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DE Hart, S Martin, BD Ratner; Determination of Lens Type Using a Cationic Dye . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3094.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: This study aims to find a classification based upon the interaction of lenses with lysozyme binding sites using methylene blue, a cationic dye. Currently lenses are grouped by empirical formula. Methods:Methods: 3 samples each of 12 different contact lenses were soaked for 2 hours in 5 ml of 0.02% methylene blue. Lenses were removed, placed in dishes containing 20 ml of double distilled water. Intensity of blue color for a lens was recorded. The dishes gently shaken overnight and color was rerecorded. 1 ml from each of the washings were measured at 665 nm. Results: Hierarchical cluster analysis was used to quantitatively categorize lenses according to observations of lens, solution appearance and absorption. The cluster analysis depicts a dendrogram. Quantifying the number of clusters determined is provided by scree analysis, indicating 3 distinct clusters. Kruskal-Wallis one-way analyses of variance compares the clusters for each observation of dye adherence. The nonparametric method was was because the observations weren't distributed normally. Based on results of ANOVAs it is clear that clusters represent three distinct patterns in dye adherence to the lens; with cluster 1 containing most adherent lenses and cluster 3 least adherent lenses. Lenses in cluster 2 fall between the two extremes. These differences are apparent after initial wash (H=21.5, df=2, P<.0001, Dunn's Method of post hoc pairwise comparisons, P<.05) in which lenses in clusters 1 and 2 are significantly darker and wash solutions lighter compared to lenses in cluster 3. Cluster 1 lenses continue to hold dye after a second wash (next day) compared to cluster 3. In contrast, results for cluster 2 lenses fall between those for cluster 1 & 3 (Lens / Solution Condition: Next Day Wash, H=20.4, df=2, P<.001, Dunn's Method of post hoc pairwise comparisons, P<.05) or are not significantly different from results for cluster 3 (Lens Condition: Next Day Wash, H=25.5, df=2, P<.001; Solution Absorbance: Next Day Wash, H=19.9, df=2, P<.001, Dunn's Method of post hoc pairwise comparisons, P<.05). There were no differences in water content between clusters (Kruskal-Wallis one-way analysis of variance, H=1.2, df=2, P=0.527). FDA groupings are imperfect predictors of a lens in a given cluster Conclusion: We are currently comparing affinity of lysozyme and methylene blue for lenses. The affinity of a cationic dye for a lens describes its ionic nature better than the chemical formula-based FDA classification.
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