Investigation of posterior corneal curvature in CL-induced corneal swelling

Abstract 

Purpose

To evaluate Orbscan II measurements without contact lens (CL) removal to monitor in vivo posterior corneal curvature in CL (hypoxia)-induced corneal swelling during extended wear (EW).

Methods

Orbscan II corneal topographer was used to measure posterior corneal curvature 1 week before CL wearing and during 1 week of EW. Central corneal thickness (CCT) was also measured during the 2-week study with OCT to determine the corneal swelling percentage. High Dk (lotrafilcon A) and low Dk (etafilcon A) soft CL were randomly fitted in EW in the right and left eyes of 20 subjects with normal ocular health. Orbscan and OCT were also performed without CL removal after 3 and 7 days of wear.

Results

Low Dk lenses induced significantly higher corneal swelling (2.41±2.65%), as compared to the high Dk lenses (0.17±2.28%; P<0.05 repeated measures ANOVA (Re-ANOVA and paired t-test) measures with OCT. The low Dk lens induced a significantly posterior corneal flattening compared to the high Dk lens (0.036±0.06mm versus 0.006±0.04mm; P<0.05 Re-ANOVA and paired t-test). High repeatability for Orbscan-measured posterior best fit sphere (BFS) radii with (r²=0.15, 95% limits of agreement (LoA)=0.10 to −0.06) and without (r²=0.00, 95% LoA=0.08 to −0.08) CL removal was also observed and suggest that posterior corneal changes was not due to Orbscan variability.

Conclusions

Orbscan is a non-invasive and reproducible technique to evaluate and monitoring posterior corneal curvature in vivo in CL (hypoxia)-induced corneal swelling during EW.

Keywords: Orbscan, Posterior corneal curvature, Corneal edema, Extended wear of contact lenses