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22 December 1989 Interferometric Measurement Of In-Vivo Contact Lens Wetting
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By observing the specular reflectance of monochromatic light from the anterior and posterior boundaries of the tear film on the front surface of a contact lens, optical conditions can be met which allow the observation of interference fringe patterns. Such patterns permit the thickness distribution of the pre-lens tear layer to be seen over a sizable area of the curved lens surface. Since the resulting interference pattern is analogous to a topographical map of the tear film thickness, but which is changing rapidly with time, continuous observation and recording of the patterns allow detailed information to be obtained concerning the time course and dynamics of tear film flow, thinning, and breakup during the interblink periods associated with normal blinking. With a contact lens of a given material, evaporation of the thin anterior tear layer was thought to be the major factor causing lens drying. Use of the tear film interferometer indicates that while this is usually the case for soft, hydrophilic lenses, both hard and rigid gas permeable (RGP) lenses have much shorter tear film breakup times largely independent of evaporative effects. The prelens tear fluid can be seen to be drawn off as a continuous sheet by the fluid in the tear menisci along the upper and lower lid margin due to surface tension differences, as long as continuity exists between the prelens tear film and either meniscus. This meniscus effect acts more rapidly than thinning by evaporation, and appears to be the primary factor determining the length of time hard or RGP lens surface will remain wet during interblink periods.
© (1989) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Marshall G. Doane "Interferometric Measurement Of In-Vivo Contact Lens Wetting", Proc. SPIE 1161, New Methods in Microscopy and Low Light Imaging, (22 December 1989);

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