Toric intraocular lens outcome using the manufacturer's prediction of corneal plane equivalent intraocular lens cylinder power

Abstract

Objectives: To describe the refractive outcome of toric intraocular lens (IOL) implantation by comparing the postoperative refractive astigmatism with the preoperative keratometric astigmatism target. Method: In a university department of a publicly funded hospital, 38 eyes of 29 patients underwent routine cataract surgery with insertion of a toric implant (SN60TT AcrySof Toric). Surgically induced astigmatism was derived using vector analysis of refractive outcome vs predicted postoperative keratometric astigmatism and compared with the targeted induced astigmatism. Results: Postoperative remaining refractive astigmatism of 0.97 diopters (D) was achieved vs a target of 0.61 D. A mean (SD) surgically induced astigmatism value of 1.78 (0.89) D was derived compared with a mean (SD) targeted induced astigmatism value of 1.58 (0.47) D (calculated by the manufacturer's online calculator, which predicts IOL corneal plane equivalent cylinder power and postoperative keratometric cylinder). Conclusions: Toric IOLs are a safe, predictable method of astigmatic correction. However, some remaining astigmatism is commonly present owing to the necessary nonzero astigmatic targets imposed by the steps between IOL cylinder powers, variability of axis, and power effects of surgical incisions as well as by underestimation of the corneal plane cylinder power of the IOLs by the manufacturer.