PHOTOREFRACTIVE KERATECTOMY FOR THE CORRECTION OF MYOPIA AND ASTIGMATISM

Photorefractive keratectomy corrects myopia with or without astigmatis m by decreasing the refractive power of the central cornea. The Collia c matrix formula determines the anterior corneal radius of curvature e xpected to achieve emmetropia. We used the formula as an algorithm for the computer-controlled delivery of the laser beam. The formula was e valuated by using theoretical and clinical cases. We examined the rela tionship between the correction induced by photorefractive keratectomy , the diameter of ablation zone, and the thickness of the ablated corn eal lenticule on the optical axis. Comparison between attempted and ac hieved keratometric readings showed the accuracy of the formula to be in the order of +/- 0.75 diopter.