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

Tomoya Nishida,1 Yukihito Kato,1,2 Yukihiro Sakai,1,2 Rie Horai,1,2 Satoshi Gotoda,1,2 Sho Ichikawa,1,2 Kei Ichikawa,1– 3 Kazuo Ichikawa1,21Department of Ophthalmology, Chukyo Eye Clinic, Nagoya, Aichi, Japan; 2Department of Ophthalmology, Grand Central Tower Tokyo Eye Clinic, Minato-ku, Tokyo, Japan; 3Department of Ophthalmology, Aoyama General Hospital, Toyokawa, Aichi, JapanCorrespondence: Tomoya Nishida, Department of Ophthalmology, Chukyo Eye Clinic, 12-22 Sanbonmatsu-cho, Atsuta-ku, Nagoya, Aichi, 456-0032, Japan, Tel +81-52-883-1543, Email nishida_tomoya@chukyogroup.jpPurpose: 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.Results: The derived formula was as follows: threshold (mm) = 0.9091 × preoperative AOD500 (mm) − 0.0493. In the CEC-implementation cohort, the formula yielded a sensitivity of 73.7% (14/19 eyes), specificity of 94.4% (135/143 eyes), and area under the receiver operating characteristic curve of 0.922 (95% confidence interval, 0.857– 0.972; P < 0.001). In the multivariable analysis, use of the threshold formula was associated with lower odds of postoperative narrow-angle classification (odds ratio, 0.311; 95% confidence interval, 0.138– 0.704; P = 0.005).Conclusion: An ICL sizing approach incorporating a preoperative angle-based threshold formula (the CEC method) was associated with a lower frequency of postoperative narrow-angle classification and warrants further prospective validation.Keywords: postoperative vault, narrow-angle classification, angle opening distance, anterior segment optical coherence tomography, phakic intraocular lens