Central and peripheral oxygen transmissibility thresholds to avoid corneal swelling during open eye soft contact lens wear

Abstract

This study was designed to derive central and peripheral oxygen transmissibility (Dk/t) thresholds for soft contact lenses to avoid hypoxia-induced corneal swelling (increased corneal thickness) during open eye wear. Central and peripheral corneal thicknesses were measured in a masked and randomized fashion for the left eye of each of seven subjects before and after 3 h of afternoon wear of five conventional hydrogel and silicone hydrogel contact lens types offering a range of Dk/t from 2.4 units to 115.3 units. Curve fitting for plots of change in corneal thickness versus central and peripheral Dk/t found threshold values of 19.8 and 32.6 units to avoid corneal swelling during open eye contact lens wear for a typical wearer. Although some conventional hydrogel soft lenses are able to achieve this criterion for either central or peripheral lens areas (depending on lens power), in general, no conventional hydrogel soft lenses meet both the central and peripheral thresholds. Silicone hydrogel contact lenses typically meet both the central and peripheral thresholds and use of these lenses therefore avoids swelling in all regions of the cornea.

The significance of oxygen during contact lens wear

“…It is clear from this summary that the potential barrier to atmospheric oxygen created by a contact lens will be a critical factor in altering the aerobic/anaerobic metabolic fraction and thus in precipitating corneal swelling. Data from computer models [56] and clinical studies [57,58] are in agreement that the amount of induced swelling increases sharply as lens transmissibility decreases.…”

“…In the open eye there is good agreement between the conducted studies which report lens transmissibilities in the range 20-24 barrers/cm as sufficient to prevent central swelling [58,156,157]. Closed eye studies also agree reasonably well, suggesting that transmissibility values in the range 75-87 barrers/cm [57,158,159] limit central swelling to about 4%, which is approximately that experienced during sleep without lenses.…”

“…The observation that lenses with peripheral transmissibility of around 36 barrers/cm did not cause excessive redness during daily wear clinical studies [85] has been construed as indicating that the true limbal redness limit is nearer to this lower value [58]. However, since there are problems with this interpretation due to the potentially inaccurate procedure used to determine the peripheral transmissibility of the lenses in the original work, scope remains for further work in this area.…”

“…However, only one group have looked directly at the relationship between peripheral swelling and transmissibility and then only in the open eye, where 33 barrers/cm was found to be the acceptable level [58]. The fact that closed eye peripheral swelling was still evident during wear of lotrafilcon A lenses suggests that the transmissibility of even these lenses (typically about 100 barrers/cm, but not stated in this particular study) was below that ideally necessary [161].…”

The Prevalence and Impact of High Myopia

“…[90][91][92] Corneal swelling is also related to hypoxia and is primarily impacted by lens power 93 and lens material. 94 Although corneal swelling is greatly reduced with silicone hydrogel lenses, overnight wear of 210.00-D lenses still causes more swelling in the corneal periphery compared with overnight wear of a 23.00-D lens. 95 Visual Acuity, Contrast Sensitivity, and Overall Image Quality Contrast sensitivity functions have been determined for emmetropes and participants with different levels of myopia corrected with spectacles or contact lenses.…”