Quantitative analysis of posterior chamber morphology on vault after ICL implantation: a retrospective paired study

AIM: To quantitatively evaluate the influence of four posterior chamber morphological features—wide iris-ciliary angle (ICA), concave iris (CI), anteriorly positioned ciliary body (APCB), and ciliary body cyst (CBC)—on vault after implantable Collamer lens (ICL) implantation. METHODS: In this retrospective paired study, 925 eyes from 506 patients were analyzed. Participants were matched 1:1 based on ICL size, horizontal/vertical sulcus-to-sulcus (STS) diameters, and lens thickness. Posterior chamber morphology was assessed using ultrasound biomicroscopy (UBM). Actual vault measurements were compared against vault values predicted using the Zhu formula. Statistical analyses included paired t-tests and Bland-Altman agreement assessment. RESULTS: Eyes with wide ICA (n=82) and CI (n=26) exhibited significantly lower actual vault (mean difference: −137.93 and −145.00 μm, respectively; P<0.001) compared to controls. Conversely, the APCB group (n=77) showed higher vault (mean increase: 222.60 μm; P<0.001), while CBC (n=36) had no significant impact (P=0.054). Bland-Altman analysis revealed systematic prediction errors: wide ICA and CI groups had underestimated vault (mean bias: −165.4 and −175.0 μm), whereas APCB showed overestimation (mean bias: +212.4 μm). Notably, 31.71% of wide ICA and 36.36% of APCB cases exceeded prediction errors of ±300 μm. CONCLUSION: Posterior chamber morphology, particularly wide ICA, CI, and APCB, significantly affects postoperative vault. These features introduce systematic deviations in vault prediction, highlighting the need for integrating morphological parameters into ICL sizing algorithms to optimize surgical outcomes and reduce complications.