Comparison of Predictability in Vault using NK Formula and KS Formula for the Implantable Collamer Lens Surgery

Abstract Background The purpose of this study is to investigate the agreement of NK and KS formulas in predicting the vault after implantation of EVO-implantable collamer lens (ICL). Methods In this retrospective study, a total of 106 eyes of 59 patients who underwent ICL-V4c implantation were included. The predicted vault using the NK formula and the KS formula was provided by anterior segment optical coherence tomography (AS-OCT) automatically. The achieved vault was measured by AS-OCT at 1 month after surgery. Multivariate linear regression analyses were performed for evaluating correlations between postoperative vault and other biological parameters. Results The achieved vault was 604.34 ± 214.66 µm, which was significantly smaller than the predicted vaults of 713.50 ± 195.32 and 679.27 ± 211.00 µm, using the NK and KS formulas, respectively ( P < 0.05). The 95% limits of agreement of the achieved vault and the predicted vault using the KS formula were narrower than those of the achieved vault and the predicted vault using the NK formula in both ICL size groups. Anterior chamber depth (ACD) and sulcus-to-sulcus diameter (STS) were independent factors associated with achieved vault ( P < 0.05). It’s no significant difference in absolute prediction error (APE) between the two formulas. Conclusion There is no significant difference between the NK and KS formulas in terms of absolute predicted error vault. It should be noted that AS-OCT tended to overestimate the predicted ICL vault, particularly when selecting larger ICL sizes. ACD and STS were identified as potential crucial factors influencing the achieved vault.