Absorption of ammonia by high water content hydrogel lenses: an inexpensive method of analysis

Few studies have been done on the absorption and release of chemical vapors by high water content hydrogel lenses. In this study we investigated the absorption of ammonia vapors by this type of contact lens (CL). Ten high water content hydrogel lenses were exposed to vapor generated in a cuvette by 1 drop of aqueous ammonia. The contact lens was transferred to a 0.9% saline solution containing a colorometric indicator for ammonia and the amount of ammonia released into the saline was measured. We found that significant quantities of ammonia were absorbed into the lenses and the relation between average concentration of ammonia vapor and amount absorbed per contact lens was nearly linear from 50 parts per million (ppm) to 250 ppm ammonia vapor. For concentrations greater than 250 ppm there appears to be a saturation effect. Our findings indicate that high water contact lenses will absorb ammonia and release it into a solution similar to tears.