ABSTRACT
BACKGROUND: Femtosecond laser-assisted LASIK (FS-LASIK) can make ultra-thin corneal flap accurately. MEL 90 excimer laser provides Triple-A ablation mode, which significantly reduces the amount of corneal tissue cutting. This study aimed to investigate the visual and refractive outcomes in patients with high myopia after thin-flap FS-LASIK using the 500 Hz pulse rate of the Triple-A profile. METHODS: This prospective study included 90 eyes from 90 patients received thin-flap FS-LASIK using the 500 Hz pulse rate of the Triple-A profile. According to the pre-operative spherical equivalence (SE), the treated eyes were divided into two groups: the first group (ranged from - 9.0D to - 6.0D) and the second group (ranged from - 11.15D to - 9.0 D). The parameters evaluated pre-operatively and 6 month post-operatively included uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), SE, efficacy and safety index, posterior central elevation, and corneal higher-order aberrations (HOAs). RESULTS: The efficacy indexes were 1.149 ± 0.150 for the first group and 1.173 ± 0.136 for the second group (P > 0.05), whereas safety indexes were 1.135 ± 0.154 and 1.158 ± 0.137 (P > 0.05) respectively. Moreover, 93.8 and 90.6% of patients had an UDVA of 20/20, 51.2 and 49.8% had a UDVA of 20/16 for the first and second groups, respectively; yet, there were no significant differences between both groups at the 20/20 and the 20/16 levels (P > 0.05). 84 and 100% of the firse group patients had a SE within ±0.5 D and ± 1.0 D, and 82 and 100% of the second group patients. There was no significant myopia regression in both groups after 6 months follow-up. At 1, 3 and 6-month after surgery, there were no significant differences in the posterior central elevation between the two groups (P > 0.05). The induction of total HOAs, spherical aberration, and horizontal coma in the first group were significantly less than that in the second group at the 6- month follow-up (P < 0.05), while the differences of the RMS value of vertical coma between both groups were not significant (P > 0.05). The ablation was significantly associated with the post-operative increase in total HOAs, spherical aberration and horizontal coma (P < 0.05),but not with vertical coma (P > 0.05). CONCLUSION: Our results indicate that using the Triple-A ablation profile of the MEL 90 excimer laser associated with thin-flap is a safe, efficient, and predictable method to correct SE up to - 11.15D. However, for patients with high myopia, under the premise of ensuring a certain optical zone diameter, the ablation depth should be minimized to reduce the increase of the post-operative HOAs so as to improve the visual quality.
