Hydration effects on corneal topography

Objective: To evaluate the effect of corneal thickness changes on the central and paracentral corneal topography in de-epithelialized eye-bank eyes at various stages of hydration. Methods: Corneal topography of 12 eye-bank eyes was measured with a videokeratoscope at the following four stages of hydration: prethinning (mean pachymetry, 0.88 mm), postthinning (0.55 mm), after 15 minutes of rehydration (0.60 mm), and after 30 minutes of rehydration (0.64 mm). Results: Corneal thickness changes were significant between each stage of hydration (P<.05 by repeated-measures analysis of variance). No net astigmatic shifts were observed between any stage of hydration (P=.45). From prethinning to postthinning, dehydration produced average central corneal steepening of 0.44 diopters (P<.001), and average paracentral steepening of 0.89 D (P<.001). Significant changes in corneal power were not measured during normal rehydration until 30 minutes posthydration, when the central cornea had flattened an average of 0.3 D from normal thickness (postthinning) levels (P<.05). Conclusions: Substantive thinning of corneal tissue caused statistically significant but clinically minimal (<1 D) central and paracentral steepening, but smaller corneal hydration changes that can occur during experimental and surgical procedures had little effect on corneal topography.