Effect of treatment zone diameter on the clinical results of femtosecond laser-assisted in situ keratomileusis and trans-photorefractive keratectomy for the correction of myopia

Aim: The aim of this study is to examine and compare the effect of treatment zone diameter on the results of femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and transphotorefractive keratectomy (PRK) procedures performed for the treatment of myopia. Materials and Methods: This was a retrospective cohort study. The study reviewed medical files of patients who underwent trans-PRK (2630 eyes) and FS-LASIK (879 eyes) in which different treatment area diameters were used. For each type of surgery, the eyes were divided into three groups, based on the treatment zone diameter (6 mm, 6.5 mm. and 7 mm). Results: In the FS-LASIK group, there was no difference in both the safety and efficacy indices or in the distance from the intended result between the groups (P = 0.79, P = 0.57, and P = 0.09, respectively). In myopic trans-PRK, a treatment area of 7 mm was associated with worse outcomes in terms of safety (P = 0.01) and efficacy (P < 0.01) in comparison with the other groups. In addition, a treatment zone of 7 mm was associated with a significantly larger distance from the refractive target (P < 0.001). There were no significant differences between the 6 mm and 6.5 mm groups in any outcome measure. These results recurred in a multivariate analysis, after correcting them for age, gender, pre-operative refractive error, and pachymetry. Conclusions: Different treatment zone sizes gave similar results in FS-LASIK, while in trans-PRK, a 7 mm zone was associated with inferior outcomes in comparison to smaller treatment zones. Hence, in trans-PRK, we recommend choosing a treatment zone smaller than 7 mm while taking pupillometry into account and opting FS-LASIK whenever a very large treatment zone is required.