Effect of implantable collamer lens on biometric measurements and intraocular lens power calculation formulas.

Abstract

Objective: To investigate the effect of the implantable collamer lens (ICL) on biometric measurements and intraocular lens (IOL) power calculation formulas.

Methods: This prospective theoretical study included 92 eyes undergoing ICL surgery. Preoperative and 1-year postoperative biometric parameters, including axial length (AL), keratometry (K), anterior-chamber depth (ACD), lens thickness (LT), central corneal thickness (CCT) and corneal diameter (CD), were measured using IOLMaster 700. Nine formula types (10 variants) were evaluated: Barrett Universal II (BU II; BU II^a, IOLMaster 700-based; BU II^b, online calculator), Cooke K6, EVO, Hill-RBF, Hoffer QST, Holladay 1, Kane, Pearl-DGS and SRK/T. Primary outcomes were the difference in predicted spherical equivalent before and after ICL implantation (Δ-pSEQ) and the percentage of eyes within specified Δ-pSEQ ranges.

Results: For all eyes (n = 92), significant post-ICL changes included increased AL, steep K (K2), LT, CCT (+0.02 mm, +0.08 D, +0.26 mm, +0.003 mm; p = 0.031, 0.021, <0.001, 0.008) and decreased ACD (-0.28 mm, p < 0.001). ACD segmentation errors occurred in 34.78% of eyes, associated with low vault (optimal cut-off, 0.491 mm; AUC = 0.921). Eyes were grouped by segmentation accuracy (correct, n = 60; incorrect, n = 32). All Δ-pSEQ values were within ±0.50 D; between-subgroup differences in Δ-pSEQ ranges were not significant (p > 0.05). The highest proportions within ±0.25 D were SRK/T (86% overall, 94% incorrect group) and BU II^a (85% correct group); EVO had the lowest (71%-72%).

Conclusion: ICL implantation alters biometric measurements and theoretically predicted Δ-pSEQ; although these changes are statistically significant, their clinical significance is negligible. While incorrect ACD segmentation is common, it is unlikely to substantially affect the theoretical calculation results.