Abstract
Purpose: :
Since thinner corneas should have higher stromal Dk/t values (due to the smaller t-factor), do keratoconic corneas, which are relatively thinner than their normal counter-parts, exhibit less hypoxic stress immediately following a period of anterior surface blockage from the atmosphere?
Methods: :
Using a polarographic electrode with standard reservoir, oxygen uptake rates were measured under normal (155 mm Hg) and hypoxic (0 mm Hg) oxygen partial pressure conditions (induced by 300 sec of static PMMA contact lens wear) were made on 12 corneas (six normal, and six with at least one physical indication of moderate keratoconus in addition to keratometric values in the 45 to 52 D range). Only one cornea of each subject was used, it being measured at the center, and at superior, inferior, nasal and temporal locations 3mm from the center. All hypoxic recovery rates were ratioed to the normal uptake rate for each site. ANOVA and post hoc testing was used for discerning statistical differences among and between mean recovery oxygen uptake rates.
Results: :
From the mean uptake rates at each location, direct site-to-site post-hypoxic recovery rates and corneal thickness comparisons were made. All keratoconic sites were found to be thinner and to have lower hypoxic recover rates than their normal corneal counterparts, but none were found to be significantly different at the p=0.05 level.
Conclusions: :
On a site-to-site comparison basis, thinner keratoconic corneas did manifest lower post-hypoxic stress following a period of anterior surface blockage from the atmosphere. This appears due to the relative thinness of the keratoconic stroma, i.e., resulting from the reduced resistance of a lower Dk/t pathway from the aqueous oxygen source.
Keywords: cornea: basic science • keratoconus • oxygen