Thermal characterization of lipid and aqueous layers on tear film

Tear film is composed of three layers: mucin, aqueous, and lipid; their integrity is essential for good eye function. A setup was implemented to acquire infrared image sequences from both eyes of each of the 48 participants, 23 with DED and 25 without it. The acquisition time and period were controlled to achieve a correct time scale in each blinking, and a spectral filter in the range of 9 to 10 μm was used to enhance the spectral resolution. The evaporation rate, related to the aqueous layer thickness, is computed by measuring energy on an infrared image sequence, observing that the exponential growth constantly changes with the thinnest of aqueous layers. When dry eye disease persists for a long time, the lipid layer becomes thicker, which can be characterized by a change in the thermal emissivity of the tear film. It is possible to evaluate the tear film integrity by changes in the energy emission in two blinking moments in an innocuous and efficient way. To corroborate the results, the infrared measurements were compared with measurements of tear meniscus height using a slit lamp and Schirmer tear test.