Correction of astigmatism with small-incision lenticule extraction: Impact of against-the-rule and with-the-rule astigmatism

Abstract

To determine the influence of against-the-rule (ATR) and with-the-rule (WTR) astigmatism on the outcomes of small-incision lenticule extraction for myopic astigmatism. University eye clinic, Aarhus, Denmark. Retrospective case series. One eye of each patient had small-incision lenticule extraction for astigmatism of 1.00 diopter (D) or more. Surgery was performed with a Visumax femtosecond laser. Subjective refraction and Scheimpflug tomography (Pentacam HR) were performed preoperatively and 3months postoperatively. Cylinder data were evaluated by vector analysis and correlation analyses. Multiple linear regression was used to predict magnitude of error from age, sex, left or right eye, target-induced astigmatism (TIA), subjective ATR/WTR astigmatism, cap diameter, cap thickness, incision width, and back-surface astigmatism. The study enrolled 829 patients (505 women; median age 37years). The mean preoperative subjective cylinder was 1.76 D ± 0.86 (SD). Overall, 66% and 95% of patients achieved a refractive cylinder within ±0.50 D or ±1.00 D, respectively. Astigmatism was WTR in 73% of eyes and ATR astigmatism in 16% of eyes. The linear regression model significantly predicted the magnitude of error (R2=0.23, P<.001), with TIA contributing -0.15 D per attempted diopter and subjective ATR astigmatism contributing a constant 0.32 D (both P<.001). No other parameters had a significant impact on the outcome. Almost 25% of the variation after small-incision lenticule extraction for myopic astigmatism might be explained by the size of the attempted cylinder correction and ATR/WTR astigmatism. Incorporating these parameters in preoperative planning might produce more consistent results in high cylinder corrections.