Lens thickness does not appear to affect corneal edema in patients wearing scleral contact lenses, according to research published in Eye & Contact Lens.
Scleral lenses tend to deliver less oxygen to the cornea compared with thinner lens types. The study objective was to examine how altering central scleral lens thickness affects corneal edema under short-term, closed eye conditions.
Researchers fitted 9 healthy adults (mean age 30 years, 4 women) with scleral lenses (Dk 141) and established a targeted initial central fluid reservoir thickness of 500 µm. The team randomly assigned participants to central lens thicknesses of 150, 300, 600, and 1200 µm on separate days and had participants wait a total of 24 hours before fitting them with the next lens. They measured corneal thickness and central fluid reservoir thickness via optical coherence tomography (OCT) after lens insertion. The investigators patched the eye with the scleral lens while the fellow eye remained open and had participants engage in near work for 90 minutes. Researchers then repeated OCT measurements. They corrected total corneal edema data to control for fluid reservoir thickness’ impact on magnitude of corneal edema.
The team observed a significant variation in initial (P =.004) and final (P =.001) central fluid reservoir thickness with lens thickness change. Corrected total corneal edema was 4.31%±0.32%, 4.55%±0.42%, 4.92%±0.50%, and 4.83%±22% for the 150, 300, 600, and 1200 µm lenses, respectively. Central corneal edema did not vary significantly for raw or corrected total thickness data.
“When controlling for scleral lens oxygen permeability and initial fluid reservoir thickness, under short-term closed eye conditions, increasing scleral lens thickness did not significantly increase central corneal edema (a mean increase of 0.52% when increasing center thickness from 150 to 1,200 mm),” according to the researchers. “Theoretical modeling seems to overestimate the effect of increasing scleral lens thickness on central corneal edema for higher lens thickness values (i.e., when the lens Dk/t reduces to approximately 25). Minimizing central fluid reservoir thickness provides a greater reduction in corneal edema compared with the decrease in lens thickness under short-term closed eye conditions.”
The researchers suggest clinicians be aware that scleral lenses fit with minimal clearance may be difficult to remove because of suction, particularly following closed eye wear. They discourage using scleral lenses as overnight therapeutic bandage lenses, but affirm their use for patients with advanced corneal disease.
Study limitations include a small sample size, short study duration, and variations in initial central flow reservoir thicknesses among the different lenses.
Fisher D, Collins MJ, Vincent SJ. Scleral lens thickness and corneal edema under closed eye conditions. Eye Cont Lens. 2022;48(5):194-199. doi:10.1097/ICL.0000000000000852