The aim of the study was to measure tear film evaporation of both contact lens wearers (CLW) and nonwearers. The hypotheses tested were that (i) amongst CLW tear film evaporation was higher when contact lenses are worn and (ii) tear film evaporation of CLW was higher than nonwearers in the absence of contact lenses.
Tear film evaporation rate was measured at 30% and 40% mean humidity. The subjects were divided into 3 groups: (i) CLW wearing contact lenses (n = 111 subjects or 222 eyes), (ii) CLW having not worn contact lenses on the day of the visit (CLW no CL n = 129 subjects or 258 eyes), and (iii) Non-contact lens wearers (NW) (n = 139 subjects or 278 eyes).
The rate of evaporation was similar for the right and left eyes at both humidities. The rate of evaporation was significantly higher for the CLW, than for both CLW no CL and NW. The decrease in the rate of evaporation between the dry (30%) and normal (40%) environmental conditions was significantly lower for the CLW than for the NW. Further, the evaporation rate was significantly greater for the CLW, even after 1 day without contact lens wear, than for the nonwearers.
The investigation demonstrates that the rate of evaporation is higher in the presence of a contact lens; the effect may be associated with tissue and/or tear film changes as it is, in part, still present 24 hours after contact lens wear. Wearing contact lenses in normal humidity conditions (40%) produces a greater evaporation than that experienced by non-contact lens wearers in low humidity (30%). This could explain the higher prevalence of dry eye complaints among CLW than amongst nonwearers. The study results support the hypothesis of increased evaporation as a contributing factor to contact lens induced dry eyes.