THE SHAPE OF THE CORNEAL APICAL ZONE AFTER EXCIMER PHOTOREFRACTIVE KERATECTOMY

Applying an experimental photo-keratoscope, which assesses the shape o f cornea within the pupillary region, to a group of subjects who have undergone excimer laser photorefractive keratectomy over a central 4 m m chord diameter of the cornea, we report the shape of the typical cor nea within the ablated zone conforms to a steepening ellipse (average shape factor, 1.25). A statistically significant difference in the mea n shape factor (asphericity) between the photoablated and the normal c ornea (average shape factor 0.89) was not confirmed. However, there is more variability in the shape factors found in the photorefractive ke ratectomy group compared with normals, within the same distance from t he corneal apex. Using the criterion of overlap within two standard de viations, averaging the vertical horizontal meridians, 75% of photoref ractive keratectomy eyes fall within the shape factor limits of the no rmal eye group. In all cases the post-ablated corneal surface was foun d to be regular in terms of surface quality alone. The excimer photore fractive keratectomy technique is therefore a clinically acceptable me thod of refractive surgery.