Comparison of magnitude and summated vector mean of surgically induced astigmatism vector according to incision site after phakic intraocular lens implantation

Kazutaka Kamiya; Wakako Ando; Masahide Takahashi; Nobuyuki Shoji

doi:10.1186/s40662-021-00257-z

Comparison of magnitude and summated vector mean of surgically induced astigmatism vector according to incision site after phakic intraocular lens implantation

Eye Vis (Lond). 2021 Sep 2;8(1):32. doi: 10.1186/s40662-021-00257-z.

Authors

Kazutaka Kamiya¹, Wakako Ando², Masahide Takahashi², Nobuyuki Shoji²

Affiliations

¹ Visual Physiology, School of Allied Health Sciences, Kitasato University, 1-15-1 Kitasato, Minami, Sagamihara, Kanagawa, 252-0373, Japan. kamiyak-tky@umin.ac.jp.
² Department of Ophthalmology, School of Medicine, Kitasato University, Sagamihara, Japan.

Abstract

Background: To compare the arithmetic mean (M-SIA) and the summated vector mean of surgically induced astigmatism (SVM-SIA) according to the incision site after phakic intraocular lens (Visian implantable collamer lens (ICL), STAAR Surgical) implantation.

Methods: This study comprised 121 eyes of 121 consecutive patients undergoing ICL surgery through a 3.0-mm temporal or superior clear corneal incision. The magnitude and the axis of corneal astigmatism preoperatively and 3 months postoperatively were measured using an automated keratometer. The M-SIA and the SVM-SIA were determined according to the incision site.

Results: The magnitude of corneal astigmatism significantly increased from 1.23 ± 0.59 D preoperatively to 1.46 ± 0.72 D postoperatively in the temporal incision group (Wilcoxon signed-rank test, P < 0.001), but it significantly decreased from 1.09 ± 0.36 D preoperatively to 0.86 ± 0.41 D postoperatively in the superior incision group (P < 0.001). The M-SIA was 0.48 ± 0.30 D, and the SVM-SIA was 0.23 ± 0.52 D at a meridian of 82° in the temporal incision group. The M-SIA was 0.57 ± 0.30 D, and the SVM-SIA was 0.47 ± 0.45 D at a meridian of 1° in the superior incision group.

Conclusions: ICL implantation induces the M-SIA by approximately 0.5 D, but the SVM-SIA decreased to 50% and 80% of the M-SIA in magnitude through temporal and superior incisions, respectively. The direction of the SVM-SIA showed a tendency toward corneal flattening to the incisional site. It should be noted that the M-SIA is somewhat different from the SVM-SIA according to the incision site. Trial registration University Hospital Medical Information Network Clinical Trial Registry (000044269).

Keywords: Centroid; Corneal astigmatism; ICL implantation; Mean; Summated vector mean; Superior incision; Surgically induced astigmatism; Temporal incision; Vector analysis.