Scleral Lens Thickness and Corneal Edema Under Closed Eye Conditions

Abstract

Objectives:To examine the relationship between central lens thickness and central corneal edema during short-term closed eye scleral lens wear.Methods:Nine participants (mean age 30 years) with normal corneas wore scleral lenses (Dk 141) under closed eye conditions on separate days with nominal center thicknesses of 150, 300, 600, and 1,200 μm. Epithelial, stromal, and total corneal edema were measured using high-resolution optical coherence tomography immediately after lens application and after 90 min of wear, before lens removal. Data were corrected for variations in initial fluid reservoir thickness and compared with predictions from theoretical modeling of overnight scleral lens wear.Results:Scleral lens–induced central corneal edema was primarily stromal in nature. The mean±standard error of corrected total corneal edema was 4.31%±0.32%, 4.55%±0.42%, 4.92%±0.50%, and 4.83%±0.22% for the 150-, 300-, 600-, and 1,200-μm lenses, respectively. No significant differences in the corrected total corneal edema were observed across all thickness groups (P=0.20). Theoretical modeling of overnight scleral lens wear seemed to overestimate the relative increase in central corneal edema as a function of decreasing lens Dk/t for values lower than 25.Conclusion:The magnitude of scleral lens–induced central corneal edema during short-term closed eye lens wear did not vary significantly with increasing central lens thickness. Theoretical modeling of overnight closed eye scleral lens wear seems to overestimate the effect of increasing lens thickness.

Corneal oedema during reverse piggyback scleral lens wear

“…11 This approach has been used previously to provide an estimated corrected value for corneal oedema. 24,25 Both the raw data and corrected data are presented in the results. Data were analysed using SPSS statistical software version 27.0 (IBM, ibm.com).…”

“…To provide an approximate correction for any small differences in the initial central fluid reservoir thickness between the scleral lens and reverse piggyback conditions, which has the potential to impact corneal oedema, 11 a correction factor was calculated for each participant using published data which quantified the variation in corneal oedema in young healthy eyes as a function of central fluid reservoir thickness 11 . This approach has been used previously to provide an estimated corrected value for corneal oedema 24,25 . Both the raw data and corrected data are presented in the results.…”

Scleral Lens Thickness and Corneal Edema Under Open Eye Conditions

“…All participants had completed a previous study examining the effect of scleral lens thickness on central corneal edema under closed eye conditions. 14 This experiment followed the same experimental procedures outlined previously; 14 however, both eyes remained open during the 90-min period of unilateral scleral lens wear. This period of lens wear was chosen because corneal edema peaks and stabilizes after 90 min of open-eye high-Dk modern scleral lens wear in healthy adults.…”

“…The order of lens wear (150, 300, 600 and 1,200 mm nominal lens center thickness) was randomized across the study visits, and the four measurement sessions were conducted at the same time of day for each participant to minimize the potential confounding influence of natural diurnal variations in corneal thickness. 18 After the same experienced contact lens practitioner applied the appropriate scleral lens with preservative-free saline (in the left eye only), corneal thickness (across the central 5 mm), and central fluid reservoir thickness (at the tangent to the normal of the corneal apex) were measured using the OCT and again after 90 min of lens wear, before lens removal, using the experimental protocol and analysis technique outlined previously by Fisher et al 13,14 All OCT images were analyzed by a single experienced observer following automatic segmentation. This technique is highly repeatable with a mean intrasession repeatability of less than 1 mm for measures of total corneal thickness (when averaging 3 OCT line scans).…”

“…Because of small differences in the initial fluid reservoir thickness across the different lens thickness conditions, a series of corrections were applied to each individuals' total corneal edema data, because the fluid reservoir thickness is known to affect the magnitude of corneal edema. 13,20 This approach has been described in detail previously, 14 and an example of this correction procedure is outlined below. A second order polynomial was fitted to each participant's central corneal edema data as a function of fluid reservoir thickness measured under open-eye conditions as described by Fisher et al 13 These individual polynomial equations were then used to estimate the magnitude of corneal edema because of a difference in fluid reservoir thickness, rather than the variable of interest (lens thickness) and the measured corneal edema was then corrected to account for this (Table 1).…”