Comparison of Astigmatic Correction With and Without Cross-axis Alignment During Small Incision Lenticule Extraction

Abstract

PURPOSE: To compare clinical outcomes after astigmatism correction via small incision lenticule extraction (SMILE) with and without cross-axis alignment. METHODS: This prospective study included patients who underwent SMILE with astigmatism of greater than 0.75 diopters (D). In the alignment group, head position was readjusted by cross-axis alignment before the standard SMILE procedure. First, the cross-axis was aligned to corresponding green lines on the headrest. Then, the patient's head was adjusted to align the horizontal line to the outer canthus of both eyes and align the vertical line connecting the midpoints of the eyebrows and the bridge of the nose. Changes in ocular parameters were assessed, and vector analysis was performed 6 months postoperatively. RESULTS: The alignment and control groups included 61 and 54 eyes, respectively. Postoperatively, the safety and efficacy indices were comparable between the two groups. Notably, refractive cylinder differed significantly in the alignment group (−0.23 ± 0.26 D) compared to the control group (−0.36 ± 0.26 D) ( P = .007). Forty-eight (78.7%) and 32 (59.3%) eyes in the alignment and control groups ( P = .03) achieved an angle of error within ±5°, respectively. Vector analysis showed a significantly lower difference vector and a significantly better index of success in the alignment group than that in the control group (0.24 ± 0.25 vs 0.35 ± 0.24, P = .003 and 0.20 ± 0.22 vs 0.29 ± 0.22, P = .02, respectively). Moreover, the change in corneal trefoil differed significantly between the groups ( P < .001). CONCLUSIONS: Cross-axis alignment for head positioning in SMILE significantly minimizes axis misalignment and reduces undercorrection astigmatism in myopic astigmatism correction. This technique is a non-invasive and effective method, especially for beginners. [ J Refract Surg . 2022;38(10):624–631.]