Change In Tear Layer Thickness Under Scleral Contact Lenses In Keratoconus Patients And Normal Cornea Volunteers

To quantify the rate of post-lens tear thickness change under scleral contact lenses in keratoconus patients and normal cornea volunteers.

A prospective observational study was conducted at the Department of Ophthalmology, Siriraj Hospital, from January 2022 to May 2023.

This prospective observational study was conducted at the Department of Ophthalmology, Siriraj Hospital, from January 2022 to May 2023. Semi-scleral lenses were fitted to 20 eyes (10 eyes in each keratoconus and normal cornea group, as indicated by corneal topography). All subjects were fitted with a semi-scleral lens designs Onefit SC® diameter 14.7 mm. After insertion, post-lens tear thickness was measured using Anterior Segment OCT (CASIA2) at 8 time points: 0 minutes, 30 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours following lens insertion. Linear mixed model was employed to compare post-lens tear thickness and rate of thickness change at each time point within and between groups.

Mean initial post-lens tear thickness (µm) was 740 ± 51 and 441 ± 51 in keratoconus and normal cornea group, respectively. Mean rate of change (µm/hr) was greatest in the first 30 minutes in both groups (77.7 ± 5.7 in keratoconus group and 135.8 ± 5.7 in normal cornea group). The rate of reduction of post-lens tear thickness after 2 hours (in keratoconus group) and after 1 hour (in normal cornea group) exhibit no statistically significant difference from the rate of change during the 5-6 hour period. Mean percentage of total change in 6 hours after lens insertion was higher in normal cornea group than in keratoconus group (36.3% vs 22.4%). 

The amount and rate of post-lens tear change beneath a scleral lens varies among different corneal conditions. The reduction in post-lens tear thickness demonstrates a non-linear trend. Mean rate of change was greatest shortly after insertion and only slightly changed after 2 hours in keratoconus and 1 hour in normal cornea following lens insertion. The percent change was greater in normal cornea group than in keratoconus group.