Abstract
Purpose :
The dynamics of water transport through hydrogel contact lenses and water loss from the ocular system leading to contact lens induced dry eye (CLIDE) are not well understood. Evaporative loss in which water evaporates directly from the lens occurs when the tear film breaks exposing the polymeric surface to air. The material dependent rates of water permeation and evaporation have been measured for a wide range of lens materials. A simple model that considers these water transport rates along with polymer-air exposure time can be used to estimate the evaporative water loss from the eye.
Methods :
Evaporation rates (n=6 per material) were determined using a newly designed pervaporation cell mounted inside a dynamic vapor sorption instrument. This system provides complete control over the temperature and humidity of the environment. Evaporation rates were measured at 80%, 50%, 30%, and 0% relative humidity. These rates, along with values for the area of exposed lens polymer and exposure time between blinks, were used to create a model for evaporative loss from the lens polymer during periods of tear film break up.
Results :
Under conditions of high (80%) relative humidity all lens materials have a low evaporation rate with a value of approximately 0.2 µL/min/cm2. At low humidity (0 - 30%) the evaporation rate increases, and a large material dependence is evident with rates ranging from 0.3 up to 1.4 µL/min/cm2. Silicone hydrogel materials with strong hydrophiles exhibit a high degree of resistance to evaporative water loss. Modeling shows that evaporative water loss from the lens polymer during periods of tear film break up could be as high as 0.5 µL/min.
Conclusions :
These results imply that the water in the tear film is in rapid equilibrium with water in the contact lens and that evaporative loss from the surface of the lens is rapidly replenished by water from the bulk of the lens and ultimately from the tear film. Resistance to evaporative loss from the lens polymer during tear film break up may be an important factor in understanding CLIDE.
This is a 2020 ARVO Annual Meeting abstract.