To determine a measure of corneal astigma-tism that correlates well with manifest refractive cylinder.
486 right eyes and 485 left eyes were ana-lysed preoperatively on the Zeiss ATLAS™ 9000. Measurements were performed between June 2009 and August 2011. Right eye and left eye data were analysed separately to ensure that observations were independent. Keratometric data were measured with a Topcon(R) OM-4 keratometer.Using all the Placido ring data available from topogra-phy, an astigmatism value was calculated for each ring followed by a summated vector mean on the total rings resulting in a measurement known as corneal topographic astigmatism – CorT. This was then com-pared to the refractive cylinder measured subjectively using the ocular residual astigmatism (ORA). The spread in ORA for the CorT was then compared against other measures of corneal astigmatism: simulated keratometry (SimK), manual keratometry (manK), corneal wavefront (CorW) and paraxial curvature matching (PCM).
CorT (ORA 0.62 +/? 0.33 D) had better cor-relation with manifest refractive cylinder than manual keratometry (ORA 0.68 +/? 0.38 D), simulated keratometry (ORA 0.70 +/? 0.35 D), corneal wave-front (ORA 0.74 +/? 0.36 D) and paraxial curvature matching (ORA 0.85 +/? 0.48 D).. The ORAsd for CorT was significantly less than the other measures of astig-matism (p < 0.001). Conclusion: An alternative measure of corneal astig-matism, known as CorT, corresponds more closely to the manifest refractive cylinder than other measures of corneal astigmatism.