Flap protection during laser-assisted in situ keratomileusis improves refractive outcomes in high myopic astigmatism

Abstract

Purpose: Subtle irregularities in the corneal flap may affect laser-assisted in situ keratomileusis (LASIK) outcomes. The aim of this study was to evaluate flap protection during ablation in myopic astigmatic patients. Methods: Medical files and corneal topographies of consecutive patients with myopic astigmatism (>2.5 D) that underwent LASIK were retrospectively reviewed. The visual and refractive outcomes with and without flap protection during the procedure were compared. We calculated and compared safety index, efficacy index, index of success (Alpins vector analysis) and ratio between nasal and temporal ablation. Results: We included 57 subjects that fulfilled inclusion criteria. Patients in the flap guarding group were similar to patients in the no-guarding group, in terms of pre-operative parameters and similar treatment zones were used in both groups. Post-operatively, the flap guarding group had a better efficacy index (1.08 ± 0.17 vs. 0.96 ± 0.24, P = 0.04) and index of success (0.16 ± 0.07 vs. 0.23 ± 0.17, P = 0.04). The proportion of subjects with more than double nasal over-ablation ratio (>200%) was significantly lower in the guarding group compared to the no-guarding group (04.2% [1/23] vs. 32.3% [11/34], P = 0.02). No significant differences were found between groups in terms of post-operative safety index, uncorrected visual acuity, best-corrected visual acuity, sphere, cylinder and keratometry. Conclusion: Guarding the flap during high myopic astigmatic LASIK was associated with better visual and refractive outcomes.