Fluid Reservoir Thickness and Corneal Edema during Open-eye Scleral Lens Wear

Abstract

SIGNIFICANCE There is debate concerning corneal oxygenation during scleral lens wear due to the potential additive hypoxic effect of a lens plus a fluid reservoir. This study investigated the agreement between theoretical models and empirical measurements of scleral lens–induced corneal edema with respect to central fluid reservoir thickness. PURPOSE The purpose of this study was to examine the effect of altering the fluid reservoir thickness on central corneal edema during short-term open-eye scleral lens wear and to compare these empirical measurements with predictive theoretical models. METHODS Ten participants (age, 30 ± 4 years) with normal corneas wore highly oxygen-permeable scleral lenses (141 Dk ×10−11 cm3 O2 (cm)/[(s) (cm2) (mmHg)]) on separate days with either a low (mean, 144; 95% confidence interval [CI], 127 to 160 μm), medium (mean, 487; 95% CI, 443 to 532 μm), or high (mean, 726; 95% CI, 687 to 766 μm) initial fluid reservoir thickness. Epithelial, stromal, and total corneal edema were measured using high-resolution optical coherence tomography after 90 minutes of wear, before lens removal. Data were calculated or extracted from published theoretical models of scleral lens–induced corneal edema for comparison. RESULTS Scleral lens–induced central corneal edema was stromal in nature and increased with increasing fluid reservoir thickness; mean total corneal edema was 0.69% (95% CI, 0.34 to 1.04%), 1.81% (95% CI, 1.22 to 2.40%), and 2.11% (95% CI, 1.58 to 2.65%) for the low, medium, and high thickness groups, respectively. No significant difference in corneal edema was observed between the medium and high fluid reservoir thickness groups (P = .37). “Resistance in series” oxygen modeling overestimated the corneal edema observed for fluid reservoir thickness values greater than 400 μm. CONCLUSIONS Scleral lens–induced central corneal edema increases with increasing reservoir thickness, but plateaus at a thickness of around 600 μm, in agreement with recent theoretical modeling that incorporates factors related to corneal metabolism.

Central-to-peripheral corneal edema during wear of embedded-component contact lenses

“…With ESL assessment, settled PoLTF thicknesses greater than 400 μm were not investigated because Kim et al [22] calculated that thicknesses greater than 400 μm permit buoyancy-driven fluid convection that dominates oxygen mixing compared to molecular diffusion. Therefore, model prediction is accurate up to thicknesses of about 400 μm [22] beyond which a diminishing effect of PoLTF thickness on central corneal edema is expected and in agreement with Fisher et al [48]. Because heat generated by battery-powered embedments may affect buoyancy-driven fluid convection, investigation of PoLTF-temperature profiles is warranted with ESL wear.…”

Fluid reservoir thickness and aberration relationship in keratoconic eyes with scleral lenses

“…Considering this range, the present study reported an excessive amount of FR thickness in high FR lenses, and although this did not affect HOAs, it might have a negative impact on normal corneal physiology and thus should be avoided. Fisher et al 42 . reported a smaller amount (2%) of corneal oedema after short‐term wear of a SL with a central FR thickness up to 700 microns.…”

BCLA CLEAR - Effect of contact lens materials and designs on the anatomy and physiology of the eye

“…This is supported by evidence that corneal neural structures are unchanged with scleral lens wear [366,373]. However, scleral lens materials with an insufficient Dk [374], or with an excessive post-lens tear reservoir [127,128] will produce oedema, suggesting that either scenario may produce a reduced sensitivity.…”

“…Post-lens hypoxia is treated by choosing a lens material with a higher Dk [125,126]. Hypoxia is still an issue for scleral/overnight medical wear due to the effect of the post-lens fluid reservoir [127,128]. • A less stable tear film can be produced in contact lens wear, which induces increased tear evaporation [129][130][131], leading to partial dehydration of the lens material [132,133].…”