SL-200

To evaluate the relative partial pressure in oxygen (pO 2 ) at the corneal surface under Boston XO 2 scleral lenses (SL) fitted with targeted clearances of 200 and 400 μm (SL200 and SL400).

During this prospective study, the right eyes of eight normal subjects were fitted with SL200 and SL400. Clearance, validated after 5 minutes of wear with an optical coherence tomograph, was used with lens thicknesses to calculate transmissibility and estimate pO 2 . Corneal pO 2 s were measured with an oxygen electrode after 5 minutes of (1) corneal exposure to calibrating gases with various pO 2 or of (2) SL wear. Decays in pO 2 were modeled to an exponential. Linear regression between exponent k of these decays and calibrating gas pO 2 s allowed for the calculation of corneal pO 2 under SL. Differences between pO 2 s beneath SL200 and SL400 were tested with a mixed ANOVA.

The estimated transmissibility based on thicknesses and clearances (239.7 ± 34.7; 434.5 ± 33.2 μm) predicted a corneal pO 2 of 8.52 ± 0.51 and 6.37 ± 0.28% for SL200 and SL400. These values were close to measured pO 2 : 9.07 ± 0.86 and 6.19 ± 0.87% (mean ± SEM) ( P <. 05) for SL200 and SL400, respectively. Both pO 2 measurements fall short of the theoretical values needed to prevent hypoxia during lens wear (9.9% and above).

As shown in vivo for the first time, an 18‐mm scleral lens fitted with a 400‐μm clearance reduces the oxygen tension available to the cornea by 30% compared to a similar lens fitted with a 200‐μm clearance after 5 minutes of wear.