Dehydration of hydrogen contact lenses in vitro and in vivo

An attempt was made to derive a model for predicting the extent of hydrogel lens dehydration in vivo (delta Wv) by using a contact lens refractometer to (1) measure the water content (W) of eight lenses ranging from 36.5 to 85.8% water before and after 90 min lens wear by six subjects; and (2) measure the rate of dehydration of the same lenses in vitro (delta Wt), in a controlled, randomized, double-masked experiment. A significant correlation was demonstrated between W and the rate of change of delta Wt (the dehydration rate, D), whereby lenses of higher water content dehydrate at a slower rate. No correlation was found between W and delta Wv or between D and delta Wv, thus precluding the development of a predictive model. Possible reasons for this failure, and directions for further research, are discussed.