Influence of Extrinsic and Intrinsic Parameters on Myopic Correction in Small Incision Lenticule Extraction

PURPOSE: To evaluate the influence of different extrinsic and intrinsic parameters on outcomes in eyes with myopia or myopic astigmatism that underwent small incision lenticule extraction. METHODS: This was a multicenter retrospective chart review of three private centers. At last follow-up, 2,564 eyes of 1,524 patients (> 340 patients per center, time span of > 2 years for each center) were analyzed. The effect of different parameters on postoperative spherical equivalent refraction was assessed using univariate linear and multilinear correlations. Seasonal variations in the outcomes were evaluated through a sine fit. The analyses were performed per individual practice and combined. RESULTS: Higher corrections and younger patients showed relative undercorrections (almost 1% per diopter [D] of planned correction or decade of age). Female patients showed relative overcorrections compared to male patients (> 1%). There was a systematic undercorrection (-0.40 D). Other parameters showed statistical significance in one or two practices, but not in all three cohorts. Seasonal variations in postoperative outcomes were found. CONCLUSIONS: Higher corrections, older patients, and gender affected postoperative outcomes in a subtle yet significant manner at all three centers. A system-universal correction, age, and gender-dependent adjustment may help optimize small incision lenticule extraction refractive outcomes. Other parameters and seasonal variations may benefit from an individual center-based adjustment because nomogram adjustment was different for each center. [J Refract Surg. 2019;35(11):712-720.].