Change in Tear Layer Thickness under Scleral Contact Lenses in Keratoconus Patients and Normal Cornea Volunteers

Objective: To quantify rate of post-lens tear thickness change under scleral contact lenses in keratoconus patients and normal cornea volunteers. Materials and Methods: We conducted a prospective observational study where semi-scleral lenses were fitted to 20 eyes (5 subjects, 10 eyes in each group). After insertion, post-lens tear thickness was measured at 0, 30 minutes and every hour up to 6 hours using Anterior Segment OCT. To analyze post-lens tear thickness and its rate of change at each time point, both within and between groups, a linear mixed model was used. Results: The initial mean post-lens tear thickness (µm) was 742 ± 50 and 440 ± 50 in keratoconus and normal cornea group, respectively. The mean rate of change (µm/hr) was highest in the first 30 minutes in both groups (80.8 ± 8.7, 132.2 ± 8.8 in keratoconus and normal cornea group). Following the first four hours in keratoconus and the first hour in normal cornea group, the reduction rate in post-lens tear thickness exhibited no statistically significant difference from the rate of change observed during the 5-6 hour period. The mean percentage of total change over 6 hours after lens insertion was higher in normal cornea compared to keratoconus group (36.6% vs 22.5%). Conclusion: The reduction in post-lens tear thickness follows a nonlinear pattern. The mean rate of change was highest after insertion and remained stable after four hours in keratoconus and one hour in normal cornea group. The percent change over the 6-hour period was greater in normal cornea group.