Development and Clinical Evaluation of an Anterior Chamber Angle–Based Lens Sizing Method for Implantable Collamer Lens Surgery

Purpose

To derive a regression formula estimating an individualized postoperative vault threshold associated with narrow-angle status from preoperative angle measurements and to evaluate an implantable collamer lens (ICL) sizing approach incorporating this formula. Patients and Methods: This retrospective study included a formula-derivation cohort of 97 eyes treated from April 2024 to March 2025 and a CEC-implementation cohort of 162 eyes treated from April 2025 to March 2026. The 360° angle opening distance at 500 μm (AOD500) was measured by anterior segment optical coherence tomography (AS-OCT; CASIA2, TOMEY). Postoperative angle status was classified by the device’s Narrow Angle Index (NAI) software. Eyes open in all 32 radial directions formed the open group; those narrow or closed in at least one direction formed the narrow group. A threshold formula was derived from the relationship between preoperative AOD500 and postoperative vault among the 29 narrow-group eyes of the derivation cohort. In the CEC-implementation cohort, the formula’s discrimination of postoperative angle status was assessed, and its association with postoperative narrow-angle classification was examined using multivariable logistic regression with generalized estimating equations. The threshold formula was used alongside the KS and NK formulas and a previously reported equation for predicting postoperative trabecular-iris angle (post-TIA) to select a lens size with a predicted vault below the calculated threshold.