Hydration effects on corneal topography
P. J. Ousley and M. A. Terry
Lions Eyebank of Oregon Corneal Research Laboratory, Legacy Good Samaritan Hospital and Medical Center, Portland, USA.
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.
