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Previous studies have shown that soft lenses dehydrate during lens wear. The purpose of this study was to determine the dehydration time course of 38% water content non-ionic Medalist, 58% ionic Acuvue and 74% non-ionic Permaflex lenses, and the relationship between dehydration and in vivo diameter, movement and symptoms of dryness. Nineteen subjects randomly wore three pairs of lenses, each for 7 h. Lens movement and diameter were measured in vivo and hydration after lens removal at 1, 3 and 7 h. Dryness was rated by the subjects using a visual analogue scale. A separate experiment was conducted to measure hydration changes after 7 continuous hours of lens wear. The water content of all three lens types decreased significantly over 7 h with Acuvue decreasing more than the Permaflex and Medalist lenses in the interrupted and continuous experiments (ANOVA P < 0.05). Dehydration of Acuvue was significantly greater in the 7 h continuous experiment (9.0 +/- 2.6% H2O, ANOVA P = 0.0062) compared to the interrupted experiment. Hydration levels measured for Acuvue lenses on subjects for control purposes at 0, 1, 3 and 7 h showed no difference over time (ANOVA P = 0.0711). Movement of Permaflex lenses decreased 0.60 +/- 0.57 mm (ANOVA P = 0.0005) over 7 h and the in vivo diameter of Acuvue lenses decreased by 0.12 +/- 0.16 mm (ANOVA P = 0.0569). Dryness ratings increased significantly and equally for all three lenses over 7 h (ANOVA P = 0.9833).(ABSTRACT TRUNCATED AT 250 WORDS)

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