From ciliary sulcus asymmetry to vault prediction: an hSTS-based approach to individualized sizing of implantable collamer lenses in myopic eyes

Objective To investigate the distribution and correlations of horizontal and vertical sulcus-to-sulcus diameters (hSTS/vSTS) in myopic eyes with different refractive errors, and to develop a predictive model for postoperative vault after posterior chamber phakic implantable collamer lens (ICL) implantation based on key anterior segment parameters. Methods This retrospective study included two non-overlapping cohorts of myopic patients who underwent ICL implantation at a single tertiary eye hospital. The morphology cohort comprised 244 eyes, classified into moderate, high, and extreme myopia groups according to spherical equivalent (SE). Ultrasound biomicroscopy (UBM) was used to measure hSTS and vSTS; inter-group comparisons and correlation analyses were performed. The model development cohort included 44 patients (72 eyes). In addition to STS, preoperative anterior segment parameters (corneal curvature, horizontal corneal diameter, anterior chamber depth, lens thickness, and axial length) were recorded, and ICL size was selected according to the STAAR nomogram. One month postoperatively, the vault was measured using anterior segment optical coherence tomography. Univariate correlation and stepwise multiple linear regression were applied to identify factors and derive a prediction formula. Results The ciliary sulcus was predominantly vertically elliptical in the overall population (vSTS hSTS). In the extreme myopia group, both hSTS and vSTS were significantly larger than in moderate and high myopia groups, with a greater vSTS-hSTS difference (0.63 ± 0.38 mm, all P 0.05). SE correlated weakly and negatively with hSTS ( r = –0.177, P = 0.006) and vSTS ( r = –0.243, P 0.001), while hSTS and vSTS were strongly positively correlated ( r = 0.781, P 0.001). In the modeling cohort, stepwise regression identified hSTS and ICL size as independent predictors of vault (adjusted R 2 = 0.657), yielding the formula: vault (μm) = –2286.216 - 164.416 × hSTS (mm) + 375.487 × ICL size. Conclusion The higher myopic refractive error is associated with a more pronounced vertically elliptical ciliary sulcus. Routine measurement of both vertical and horizontal STS, combined with a vault prediction model based on hSTS and ICL size, may facilitate individualized ICL sizing, improve vault predictability, and enhance surgical safety.