Tear film interferometry measures the thickness of the lipid layer of the tear film. A broad spectrum light is shined on the tear film, and the reflection is examined with an interferometer (a device that measures interference). Differences in lipid layer thickness reflect as different colors, according to the following table.
| Color | LLT (nm) | Munsell color standard notation |
|---|---|---|
| White | 30 | N 9/0 |
| Grey (white) | 45 | N 8.5/0 |
| Grey | 60 | N 8/0 |
| Grey (yellow) | 75 | 10 YR 9/2 |
| Yellow | 90 | 10 YR 9/4 |
| Yellow (brown) | 105 | 7.5 YR 8/6 |
| Brown (yellow) | 120 | 7.5 YR 7/10 |
| Brown | 135 | 2.5 YR 6/10 |
| Brown (blue) | 150 | 7.5 PB 8/2 |
| Blue (brown) | 165 | 2.5 PB 7/4 |
| Blue | 180 | 2.5 PB 6/4 |
Reference
Correlation of lipid layer thickness measurements with fluorescein tear film break-up time and Schirmer’s test
M A Isreb, J V Greiner, D R Korb, T Glonek, S S Mody, V M Finnemore, C V Reddy
Eye
(2003) 17, 79–83. 10.1038/sj.eye.6700224
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