A comparative study of tear evaporation rates and water content of soft contact lenses.

Tear evaporation rates were measured by resistance hygrometry in a group of five subjects wearing soft contact lenses ranging in initial water content from 38 to 70%. The water content of the lenses before and after wear was measured by a "wet blot weighing" technique using a chemical balance. The placing of all types of soft lenses on the eye disrupts the tear film sufficiently to produce significant increases in evaporation. This increase in tear evaporation was not found to be related to the initial water content of the soft lens. Water lost by dehydration of the lens material made a relatively minor contribution to the increase in evaporation from the eye during lens wear.