Swelling and deswelling of rabbit corneas in response to rigid gas permeable, hydrogel and elastomer contact lens wear

We determined diurnal variation in corneal thickness in rabbits prior to and following overnight wear of: (i) selected rigid contact lenses with different Dk values; (ii) hydrogel lenses of low and high water content; and (iii) elastomer lenses. The degree of contact lens-induced corneal swelling observed during 24 hours of lens wear, and the rates of deswelling in the subsequent 24 hours, correlated well with the different oxygen transmissibilities of the individual RGP contact lenses. The greatest swelling (21.6 ± 5.4%) followed the wear of PMMA lenses. The least swelling, 2.9 ± 4.0%, followed the wear of rigid gas permeable (RGP) Menicon SF-P (melafocon A) lenses, a value nearly indentical to the swelling observed in the morning following sleep without lenses, (0.0 ± 3.1%). By contrast, low-water content hydrogel soft contact lens use was associated with drastic corneal deswelling rates (-15.1 ± 4.5%) during the hours after lens wear. The difference between these and control corneas was significant by paired t-test (P<0.01). Eyes wearing high water content lenses had less deswelling than eyes with their low-water counterparts. Corneal swelling produced by elastomer lenses was similar to that seen with RGP lenses.