Horizontal Versus Vertical Sulcus-To-Sulcus Measurements: Anatomical Asymmetry And Determinants Of Postoperative Vault

To compare horizontal (H) and vertical (V) sulcus-to-sulcus (STS) and crystalline lens rise (CLR) measurements, evaluate their agreement and interchangeability, and determine their relationship with postoperative vault and implant orientation in EVO ICL surgery.

Prospective observation study in one single clinical site 

30 eyes from 30 patients were included. H and V measurements were obtained by UBM. Agreement between H and V STS measurements was assessed using Bland–Altman analysis, including estimation of mean bias and 95% limits of agreement. Proportional bias was evaluated by linear regression of differences(H−V) against the mean value. Intraclass correlation coefficient (ICC) was calculated using a two-way random-effects model for absolute agreement

Axis-specific CLR and postoperative vault were analyzed similarly. A multivariate linear regression model was constructed to identify independent determinants of postoperative vault, including CLR at implantation, effective compression (ICLsize−STS), and implant orientation

Mean H STS was 12.13±0.37mm and V STS was 12.51±0.41mm, with a mean difference of −0.37±0.24mm. Bland–Altman analysis demonstrated a systematic bias. The ICC was moderate (0.56; 95% CI −0.10 to 0.84), with wide uncertainty.

H CLR was consistently lower than V CLR (mean difference approx −90 µm).

Mean postoperative vault differed between orientations (444.8±181.5 µm H vs 390.8±140.0 µm V; mean difference 54.1±63.9 µm).

In multivariate analysis (R²=0.50; model p=0.017), higher CLR was independently associated with lower vault (β=−0.57 µm/µm; p=0.0029), and greater effective compression was independently associated with higher vault (β=+331 µm/mm; p=0.040). Implant orientation was not an independent determinant of vault(p=0.51).

Vertical STS measurements are consistently greater than horizontal STS, confirming clinically relevant anatomical asymmetry of the ciliary sulcus. The CLR measured along the vertical axis was systematically greater than along the horizontal axis, reflecting axis-dependent anatomical asymmetry.

Postoperative vault appears primarily driven by anatomical factors, particularly CLR and effective compression, rather than implant orientation itself. Implant orientation acts as a surrogate of underlying axis-specific anatomy rather than an independent biomechanical determinant.

These findings support the importance of axis-specific anatomical assessment when planning ICL implantation to improve vault predictability.