Toric IOL rotation appears to be greater in longer eyes

This prospective study published in January in the Journal of Cataract & Refractive Surgery evaluated the effect of axial length on the rotational stability of the AcrySof toric IOL. The results demonstrate greater rotation in eyes with longer axial length, regardless of IOL alignment in the capsular bag. However, the authors say the clinical significance of this association between increasing axial length and IOL rotation remains uncertain.

Subjects were 168 patients (168 eyes) who underwent AcrySof toric IOL implantation. The authors measured axial length using optical coherence biometry or immersion A-scan biometry, and corneal astigmatism by manual keratometry and topography. They measured rotational stability using a software-based technique with a purpose-designed grid that they developed. They found that their software was accurate and easy to use, providing precise and reproducible IOL rotation measurements.

Mean axial length was 23.86 mm ± 1.63 (SD; range, 19.50 to 29.03 mm). The median IOL rotation was 0.3 degree from baseline to one week, 1.0 degree from one week to one month, 0.2 degree from one to three months and 0.1 degree from three to six months. The maximum rotation occurred between one week and one month. There was a strong correlation between axial length and IOL rotation at six months (P < 0.001). However, the mean absolute difference at six months was not significantly different between horizontal, vertical and oblique axis placements when correlated with rotation (P = 0.102).

The maximum IOL rotation measured in myopic eyes was three degrees, with a correlation between high axial length and a three-degree IOL rotation. The authors say that factors such as slight tilting of the head and errors in measuring keratometry or topography may contribute to imprecise alignment. Therefore, they are unable to determine whether the one to three degrees of postoperative rotation observed is clinically significant.