Influence of Preoperative Astigmatism Type and Magnitude on the Effectiveness of SMILE Correction.

PURPOSE: To assess the effectiveness of small incision lenticule extraction (SMILE) as a function of the astigmatism level and type.

METHODS: A total of 102 right eyes were included in this study. Refractive astigmatism and corneal astigmatism measured with Scheimpflug technology were retrieved from the preoperative visit and the 3-month follow-up visit. Patients were split into three groups according to the preoperative refractive astigmatism (0.50, 0.75 to 1.25, and 1.50 diopters [D] or greater) and the effectiveness among each group was evaluated according to the with-the-rule (WTR), against-the-rule (ATR), and oblique classifications. The standard Alpins method was used for the analysis.

RESULTS: Resultant astigmatism was not associated with its preoperative classification when the total sample was considered, but a significant association emerged between the presence of resultant astigmatism and its preoperative classification in the 1.50 D or greater group. The magnitude of error was significantly lower in the WTR (median: -0.30 D) than in the oblique and ATR astigmatism groups, resulting in a coefficient of adjustment of 1.13 for WTR astigmatism of 1.50 D or greater but not for the other types.

CONCLUSIONS: Astigmatism correction with SMILE is predictable for astigmatism lower than 1.50 D without the need to apply a correction. However, higher undercorrection is present in WTR astigmatism of 1.50 D or greater. [J Refract Surg. 2019;35(1):40-47.].