Researchers recently investigated the potential hypoxic effects of scleral lens wear and found the lenses cause corneal edema that’s stromal in nature and is significantly affected by the thickness of the fluid reservoir. The team came to this conclusion by comparing theoretical and empirical measurements of scleral lens-induced corneal edema with respect to the fluid reservoir thickness. They examined this potential effect during short-term open-eye scleral lens wear in 10 participants with normal corneas and highly oxygen-permeable scleral lenses.

Patients wore the lenses on separate days with either a low, medium or high initial fluid reservoir thickness. The researchers measured epithelial, stromal and total corneal edema using OCT after 90 minutes of wear but before lens removal and then compared their measurements with published theoretical models of scleral lens-induced corneal edema.

The mean total corneal edema was 0.69%, 1.81% and 2.11% for low, medium and high thickness reservoir groups. They found no significant difference in corneal edema between the medium and high fluid reservoir groups. For fluid reservoir thickness values greater than 400μm, they found the theoretical models overestimated corneal edema.

Although scleral lens-induced corneal edema increases with fluid reservoir thickness, it “plateaus around a thickness of 600μm in agreement with recent theoretical modeling that incorporates factors related to corneal metabolism,” the researchers wrote in their paper.

Fisher D, Collins MJ, Vincent SJ. Fluid reservoir thickness and corneal edema during open-eye scleral lens wear. Optom Vis Sci. 2020;97:9:683-9.