) an adjustment for substrate roughness.
12. The method as in claim 11 , wherein the adjustment for tear film and ocular surface light reflectance is a number.
13. The method as in claim 11 , wherein the adjustment for substrate roughness is selected from mathematical terms comprising exp(−cc*1000/λ) and exp(−a*1000/λ)+b*1000/λ)^2), wherein cc, a and b are numbers.
14. The method as in claim 11 , wherein the adjustment for substrate roughness is selected from mathematical terms comprising a non-Gaussian height distribution function or term.
15. A method of evaluating an ocular environment of a patient comprising the steps of:
(a) selecting the patient;
(b) aligning an eye of the patient with light originating from a light source;
(c) measuring light reflectance from the eye;
(d) fitting the light reflectance to a mathematical construct based upon a characteristic mathematical matrix of a thin film stack comprising in sequence from top to bottom: air as a boundary, a tear film lipid layer, a tear film aqueous layer and a corneal epithelium as a semi-infinite substrate; and
(e) calculating at least one of (a) tear film lipid layer thickness, (b) tear film aqueous layer thicknesses, and (c) refractive index of the corneal surface of the patient using the mathematical construct.
16. The method as in claim 15 , wherein the measurement of light reflectance is performed using an interferometer.
17. The method as in claim 15 , wherein the method includes adjusting the mathematical construct based on a factor selected from the group consisting of (a) an adjustment for tear film and ocular surface light reflectance and (b) an adjustment for substrate roughness.
18. The method as in claim 17 , wherein the adjustment for tear film and ocular surface light reflectance is a number.
19. The method as in claim 17 , wherein the adjustment for substrate roughness is selected from mathematical terms comprising exp(−cc*1000/λ) and exp(−a*1000/λ)+b*1000/λ)^2), wherein cc, a and b are numbers.
20. The method as in claim 17 , wherein the adjustment for substrate roughness is selected from mathematical terms comprising a non-Gaussian height distribution function or term.