Toric Calculations

Abstract

AbstractOlder toric calculators were limited by the use of the keratometric astigmatism (with no information about posterior corneal curvature) and the adoption of a fixed ratio between the cylinder at the IOL plane and the cylinder at the corneal plane. A discussion about these issues that have been solved by newer calculators is provided along with a brief introduction to the influence of IOL tilt on the refractive outcomes of toric IOLs. The Abulafia-Koch, Barrett, Barrett True-K, EVO, Goggin, Holladay, Johnson & Johnson, Kane, Næser-Savini, Rayner, and Zeiss toric calculators are described. According to the published studies, the percentage of eyes with an absolute prediction error of the cylinder within 0.50 D ranges between 55 and 79% with calculators estimating Total Corneal Astigmatism (TCA), whereas it is close to 40% with calculators using measured TCA and around 25–30% with calculators using Keratometric Astigmatism (KA).