One hundred forty-nine eyes of 124 consecutive cases scheduled for simple cataract surgery at the Osaka University Hospital were included in this retrospective case series. Subjects who required other ocular surgeries such as vitreoretinal surgery or a glaucoma surgery were excluded. The research adhered to the tenets of the Declaration of Helsinki. The institutional review board of Osaka University Hospital approved this study. All participants provided informed consent after the purpose of the study and the procedures were explained.

Corneal topographic analysis was performed using the KR-9000PW (Topcon Corporation, Tokyo, Japan). Two corneal specialists performed visual inspection of color-coded axial power maps with Smolek/Klyce 1.5 diopter (D) power step. Measurements were repeated at least twice to confirm the reproducibility of the topographic maps, and the better map was selected. When appearances of the topographic maps were not reproducible due to poor fixation, head movement, or other reasons, or if the measured area was smaller than 6-mm diameter due to narrow fissure and so on, data was considered as unreliable. Age, gender, and the preoperative distance spectacle-corrected visual acuity (DCVA) of those eyes for which reliable data for the central 6 mm of the cornea were not obtained were compared to those with reliable data.

Four parameters associated with the corneal optical characteristics, i.e., corneal total higher-order aberrations (HOAs), the differences between the central corneal power and simulated K readings (ΔK), the corneal spherical aberration (Z40), and the corneal cylinder, were recorded. Corneal HOA was calculated from the topographic data quantitatively as a set of coefficients of the Zernike polynomials up to the 6th order, and root mean square (RMS, μm) values were used. The total HOAs for the 4-mm corneal diameter were selected to evaluate the clinically relevant corneal irregular astigmatism. Because the blurring effect of 0.5 D defocus corresponds to the RMS value of 0.29 μm for 4-mm diameter, corneal irregular astigmatism was considered to be clinically relevant when the total HOAs exceeded 0.3 μm.

The ΔK was used to determine an abnormal corneal shape that might increase the postoperative refractive error because of inadequate K readings with conventional keratometry when calculating the IOL power [9–12]. A ΔK 0.5 D was considered abnormal value because most of the IOLs were prepared with 0.5 D steps. The Z40 for a 6-mm corneal diameter was chosen to indicate the corneal asphericity. This is because aspherical IOLs show better visual performance than spherical IOLs especially under mesopic conditions and also the asphericity of aspherical IOLs was shown for Z40 for 6-mm diameter [13–15]. A Z40 below 0.1 μm was considered to be an abnormal value because aspherical IOLs with Z40 of −0.20 μm will increase the absolute value of Z40. The optical quality might be reduced due to negative spherical aberration in such cases [16]. Corneal cylinder exceeding 1.5 D was selected as the cutoff value since these eyes were not a good indication for multifocal IOLs but a better indication of surgery for astigmatic correction, such as limbal relaxing incisions (LRIs), touch-up with laser in situ keratomileusis (LASIK), or a toric IOL.