Short- and Long-Term Dynamics of Endothelial Cell Density and Vault Changes After Implantable Collamer Lens Implantation

Background/Objectives: Endothelial cell density (ECD) and vault height are essential safety metrics in implantable collamer lens (ICL) surgery, yet their reported decay rates vary. This study assessed short- and long-term changes in ECD and vault height. Methods: Medical records of patients undergoing V4c ICL implantation between 2014 and 2024 were reviewed. ECD loss was evaluated across three periods: early (baseline to 6 months), late (6 months to last visit), and total (baseline to last visit). Vault was measured at day 1 and months 3, 6, 12, and the last visit and decay rate was calculated for the entire follow-up period. Results: A total of 631 eyes of 323 patients were analyzed. The early, late, and total ECD losses per year were 1.81 ± 8.56% (95% CI 0.43 to 3.19), 0.68 ± 2.11% (95% CI 0.34 to 1.03), and 1.21 ± 2.58% (95% CI 0.83 to 1.59), respectively. The ECD loss rate was not correlated with vault. Vault decreased rapidly during the first 3 postoperative months (−178.0 µm/year; 95% CI, −211.4 to −144.6; p < 0.001), followed by a substantially slower but still significant decline (−19.1 µm/year; 95% CI, −23.9 to −14.2; p < 0.001). The difference between the early and late slopes was significant (p < 0.001). The vault decay rate was 6.80 ± 10.41% (95% CI, 5.48 to 8.13%) per year and was not associated with ICL size or anterior chamber depth. Conclusions: ECD loss was greatest and most variable during the first 6 months postoperatively. Thereafter, a slower sustained decline was observed. Vault decay showed a biphasic pattern, with a relatively rapid decrease during the first 3 postoperative months and a significantly slower long-term decline.