Hydrogel contact lens dehydration rates determined by thermogravimetric analysis

Because many practitioners believe that the on-eye drying of contact lenses is a source of patient discomfort, we examined the relative dehydration rates of a variety of hydrogel contact lenses. Lens dehydration rates were determined by thermogravimetric analysis at 35[degrees]C. Using the FDA classification scheme for hydrogel lenses, we found that dehydration rates were as follows: group 4 greater than group 2 greater than group 3 greater than group 1. Within groups there was considerable variability in the rates at which lenses dehydrated. For lenses of the same type, we found a near-linear relationship between increasing lens power (which is closely related to center thickness) and decreasing rates of dehydration.