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Haixia Liu, Carolyn G. Begley, Trefford Simpson, Jun Zhang, Meredith E. Jansen, Nikole Himebaugh, Ziwei Wu, Pete S. Kollbaum; Non-invasive High Resolution Imaging And Objective Quantification Of Contact Lens Wettability. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6475.
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The purpose of this study was to develop a non-invasive, in vivo, high resolution, objectively quantifiable method of SCL wettability assessment using a standard slit lamp biomicroscope with minor alterations that could be employed in clinical practice or clinical trial settings.
A slit-lamp microscope was modified to emit only infrared illumination (to maximize the pupil size), the tear film over the SCL was imaged using a combination of specular reflection (SR) and retroillumination (RI) and was videotaped using a Point-grey (Point Grey Research, Richmond, BC, Ca) high resolution camera. The system was tested on 10 SCL wearing subjects who kept one eye open as long as possible while real time contrast sensitivity (CS) was simultaneously measured through a beam splitter. Four frames from each trial (spaced equally across the time of data capture) were selected and graded using the Contact Lens Evaluation of Wettability (CLEW) scale. Two quantitative SCL wettability analyses, tear break-up edge pixels (EP) and Purkinje size (PS) were calculated with custom MATLAB programs.
The technique provided high resolution dynamic imaging of tear break-up over the SCL within the pupil. Changes in CLEW grades were significantly correlated with EP and CS (r=0.74, 0.64, Spearman’s rho, p<0.05), but not with PS (r=0.053). The relative changes in EP within each trial increased with CLEW grade (AVG±SD); Grade 1 (571±420), Grade 2 (1063±492), Grade 3 (1369±295), Grade 4 (3034±165), with significant differences in EP between all grades except 2 and 3; the relative change in CS increased with CLEW grade (AVG±SD); Grade 1 (0.19±0.17), Grade 2 (0.42±0.32), Grade 3 (0.31±0.39), Grade 4 (0.93±0.02), with significant differences between grade 4 and others (p<0.05, ANOVA with Bonferroni post hoc).
This novel imaging technique provides high resolution, objectively quantifiable images of SCL wettability over the pupil that show a high correlation with visual function (CS). The method involves minor modification of a standard slit lamp biomicroscope and thus can be easily adapted and developed for a non-invasive assessment of the SCL or corneal surface in a clinical trial setting.
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