Anterior, posterior, and nonkeratometric contributions to refractive astigmatism in pseudophakes

Purpose: To investigate the relationship between measured anterior (ACA) and posterior (PCA) keratometric astigmatism and postoperative refractive astigmatism (RA) and to quantify noncorneal astigmatism (NCA) contributions to RA. Setting: Penn State College of Medicine, Hershey, Pennsylvania, USA. Design: Retrospective consecutive case series. Methods: Consecutive eyes underwent preoperative biometry (IOLMaster 700) and tomography/topography using a dual Scheimpflug–placido disk–based device (Galilei G4), cataract surgery with implantation of a monofocal intraocular lens (IOL), and postoperative manifest refractions. RA was compared with keratometric astigmatism using the following methods: IOLMaster, SimK, CorT, SimK + measured PCA, total corneal power at the corneal plane (TCP2), and CorT(Total). An ocular residual astigmatism (ORA) vector was calculated between RA and each measured astigmatism. Results: Analysis was based on 296 eyes. ORA centroids were 0.28 @ 179, 0.45 @ 001, 0.37 @ 001, 0.19 @ 003, 0.19 @ 001, and 0.23 @ 178 diopter (D) for the 6 aforementioned methods, respectively (P < .000001 [ORAx, ORAy]). Based on TCP2 measurements, eyes with against-the-rule ACA and with-the-rule (WTR) ACA had ORA centroids of 0.09 @ 082 and 0.58 @ 001 D (P < .000001 [ORAx, ORAy]), respectively. ORA was nonzero and not entirely explained by the cornea, especially in those with WTR ACA. Conclusions: Total keratometric astigmatism did not explain all ocular astigmatism. Noncorneal contributions were significant, especially in eyes with WTR ACA.