Analysis of the factors affecting decentration in photorefractive keratectomy and laser in situ keratomileusis for myopia

To evaluate the relationship between ablation zone decentration measured by corneal topography and various factors such as sex, age, order of operation, preoperative sedative prescription, ablation diameter and depth, type of procedure (photorefractive keratectomy = PRK, laser in situ keratomileusis = LASIK), and the use of a passive eye tracker, we examined the data of 80 eyes in 50 patients. The patients received PRK (43 eyes in 30 patients) or LASIK (37 eyes in 20 patients), and were followed for 3 months postoperatively. Statistical analysis of the data was performed using t-test, ANOVA and multiple regression analysis. The overall average ablation decentration from the pupil center was 0.43+/-0.27 mm, 0.35+/- 0.22 mm in PRK and 0.47+/-0.30 mm in LASIK. Overall 91.3% of patients were decentered less than 0.75 mm and 95.0% were decentered less than 1.00 mm, while 93.9% of patients were decentered less than 0.75 mm in PRK and 88.7% were decentered less than 0.75 mm in LASIK. The most meridional displacement was toward the superonasal quadrant; 46% in PRK and 51% in LASIK. There was less decentration in males, in the 2(nd)-operated eye, in older age, PRK, in larger ablation diameter, and in shallower ablation depth, but these differences were not statistically significant.