A New Slant on Toric Intraocular Lens Power Calculation

PURPOSE: The AcrySof Toric intraocular lens (IOL) (Alcon Laboratories, Inc., Fort Worth, TX) is designed to correct corneal astigmatism ranging from 0.67 to 4.11 diopters (D). The authors reviewed the clinical outcomes of this IOL and investigated possible improvements of the online calculator provided by the manufacturer. METHODS: Review of published studies. RESULTS: The AcrySof Toric IOL can provide good results, although a mean overcorrection or undercorrection relative to the intended correction has been found by some authors. Stability over time has been reported to be excellent. Rotation occurs mainly in the first postoperative month and is greater in eyes with a longer axial length due to the larger capsule size. The online calculator of this IOL may be improved by considering the posterior corneal astigmatism and better calculating the conversion of the IOL cylinder from the IOL plane to the corneal plane, which may be inaccurate for two reasons. First, given the variable distance between the IOL and the cornea in short and long eyes, the fixed ratio (1.46) provided by the manufacturer cannot be used to calculate this conversion. Second, the online calculator does not take into account the effect of varying IOL sphere power. CONCLUSION: The AcrySof Toric IOL is a reliable choice to correct corneal astigmatism at the time of cataract surgery. Results will be improved once the online calculator by the manufacturer considers the posterior corneal astigmatism and the variable ratio between the toricity at the IOL and corneal plane.