Comparative study on rotational stability of toric intraocular lenses in cataract patients with low astigmatism: vertical versus horizontal implantation.

Objective

To compare the effects of horizontal versus vertical in-the-bag implantation of toric intraocular lenses (IOLs) on postoperative rotational stability, refractive outcome, and vision-related quality of life in cataract patients with low regular astigmatism, and to identify risk factors for postoperative rotational instability.

Methods

This retrospective study included 370 eyes of 370 patients with low regular astigmatism who underwent phacoemulsification with toric IOL implantation. Patients were divided into horizontal implantation (n = 189) and vertical implantation (n = 181) groups according to intraoperative IOL orientation. Follow-up assessments were conducted at 1 week, 1 month, and 3 months postoperatively. The primary outcome was rotational instability at 3 months, defined as a rotation angle ≥ 5°. Secondary outcomes included rotation angle over time, uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), spherical equivalent (SE), residual astigmatism, and National Eye Institute Visual Function Questionnaire-25 (NEI VFQ-25) scores. Longitudinal changes were analyzed using a linear mixed-effects model (LMM), and logistic regression was used to identify risk factors.

Results

Baseline and intraoperative data were comparable between groups. The LMM revealed significant effects of time, group, and their interaction on rotation angle (all P < 0.001). Rotation angles were significantly lower in the vertical implantation group than in the horizontal implantation group at all follow-up time points (all P < 0.001). At 3 months, rotational instability was lower in the vertical group than in the horizontal group (5.5% vs. 16.9%, P < 0.001). The vertical group demonstrated better UCVA, BCVA, SE, and lower residual astigmatism (all P ≤ 0.001), along with higher NEI VFQ-25 scores across multiple domains. Vertical implantation was independently protective (OR = 0.194, 95% CI: 0.077-0.444, P < 0.001), whereas longer axial length, shallower anterior chamber depth, and larger capsular bag diameter were identified as risk factors. Complication rates were similar between groups.

Conclusion

Vertical in-the-bag implantation of toric IOLs provided superior rotational stability, refractive outcomes, visual recovery, and vision-related quality of life compared to horizontal implantation in cataract patients with low regular astigmatism.