REGIONAL VARIATION IN FLUID RESERVOIR THICKNESS, OXYGEN TRANSMISSIBILITY AND CORNEAL OEDEMA DURING SCLERAL LENS WEAR

Abstract

Purpose: To determine if regional variation in post lens fluid reservoir thickness (PLFT) during scleral lens wear leads to regional variation in oxygen transmissibility and corneal edema during 4 hours of non-
fenestrated scleral lens wear.
Methods: About 20 healthy subjects (mean age, 28.8 ± 4.2 years) were fitted with nonfenestrated rotationally symmetric scleral lenses. Anterior segment optical coherence tomography was used to measure cornea thickness before and after lens wear, PLFT 10 minutes and 4 hours after lens application, and scleral lens thickness (with the scleral lens in situ) 4 hours after scleral lens application. These measurements were limited to the central 6 mm and divided into three zones (central, mid-peripheral, and peripheral zones). In the mid-peripheral and peripheral zones, eight principal meridians were measured, generating 17 measurement points in total. Scleral lens thickness and PLFT measurements were corrected for optical distortions by a series of equations. Oxygen transmissibility was calculated by dividing the scleral lens oxygen permeability by the optically-corrected scleral lens thickness, taking into account the oxygen permeability of saline and fluid reservoir thickness.
Results: A significant regional variation in PLFT (F = 12.860, P = 0. 012) was observed after 10 minutes of the lens application, PLFT was thickest and thinnest in the inferotemporal and the superonasal region of the peripheral zones( 322.6 ± 161.8 µm and 153.8 ± 96.4 µm, respectively); however, this variation was not statistically significant at 4 hours of scleral lens wear (F = 4.692; P = 0.073). Despite significant regional variation in oxygen transmissibility (F = 48.472; P = 0.001) and relatively low oxygen transmissibility through the scleral lens, induced corneal edema did not vary significantly in different regions (F = 3.346; P = 0.126). In the central corneal region, the induced corneal edema correlated moderately with PLFT (r = 0.468; P = 0.037) and oxygen transmissibility (r = -0.528; P = 0.017). This relationship was insignificant in the peripheral cornea.
Conclusion: The inferotemporal peripheral region had the thickest PLFT and least oxygen transmissibility, and the superonasal region had the vice versa. Despite significant variation in PLFT and oxygen transmissibility initially, in healthy corneas, this variation does not seem to induce statistically significant regional variation in corneal edema. Increased central PLFT and decreased oxygen transmissibility moderately correlate with central corneal edema.