To evaluate the relative partial pressure in oxygen (pO2
) at the corneal surface under Boston XO2 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 pO2
. Corneal pO2
s were measured with an oxygen electrode after 5 minutes of (1) corneal exposure to calibrating gases with various pO2
or of (2) SL wear. Decays in pO2
were modeled to an exponential. Linear regression between exponent k of these decays and calibrating gas pO2
s allowed for the calculation of corneal pO2
under SL. Differences between pO2
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 pO2
of 8.52 ± 0.51 and 6.37 ± 0.28% for SL200 and SL400. These values were close to measured pO2
: 9.07 ± 0.86 and 6.19 ± 0.87% (mean ± SEM) (P
< .05) for SL200 and SL400, respectively. Both pO2
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.