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Development and Clinical Evaluation of an Anterior Chamber Angle-Based Lens Sizing Method for Implantable Collamer
Tomoya Nishida1, Yukihito Kato1,2, Yukihiro Sakai1,2
1Department of Ophthalmology, Chukyo Eye Clinic, Nagoya, Aichi, Japan.
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.
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.