[Undersurface ablation of the corneal flap for LASIK enhancement].

OBJECTIVE To study the efficacy and safety of retreatment in LASIK surgery, comparing under surface ablation of the corneal flap and stromal bed ablation techniques. METHODS The patients studied were those who had LASIK enhancement because of a residual negative refractive error, and were divided in two groups: a Control group of 14 eyes that had ablation of the residual stromal bed and a Study group of 14 eyes that had ablation of the undersurface of the flap. In the Study group we included patients in whom we calculated that the post-enhancement treatment of the residual stromal bed would be less than 300 microns. We compared the refraction, visual acuity and cornea pre and post-retreatment, three months later. RESULTS Prior to retreatment, both groups were similar and no statistically significant differences were found in age, sex, pachymetry, corneal curvature or residual refraction. Ablation was 21.5 (SD 11) microns in study group and 22.6 (SD 7) microns in control group (p=0.796). Post-retreatment refraction was statistically lower in both groups than before the procedure (p<0.01), however there were no differences between the control and study groups. Visual acuity improved after retreatment in both groups (p<0.01) but no statistically significant differences were found between control and study groups. No patient lost two lines of visual acuity. We observed slight alterations in the corneal flap in both groups. CONCLUSIONS In our study, the undersurface retreatment technique produced similar results to those achieved using conventional stromal bed techniques with both being effective and safe in patients with a small residual negative refractive error.