Background <p>To compare the accuracy of toric intraocular lens (IOL) calculation using simulated keratometry (SimK) obtained from two different devices in cataract eyes with central or paracentral preoperative corneal irregular astigmatism.</p> Methods <p>Patients with cataract and irregular preoperative corneal astigmatism who underwent uneventful cataract phacoemulsification with toric IOL implantation were retrospectively enrolled. Irregular preoperative corneal astigmatism was confirmed by corneal topography. SimK was obtained using swept-source optical biometry (IOLMaster700, SimK_M) and Scheimpflug photography (Pentacam HR, SimK_P). Eyes were divided into central (within 3-mm zone) and paracentral (3 to 7-mm zone) irregular astigmatism groups, with subgroup analyses performed accordingly.</p> Results <p>A total of 111 eyes (92 patients) were included, including 52 eyes with central and 59 eyes with paracentral irregular astigmatism. Postoperative astigmatism significantly decreased in both groups (both <i>P</i> &lt; .01). Patients in the central irregular astigmatism group had significantly greater postoperative refractive astigmatism than those in the paracentral group. Comparison of SimK-based predictions between the two devices revealed that K_M had lower postoperative refractive astigmatism prediction error in the central irregular astigmatism group.</p> Conclusions <p>Toric IOL implantation effectively reduces corneal irregular astigmatism. SimK obtained from optical biometry (IOLMaster 700) demonstrated superior accuracy in predicting postoperative refractive astigmatism compared to Scheimpflug topography (Pentacam HR) in eyes with central irregular astigmatism; this advantage was not observed in paracentral irregularity and should not be generalized to all irregular corneas.</p>