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Bo Tan, Yixiu Zhou, Tiffany Yuen, Andrew D Graham, Gavriil Tsechpenakis, Meng C Lin; Fluorogram of post-lens tear mixing under soft contact lenses. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4667.
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To quantify 2-D fluorescence pattern (fluorogram) of the post-lens tear film using a modified slit lamp and novel image processing technique, and to explore the influence of ocular shape and lens fit on post-lens tear mixing with soft contact lenses.
Eleven subjects participated in a randomized crossover study with three types of soft lenses: Acuvue Oasys (AO), Air Optix Night and Day (N&D), and Biofinity (BIO). 3μL of 7% FITC-Dextran (mw=10,000) was instilled onto the concave surface of each study lens prior to lens insertion. The optics of a slit lamp were modified to remove corneal Purkinje image and expand the illuminated area on the cornea, and post-experiment image processing was employed to minimize the influence of uneven illumination. Images were taken approximately every 5 minutes after lens insertion with the modified slit lamp for one hour. Average intensity profiles were computed as a function of radial distance from the corneal center. Fluorescence intensity variations over time at different distances from the corneal center were modeled as an exponential function, from which we obtained the estimated fluorescence intensity decay rates. A multivariate regression was performed to assess the relationship between fluorescence decay rate and noninvasive tear break-up time (NITBUT) on the pre-lens surface, distance from the corneal center, lens type, central corneal curvature, corneoscleral junction (CSJ) profile, lens-fit characteristics, and corneal staining.
Fluorescence decay rate was significantly different across the three lens types (p<0.5): N&D had the highest decay rate while BIO had the lowest. Decay rate was greater with more vertical lens decentration, better wettability, tighter lens fit, shorter NITBUT, less corneal staining, and smoother CSJ. Decay rate was not related to corneal curvature nor was it related to the distance from corneal center after accounting for lens-fit parameters and ocular characteristics.
Different lenses demonstrated variations in fluorogram patterns and in their changes over time, suggesting differential post-lens tear mixing, which can also be influenced by CSJ profile, lens fit, and ocular health.
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