METHOD AND DEVICE FOR IN VIVO WETTING DETERMINATIONS

A method for evaluating the in vivo ability of a contact lens to become or remain wet includes the steps of supporting the subject's head to determine a fixed orientation of the lens, illuminating the lens with coherent light, imaging the pre-lens tear film in a manner to form an interference pattern, recording in a time sequence manner the image formed thereby, and determining the tear film thickness by correlating the interference bands of the recorded image. The classical contact angle is derived, and other measures, such as the time interval from blink until the onset of tear film breakup, or the time until the film evaporates, and the initial or average film thickness are derived. In addition, the nature and evolution of localized dry spots may be directly observed, clarifying the causes of tear film breakdown on worn contact lenses. The invention includes methods for the evaluation of wetting characteristics as they are affected by lens material, lens aging and lens soiling, as well as the evaluation of solvents, additives and cleaners, for their effects on wetting characteristics. Apparatus for performing the method include a means for supporting the head so as to determine a fixed location of the contact lens, a coherent light source, and a camera focused at the pre-lens film from a position to image light from the source specularly reflected from the front and rear surfaces of the tear film. A film motion analyzer provides numerical coordinates of interference bands, and a microprocessor analyses the coordinates to provide a quantitative measure of lens position or wetting characteristics.