Outcome of toric intraocular lens implantation after adjusting for anterior chamber depth and intraocular lens sphere equivalent power effects

Objective: To describe the refractive outcome of toric intraocular lens (IOL) implantation by taking into account the effect on astigmatic outcome of the anterior chamber depth and the sphere power of the IOL, and to examine whether the predictability of the toric effect can be improved. Method: In a university department in a publicly funded hospital, 38 eyes of 29 patients underwent routine cataract surgery with insertion of a toric implant (SN60TT AcrySof Toric). The corneal plane effective cylinder power of the IOL was calculated, including the effect on this value of the anterior chamber depth and pachymetry and of the sphere power of the IOL. Results: The mean (SD) corneal plane equivalent cylinder power of the IOL predicted preoperatively by the manufacturer as 1.58 (0.47) diopters (D) vs 2.02 (0.64) D by us (calculated using predicted postoperative anterior chamber depth and IOL sphere values). The mean (SD) measured postoperative value was 1.78 (0.89) D, which was better predicted by us. Conclusions: The manufacturer currently appears to underestimate the corneal plane effective cylinder power of its toric IOLs. Improved outcome could be achieved by estimating the effective corneal plane cylinder power of the IOL, as altered by the anterior chamber depth and pachymetry and by the IOL sphere power, but this is currently not addressed by the manufacturer.