Diurnal changes in corneal topography have been documented to be greater in eyes following radial keratotomy that in normal eyes. To determine whether substantial changes of this nature result from corneal incisions in general or are a specific complication of radial keratotomy, we examined 12 corneas (10 patients) after penetrating keratoplasty for diurnal changes, using a computerized corneal topographic analysis system. Diurnal changes in keratometry readings, central corneal thickness, intraocular pressure, and refraction also were analyzed. From morning to evening, central corneal curvature flattened by an average of 0.74 ± 0.18 diopters in eight eyes (67%), and steepened by an average of 2.00 ± 0.53 D in four eyes (33%). Diurnal changes in central corneal thickness were correlated with diurnal changes in central corneal curvature (r = 0.63.P < .05). These data suggest that changes in corneal thickness over the course of the day may partially account for the changes in corneal curvature demonstrated to occur following penetrating keratoplasty.
To examine the effects of surface dehydration on corneal surface morphology before and after photorefractive keratectomy, corneas of fresh porcine eyes were deeprthelialized and then immediately fixed or treated according to one of six protocols (four eyes per protocol): dehydrated under the illumination of an operating microscope; dehydrated and then rehydrated with topically applied balanced salt solution; photorefractive keratectomy; photorefractive keratectomy followed by surface dehydration; or photorefractive keratectomy followed by dehydration and subsequent rehydration.
Surface smoothness (S) was measured with an image analysis system. The surfaces of the unablated corneas were smooth (S = 0.992 ± 0.002), and dehydration did not significantly (P = .7) influence the morphology. After ablation, dehydration resulted in apparent fragmentation of the superficial lamellae, with consequent roughening of the surface (P = .0001). Rehydration was only partially successful in reducing surface irregularity. We conclude that corneal dehydration during and following photorefractive keratectomy roughens the corneal surface and should be carefully avoided.
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