Osmotically induced central and peripheral corneal swelling in the cat

A number of factors have been suggested to account for the reduced swelling response of the peripheral cornea. The osmotic swelling was determined in 25 adult cats by dripping deionized water onto the cornea for 30 min. The central cornea swelled 62 +/- 19 microns compared to 32 +/- 21 microns for the peripheral cornea. Before treatment, the cat was found to have a very uniform thickness profile, measuring 592 +/- 42 microns centrally, and 585 +/- 46 microns peripherally. The difference in central and peripheral swelling was therefore not due to topographical differences in baseline thickness. Endothelial cell density (ECD) determined with specular microscopy was 2920 cells/mm2 centrally, compared to 3,185 cells/mm2 peripherally. Differences in cell density between the center and periphery are not responsible for the reduced swelling response of the corneal periphery inasmuch as swelling response was not correlated with cell density either in the center of the cornea or in the periphery (r = 0.179 and r = 0.221, respectively). By selecting an animal with a uniform thickness profile and by using an osmotic stimulus, this study has shown that the most likely cause for the reduced swelling response near the limbus is a difference in structural and/or hydration characteristics of the cornea at the limbus.