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Total corneal power more accurately predicts residual astigmatism
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A dual Scheimpflug-Placido tomography method was more accurate than automated keratometry in predicting residual astigmatism after toric IOL implantation, according to a study.
The retrospective cases series included 35 eyes of 35 patients who underwent cataract surgery and implantation of an AcrySof IQ toric IOL (Alcon).
Preoperatively, automated keratometry was performed with the IOLMaster (Carl Zeiss Meditec), and the Galilei system (Ziemer) was used to perform dual rotating Scheimpflug-Placido keratometry.
Prediction error was determined by subtracting preoperative corneal astigmatism from actual corneal astigmatism. Vector analysis was used to calculate actual corneal astigmatism and prediction error.
Mean preoperative corneal astigmatism was 1.61 D with automated keratometry and 1.71 D with total corneal power. Twenty-six eyes (74.3%) had with-the-rule posterior astigmatism.
Mean magnitude of postoperative manifest refractive astigmatism was 0.38.
Eighteen eyes (51%) were corrected, eight eyes (23%) were overcorrected and nine eyes (26%) were undercorrected, according to automated keratometry. Thirteen eyes (37%) were corrected, 12 eyes (34%) were overcorrected and 10 eyes (29%) were undercorrected, according to total corneal power.
Mean magnitude prediction error was similar with automated keratometry and total corneal power.
“However, the automated keratometer method tended to overcorrect [with-the-rule] astigmatism and undercorrect against-the-rule astigmatism. The [total corneal power] technique lacked these biases,” the study authors said.
Disclosure: Hamilton has received honoraria for educational lectures from Ziemer Ophthalmic Systems. The other authors have no relevant financial disclosures.
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