Diagnosis of Dry Eye - Basic Study With Simulated Tear Film Behavior on a Model Eye

Abstract

Purpose: : To build up a model of the human cornea and the tear film. Furthermore a measurement setup to analyze the dynamic behavior of the artificial tear film as well as its break-up has to be designed.

Methods: : A physical model of the human anterior corneal surface including the tear film has been developed. For this purpose a homogeneous tear film layer on a metal sphere was achieved by lowering a liquid level in a basin. After a certain time interval that artificial tear film broke up simulating the physiological conditions of dry eye syndrome.Two CCD cameras were integrated in a measurement setup. Using a beam splitter the simulated tear film was recorded simultaneously on a common axis. Each camera followed a different concept:1) A grid pattern was projected on the tear film, which operated as a convex mirror. The first camera focused on the occurring virtual image, which is located behind the surface of the liquid film. This was used to analyze the temporal progression of the liquid film and should replicate the evaporation in human eyes before the tear film breaks up.2) The second camera focused on the anterior surface of the liquid. With this method the exact time point of liquid film break-up was determined from the change in reflective properties at the break-up area. This resembles the scattering effect on the mucin layer during physiologic tear film break-up.

Results: : The setup allowed for observation of the dynamic behavior of the simulated tear film and its break-up with two different concepts. The recordings from both cameras could be compared directly in contrast to apply both concepts consecutively. The first camera monitored the change of the grid pattern image due to the temporal progression of the liquid film before break-up. The second camera detected the location and time point of the tear film break-up due to the changed brightness.

Conclusions: : The spatial and temporal dynamics of the model eye’s liquid surface were detectable. A combination of both concepts is suitable to analyze tear film characteristics in human eyes. For in-vivo measurements saccades have to be taken into account to avoid motion artifacts. We consider this approach to be usable in clinical practice as non-invasive measurement tool for diagnosis of dry eye syndrome. Automation of our diagnosis tool could be achieved by using wavelet transform of the monitored data sequences.

Keywords: cornea: tears/tear film/dry eye