Simulation of toric intraocular lens results: manual keratometry versus dual-zone automated keratometry from an integrated biometer. 
To evaluate simulated clinical outcomes in patients with toric intraocular lenses (IOLs) calculated on the basis of dual-zone automated keratometry from an integrated optical biometer, relative to manual keratometry.  Private practice, Mesa, Arizona, USA.  Comparative case series.  Patient records at 4 clinical sites were reviewed to identify patients who had manual keratometry and biometry with the Lenstar LS 900 recorded before toric IOL implantation and refractive follow-up data after implantation.  Preoperative and operative data were extracted from patient charts.  Simulated refractive outcomes were calculated based on mathematically removing the actual IOL implanted and then mathematically inserting the IOLs as determined by manual or automated keratometry from the biometry device.  Data for 128 patients were available for analysis.  The actual residual astigmatism was comparable between manual keratometry and automated keratometry from the biometry system.  Although simulated residual refractive astigmatism was similar between the 2 devices on average, there was variability in results by patient.  Simulated residual refractive astigmatism was lower for the biometer when the standard deviation of the angle of astigmatism was low.  Site-to-site variability was lower with the biometer than with manual keratometry.  Simulated outcomes suggest that overall results for a group of patients whose toric IOL surgery planning is performed with the dual-zone automated keratometry data from the biometer will be equivalent to those when manual keratometry is used.  The reduced site-to-site variability with the biometer suggests an operational advantage.