Effects of scleral-lens oxygen transmissibility on corneal thickness: A pilot study

Abstract

To investigate the effect of various oxygen transmissibilities (Dk/t) of scleral lenses and corneal thickness recovery time from overnight eye closure with patching on corneal edema during 5 h lens wear. Methods: Scleral lenses (hofocon A, 15.6 mm diameter) were worn bilaterally with three different Dks (100, 140, and 160 Barrer). Central and peripheral corneal thickness (CCT and PCT) were measured using optical coherence tomography. Four subjects were randomly selected for one additional visit and asked to patch one eye before night sleeping. The patch was not removed until lens insertion to avoid corneal deswelling. Then CCT of both eyes was measured. Results: Ten neophytes with healthy eyes participated in the study. Mean [95% CI] Dk/t of the study lenses was 32.0 [29.2, 34.7] hBarrer/cm. Mean [95% CI] CCT immediately upon lens insertion and after 5 h of lens wear were 532.4 [520.3, 544.5] μm and 538.7 [526.5, 551.0] μm, respectively. Mean [95% CI] percentage change (%Δ) in CCT was 1.2% [0.9%, 1.5%], 1.2% [0.9%, 1.4%], and 0.8% [0.6%, 1.1%] for CCT, nasal PCT, and temporal PCT, respectively. There was an inverse relationship between temporal Dk/t and %ΔPCT (p < 0.05) while Dk/t was not found significantly associated with either CCT or nasal PCT. The patched eyes maintained a relatively stable CCT and showed progressive deswelling, starting and ending with 2.8% and 0.6%, respectively. In contrast, the unpatched eyes swelled, starting with nearly 0% and ending with 0.7% with a maximum swelling of 1.8%. Conclusion:There was limited amount of corneal edema induced by short-term scleral lens wear with lens Dk/t ranging from 21 to 47 hBarrer/cm and lenses with lower lens Dk/t did not induce significantly higher corneal swelling. Scleral lens insertion soon after overnight eye closure with patching did not introduce additional swelling for young and healthy eyes.

Limbal Metabolic Support Reduces Peripheral Corneal Edema with Contact-Lens Wear

“…Additionally, under extreme hypoxic conditions, swelling is very sensitive to small changes in oxygen tension. 11 Thus, our proposed 2D metabolic model agrees well with clinical central-corneal-edema measurements, 1 , 9 , 11 , 41 and with the swelling-profile data of Wang et al 26 using consistent parameters.…”

“…That is, the maximum in swelling is shallow. Previous clinical 1 , 32 , 41 , 47 and mathematical-modeling efforts 9 , 11 of central corneal edema, therefore, provide satisfactory gauges of maximum edema during contact-lens wear for open eye. However, as the effect of oxygen tension on edema is significantly greater during extreme hypoxic states (e.g., closed-eye with lens oxygen Dk/L <20 hBarrer/cm for SL and <15 hBarrer/cm for SCL wear), 1 , 11 a small difference in lens oxygen Dk/L from the center to mid-periphery may result in a large difference in edema between those regions if the cornea is undergoing significant hypoxia.…”

“…The metabolic model compares well to measured central corneal edema in percentage swelling versus oxygen Dk/L curves for SCLs 1,9 and for SLs. 11,41 Available periphery or mid-periphery swelling curves are sparse. Instrument imprecision results in less reliable measurement of edema at the periphery than at the center because of the limitations of eye fixation and determination of a repeatable noncentral location before and after lens wear.…”

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

“…1 provides accurate swelling predictions for ESCL wear. With ESL wear, the PoLTF thickness is smaller at the periphery than at the center and provides a PoLTF thickness profile representative of commercially available SLs [21,34].…”

“…Moreover, chronic corneal hypoxia induced by 20 years of continuous PMMA contact-lens wear leads to endothelial polymegathism and potentially results in a decline of the cornea's ability to deswell [19]. These clinical risks motivated the development of oxygen-permeable lens materials such as silicone hydrogels and acrylates to minimize corneal hypoxia during contact-lens wear [20][21][22][23][24][25].…”