Central and peripheral corneal swelling accompanying soft lens extended wear.

Central and peripheral corneal thickness changes were measured after 3 hr of eye closure with and without contact lens wear. Spun cast and lathe cut hydrogel extended wear lenses of -1.25, -6.00, and -9.00 D were used. Each of these conditions produced 25 to 50% less swelling in the peripheral than in the central cornea. Central swelling was greater with higher minus spun cast lenses, but not related to the power of the lathe cut lenses. Higher minus lens powers of both lens types produced greater peripheral swelling. Differences between central and peripheral swelling were smaller with the higher minus lenses, indicating little, if any, averaging of tear oxygen tension under the lens when the eyes are closed. The mechanism resulting in less peripheral corneal swelling is likely to be caused by an anatomical "clamping" at the corneal limbus.