Scleral Lens Thickness May Determine Central Corneal Edema in Open Eye Conditions

Thicker scleral lenses result in a higher magnitude of central corneal edema under open eye conditions, according to research published in Eye & Contact Lens.

Researchers enrolled 9 healthy adults (mean age 30 years, 4 women) in a study to assess a potential association between scleral lens thickness and central corneal edema under short-term, open eye conditions. The team randomly fit participants with scleral lenses with nominal central thicknesses of 150, 300, 600, and 1200 µm, and each participant wore lenses of each thickness 1 time. The investigators had the cohort wait a period of 24 hours following lens removal before fitting them with subsequent lenses. The researchers measured epithelial, stromal, and total corneal edema with high-resolution optical coherence tomography (OCT) at baseline and follow-up conducted 90 minutes following the insertion of each lens.

Researchers corrected for variations in initial fluid reservoir thickness across different lens thickness conditions, fitting a second order polynomial to each participant’s central corneal edema data as a function of fluid reservoir thickness measured under open-eye conditions. They examined the effect of lens center thickness on fluid reservoir characteristics and central corneal edema with one-way repeated measure analysis of variance’s (RM-ANOVA) and made Bonferroni corrections.

Investigators determined that total corneal edema was 1.14±0.22%, 1.36±0.26%, 1.74±0.30%, and 2.13±0.24% for the 150, 300, 600, and 1200 µm lenses, respectively. They also observed significantly more stromal and total corneal edema in the thickest lens (1200 µm) compared with the thinnest lens (150 µm)

“When controlling for scleral lens oxygen permeability and initial fluid reservoir thickness, increasing the lens thickness increases the extent of central corneal edema,” according to the researchers. “However, lens thickness values between 150 and 600 µm result in a similar level of edema (on average <0.6% variation). Theoretical models overestimate the effect of increasing scleral lens thickness upon central corneal edema for higher lens thickness values (i.e., when lens Dk/t is <20) when controlling for initial fluid reservoir thickness. In clinical practice, if a scleral lens with a Dk≥100 is used, a greater reduction in edema will be achieved by reducing the fluid reservoir thickness compared with an equal reduction in lens thickness (for thickness values of 600 mm or less).”

The researchers assert that modifying the fit of the landing zone to allow some ingress of oxygenated tears into the fluid reservoir may increase oxygen transmission and reduce corneal hypoxia. However, it may also result in fluid reservoir debris.

Study limitations include a small sample size, short study duration, and variations in initial central flow reservoir thicknesses among the different lenses.

Reference

Fisher D, Collins MJ, Vincent SJ. Scleral lens thickness and corneal edema under open eye conditions. Eye Cont Lens. 2022;48(5):200-205. doi:10.1097/ICL.0000000000000888