The effect oflens sphere and cylinder power on residual astigmatism and its resolution after toric intraocular lens implantation

PURPOSE: To analyze correlations between residual refractive cylinder (and its correction through lens reorientation) with the sphere and cylinder power of the toric intraocular lens (IOL) implanted. METHODS: An online toric back-calculator (www. astigmatismfix.com) allows users to input toric IOL planning data, along with postoperative IOL orientation and refractive results; these data are used to determine the optimal orientation of the IOL to reduce refractive astigmatism. This was a retrospective data analysis; aggregate historical data were extracted from this calculator to investigate the relationship between residual refractive astigmatism and IOL cylinder and sphere power. RESULTS: A total of12,812 records, 4,619 ofwhich included IOL sphere power, were available for analysis. There was no significant effect ofsphere power on residual refractive astigmatism (P =.25), but lower IOL cylinder powers were associated with significantly lower residual refractive astigmatism (P <.05). The difference between the intended and ideal orientation was higher in the lower IOL cylinder power groups (P <.01). Overcorrection ofastigmatism was significantly more likely with higher IOL cylinder power (P <.01), but not with sphere power (P =.33). Reorientation to correct residual refractive cylinder to less than 0.50 diopters (D) was more successful with IOL cylinder powers of 1.50 D or less (P <.01); IOL sphere power had no apparent effect. CONCLUSIONS: There were significant effects of IOL cylinder power on residual refractive astigmatism, the difference between intended and ideal orientation, the likelihood ofovercorrection, and the likelihood ofastigmatism reduction with lens reorientation. IOL sphere power appeared to have no such effects.