Effect of environmental conditions on tear dynamics in soft contact lens wearers

Dry eye symptoms are often associated with soft contact lens (SCL) wear and may be affected by environmental conditions. This study was conducted to determine the effects of temperature and humidity on the tear film in SCL wearers.

All 11 enrolled subjects were males (mean age, 23.5 +/- 5.2 [SD] years), and all wore SCL daily. They were exposed in different sessions to four different conditions in an environmental chamber with the air temperature (AT) and relative humidity (RH) set at 5 degrees C/10% (AT/RH), 15 degrees C/20%, 25 degrees C/40%, or 35 degrees C/50%. Two different types of hydrogel SCL (SCL-a and SCL-b; water content 72.0% and 37.5%, respectively) were used. The meniscus tear volume was determined on a video meniscometer by measuring the tear meniscus radius (TMR) with and without SCL. The tear interference patterns on the contact lens (TIPCL) were classified into five grades (the higher the grade, the thinner the film). Using a video interferometer, the non-invasive tear film breakup time (NIBUT) was recorded with and without SCLs; ocular dryness was also scored with and without SCLs.

Under the environmental conditions examined, there were no significant differences in the TMR without or with SCL, regardless of their type. As AT and RH decreased, there was a significant increase in the TIPCL grade (CL-a: P = 0.042; CL-b: P = 0.002), a significant decrease in NIBUT (CL-a: P = 0.004; CL-b: P = 0.001), and a significant increase in the dryness score (without SCL P = 0.023; with CL-a P = 0.009; with CL-b P = 0.003). The dryness scores were higher with CL-a than CL-b (P = 0.011 at 15 degrees C/20%). Under identical experimental conditions, we observed no significant change in NIBUT in the absence of an SCL.

AT and RH apparently had no effect on the tear volume in the presence of SCLs. As AT and RH decreased, the tear film on the SCL became thinner, NIBUT became shorter, and dryness increased. Dryness was more pronounced in eyes with SCL of the higher water content.