Comparison of tear-film osmolarity in different types of contact lenses.

Abstract

To investigate the tear-film osmolarity of contact lens wearers for different types of contact lenses. Fifty six eyes of 56 cases were evaluated in four different groups according to the type of contact lens worn, with 14 eyes in each group. Groups 1 and 2 consisted of subjects who wore frequent-replacement daily wear soft contact lenses; group 1 lenses had 55% water content, and lenses in group 2 had 38% water content. Groups 3 and 4 consisted of subjects who wore rigid gas-permeable contact lenses, with a Dk value of 90 in group 3 and a Dk value of 52 in group 4. Tear-film osmolarity values in milliosmole (mosm) units were determined by auto-osmometer (Orstat 6030, Daiichi Kagacu, Kyoto, Japan) before and after contact lens wear for each group, and the results were compared statistically by ANOVA test. Before the period of contact lens wear, the tear-film osmolarity values of group 1, 2, 3, and 4 were 283.61+/-12.83 mosm, 285.23+/-8.94 mosm, 285.57+/-11.39 mosm, and 280.15+/-12.07 mosm, respectively. After the period of contact lens wear, these values were measured at 312.15+/-16.03 mosm in group 1, 316.54+/-12.14 mosm in group 2, 313.14+/-9.66 mosm in group 3, and 316.38+/-11.60 mosm in group 4. Although the difference between the values before and after the period of contact lens wear was statistically significant for each group (F=291.45; P=0.0005), there was no statistically significant difference among the groups. When a contact lens is placed in the eye, the lens alters the normal structure of the tear film and affects its rate of evaporation; therefore tear-film osmolarity may increase. In our study, all contact lenses produced a similar effect on tear-film osmolarity.