This study evaluated the outcomes of small-incision lenticule extraction (SMILE) surgery in astigmatic eyes, with or without correction for cyclotorsion.
Study design
The authors studied 84 eyes of 84 consecutive patients who had preoperative myopic astigmatism of −0.75 D or more and underwent SMILE surgery over a 2-month period. Investigators randomly assigned 30 eyes to undergo standard SMILE surgery (S group) and 54 eyes to undergo cyclotorsion-compensated SMILE surgery (CC group). The study assessed visual acuity and refractive outcomes, with attention to vector analysis of astigmatism before surgery and at 6 months after surgery.
Outcomes
Cyclotorsion ranged from 0 to 10 degrees, with average position-related cyclotorsion of 1.7 and 2.19 degrees in the S and CC groups, respectively (P=0.26). Six months after surgery, the groups showed a significant difference in uncorrected and corrected distance visual acuity. The S and CC groups had UDVA values of 0.02 and −0.04 logMAR, respectively (P=0.04); and CDVA values of 0.016 versus -0.07, respectively (P=0.01).
Six months after treatment, surgical outcomes in the CC group were significantly better than those of the S group. In the CC group, the UDVA was 20/16 or better in 45 eyes (83%) and 20/20 or better in 52 eyes (96%). By contrast, in the S group, the UDVA was 20/16 or better in 10 eyes (33%) and 20/20 or better in 24 eyes (80%).
The mean cylinder values before surgery were −1.67 D and −1.72 D in the S and CC groups, respectively. Vector analysis of astigmatism yielded better outcomes in the CC group, where only 3 of 54 eyes (5.6%) had low degree astigmatism. By contrast, 5 of 30 eyes (16.7%) in the S group had uncorrected cylinder. Better astigmatism correction outcomes were achieved in the CC group (1.68 D), compared with the S group (1.3 D, P=0.04). Additionally, the angle of error was within −5 to 5 degrees in 92.5% eyes in the CC group and 66.7% eyes in the S group (angle of error, S group: 6.7 versus C group: 3.2 ; P=0.02).
In the CC group, 31 of 54 eyes (57.4%) showed no change, 18 eyes (33.3%) gained 1 or more lines, and no eyes lost 2 lines of CDVA. Meanwhile, in the S group, 15 of 30 eyes (50%) showed no change, 5 eyes (16.7%) gained 1 or more lines and 2 eyes (6.6%) lost 2 lines of CDVA.
Limitations
Cyclotorsion correction was performed manually with ink marks because there is no automatic iris registration or tracking currently available with the VisuMax femtosecond laser system. The study included patients of all levels of astigmatism greater than or equal to -0.75 D; there was no further subgroup analysis comparing outcomes of patients with low versus high levels of astigmatism.
Clinical significance
Studies have shown that when eye cyclotorsion is greater than 2 degrees and not compensated, cylinder correction might be adversely influenced and significant aberrations can be induced during laser treatment. This is especially true in patients with high astigmatism. SMILE surgery combined with cyclotorsion error compensation yielded a significant improvement in surgical outcomes regarding visual acuity, refractive cylinder and safety profile.