Comparison of rotational stability of the Implantable Collamer Lens after using a vertical or horizontal implanting orientation

Purpose: To compare rotational stability of the Implantable Collamer Lens (ICL) between horizontal and vertical implantation. Setting: Zhongshan Ophthalmic Center, China. Design: Prospective 1:1 matched design. Methods: 94 cases (185 eyes with a vertical elliptical ciliary sulcus) were included with a 1:1 matched design based on ciliary sulcus morphology, preset deviation angle, and vault. Follow-ups at 4 days, 1 month, 3 months, and 6 months post-surgery measured rotational angles using slit-lamp photography. Latent class trajectory modeling was employed to investigate the postoperative rotational angle trajectories. Results: Six months after surgery, both groups exhibited similar visual acuity and refractive outcomes. The horizontal group had a significantly greater rotation angle than the vertical group (F group = 13.638, P < 0.001). Additionally, a statistically significant difference ( P = 0.004) in the average trajectories of rotational angles was observed. The vertical group displayed a greater presence in the low-stable trajectory subgroup while demonstrating a reduced presence in the moderate-increase and high-fluctuation trajectory subgroups compared to the horizontal group. The horizontal group had a 3.750 times higher risk of rotation angle ≥3° compared to the vertical group, which represented a statistically significant difference (95% CI: 1.346∼10.446). In both groups, a positive correlation between the preset deviation angle and the rotation angle was observed, with correlation coefficients of 0.320 ( P = 0.030) and 0.371 ( P = 0.011), respectively. Conclusions: Vertical ICL implantation showed better rotational stability than horizontal implantation in eyes with a vertical elliptical ciliary sulcus, offering guidance for ICL surgery.