Quantifying the pre-corneal tear film thickness and its components

Tear film stability and its interaction with the corneal surface play an important role in maintaining ocular surface integrity and quality of vision. Dry Eye Syndrome (DES) refers to abnormalities of tear film secretion and/or stability diagnosed by conventional methods such as the Schirmer test and tear break-up time (TBUT). Several different physical methods have been developed to measure non-invasively the structure and function of the tear film including high-speed videokeratography and dynamic wavefront aberrometry. Interferometry and optical coherence tomography are amongst new proposed methods to measure tear film thickness that have remained in research phase due to their complex, bulky and expensive instrumentation.;Here we present Fluctuation Analysis of Spatial Image Correlation (FASIC), a non-invasive method for evaluating the complex dynamics of the tear film surface by spatial correlation analysis. With this technology, a series of images are obtained using a laser illumination and a cMOS camera. The spatial auto-correlation is calculated for every frame. We have developed a mathematical model to obtain the thickness of the tear film from the sinusoidal background which appears in the spatial auto-correlation image. The model includes the macroscopic dynamics of small lipid droplets in the tear film. Consistent data with live animal model and human clinical study has been obtained.