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

Abstract

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.

In Brief

Keratometric astigmatism does not entirely account for refractive astigmatism in pseudophakes. Astigmatism from other factors, such as noncorneal astigmatism or perceptual preference, plays a significant role.