Characterization of the Pre-lens Tear Film in Hydrogel and Silicone Hydrogel Contact Lens Wear.

Purpose: Different contact lens (CL) materials have been associated with different behaviors of pre-lens tear film components in the short term. The purpose of this randomized crossover and double-masked study was to compare the effect of wearing hydrogel and silicone hydrogel CLs on pre-lens tear film status.

Methods: Soft CL wearers were recruited and randomly fitted with a hydrogel (omafilcon A) and a silicone hydrogel (stenfilcon A) CL. Tear evaporation rate, non-invasive tear break-up time (NIBUT), tear film lipid layer thickness, and partial blink rate were measured without CLs and 30 minutes after the insertion of CLs. The outcomes were analyzed using repeated measures analysis of variance or the Friedman test.

Results: Twenty-four CL wearers (6 men and 18 women) aged 23.3 $\pm$ 3.9 years were included. Tear evaporation rate was higher with the hydrogel CL (98.6 $\pm$ 59.4 g/m²/h; P = 0.043) and the silicone hydrogel CL (99.7 $\pm$ 60.6 g/m²/h; P = 0.037) compared to no CL wear (69.9 $\pm$ 41.3 g/m²/h). NIBUT was lower (P = 0.019) with the silicone hydrogel CL (12.7 $\pm$ 6.2 s) than with no CL wear (18.5 $\pm$ 9.8 s). Lipid layer thickness was lower with the hydrogel CL (64.9 $\pm$ 15.5) than with the silicone hydrogel CL (75.8 $\pm$ 14.0; P $<$ 0.001) and no CL wear (75.9 $\pm$ 14.2; P = 0.001). No statistically significant differences were found in the partial blink rate.

Conclusion: This study demonstrated that both hydrogel and silicone hydrogel CLs disrupt the tear film by increasing tear evaporation and causing tear film instability. However, CL materials affect the pre-lens tear film status differently. Further studies with longer wearing times are required.