Effect of Excimer Laser Photorefractive Keratectomy on the Induction of Astigmatism in Rabbits

ABSTRACT

Twenty eight rabbit eyes which underwent astigmatic photorefractive keratectomy with excimer laser were analyzed to evaluate the effect of excimer laser photorefractive keratectomy on high astigmatic refractive error. Non-astigmatic eyes were divided into 4 groups according to their operative technique for inducing astigmatism(Group I 50micrometer ablation with no astigmatism, Group II 3.00 diopter with the rule astigmatism, Group III 6.00 diopter with the rule astigmatism, Group IV 9.00 diopter with the rule astigmatism). During the follow-up period, changes of astigmatism were examed with corneal topography, The results were as follows; 1. Two months after surgery, the mean achieved astigmatisms were 0.23(Group I), 1.78(Group II), 2.63(Group III) 2.65 diopters(Group IV), respectively. 2. Mean astigmatic induction rates of the group II,III and IV were 59.4%, 48.3% and 29.48%, respectively, Astigmatic induction rate of group II, in which the attempted astigmatism was -3.00 diopters, was highest(P<0.05) 3. Highly achieved astigmatism at postoperative 7 days regressed in all groups except group I(P<0.05). The regression was most significantly progressed in group IV, but the regression pattern did not reveal any statistically significant difference between the groups(P<0.05) 4. In SEM study, the rabbit cornea samples showed the different irregularities. Deeper ablation group tissues exhibited a much rougher surface appearance than shallow ablation group tissues. In this study, it was concluded that the achieved astigmatism and induction rate of astigmatism were statistically significant correlation(P<0.05), but the induction rate was smaller compared to the attempted astigmatism, and increased tendency for regression.