Tear evaporation in contact lens wear

Abstract

Abstract: : Purpose:The prevalence of dry eye complaints is significantly higher amongst contact lens wearers than for aged matched non wearers. Contact lens related dry eye is associated with a less stable tear film and a greater prevalence of conjunctival anomalies than amongst non wearers. The purpose of the investigation was therefore to measure tear film evaporation of contact lens wearers (with and without contact lenses) and of non wearers. The hypothesis tested was that tear evaporation during contact lens wear was significantly higher than for non wearers, but returned to normal upon contact lens removal. Methods:Tear evaporimetry was measured at 30% and 40% relative humidity and the severity of conjunctival damage was rated by lissamine green (LG) staining. The measurements for contact lens wearers (n=26 eyes) aged 34 ± 4.5 years both during contact lens wear and 10 to 30 minutes post removal were compared to a group of non wearers (n=34 eyes) aged 32 ± 6.4 years. Results:Evaporation during contact lens wear was significantly higher (p<0.01) than post contact lens wear, with a mean increase of 60.3% (17.4 vs. 10.5 10^–7 g/cm² /s) at 30% relative humidity and 60.4% (18.2 vs. 11.0 10^–7 g/cm² /s) at 40% relative humidity. Evaporation during contact lens wear was also higher (p<0.01) than for the non contact lens wearers with a mean difference of 57.5% (17.4 vs. 10.0 10^–7 g/cm² /s) at 30% humidity and 134.8% (18.2 vs. 7.4 10^–7 g/cm² /s) at 40% humidity. Within 30 minutes of contact lens removal evaporation was similar to that of non contact lens wearers at 30% humidity (p>0.05) but still significantly higher at 40% (p<0.01). Finally amongst contact lens wearers eyes with positive lissamine green staining (n=24) in the nasal quadrant had significantly higher (p<0.05) evaporation rates. Conclusions:The investigation confirmed that tear film evaporation was higher during contact lens wear than without contact lenses, and showed that evaporation returns rapidly to a normal level post contact lens removal. Furthermore, amongst contact lens wearers tear evaporation was significantly higher for the subjects with lissamine green staining, suggesting that dry eye anomalies in contact lens wear have a significant conjunctival component.

Keywords: cornea: tears/tear film/dry eye