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Ian G. Cox, Rosa H. Lee; Understanding Lens Shape Dynamics During Off-Eye Dehydration of Contact Lens Materials with Varying Water Content. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6104.
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To understand the lens shape dynamics during off-eye dehydration for a novel lens material and 3 commercially available daily disposable contact lenses.
Four -3.00D lenses of each lens (type, water content) (etafilcon A [AV Moist], 43%; narafilcon B, 48%; nelfilcon A, 69%; investigational lens, 78%) were tested. Each lens was taken out of the package and blotted to remove excess packaging solution. All 16 lenses were allowed to dehydrate under the same ambient conditions of approximately 72°F with a RH of 30%. A photo was taken every 2 minutes over the 20min period. Four pairs of photos for each lens type (time 0 and time 20mins) were presented to 12 random subjects who rated whether the lens shape of image A compared to image B was similar or different, using a 10 point rating scale where 1 corresponded to "Extremely Similar" and 10 corresponded to "Extremely Different".
Shape changes occurred throughout the 20 minute period. All 3 commercially available contact lens materials showed significant edge "fluting" as a result of lens dehydration at the end of the 20 minute test period, while the investigational contact lens material did not. A one-way ANOVA showed a statistically significant difference (p<0.0001) between the investigational lens (A) compared to nelfilcon A (D), narafilcon B (C) and etafilcon A (B), where the mean rating scores were 1.9, 8.8, 8.4, 6.8, respectively.
Traditional clinical literation and belief suggests that higher water content lenses dehydrate more than lower water content lenses. In this study, the novel lens material demonstrated a more consistent lens shape over the 20 minute dehydration period compared to narafilcon B, 48%; nelficon A, 69%; and etafilcon A, 43% lenses, suggesting that the investigational material has unique properties relative to water retention. Further research is needed to understand the impact of dehydration driven lens shape change on vision, comfort and fitting performance in-vivo.
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