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

Area of Science:

• Ophthalmology
• Biomedical Engineering
• Optical Engineering

Background:

• Implantable collamer lenses (ICLs) are used for refractive error correction.
• Accurate prediction of postoperative vault is crucial for ICL safety and efficacy.
• The NK and KS formulas are commonly used to predict vault, but their agreement needs investigation.

Purpose of the Study:

• To investigate the agreement between the NK and KS formulas in predicting the postoperative vault after EVO-ICL implantation.
• To compare the predictive accuracy of the NK and KS formulas.
• To identify factors influencing achieved vault post-ICL surgery.

Main Methods:

• Retrospective study of 106 eyes (57 patients) undergoing EVO-ICL-V4c implantation.
• Preoperative vault prediction using NK and KS formulas.
• Postoperative vault measurement using anterior segment optical coherence tomography (AS-OCT) at one month.
• Analysis of vault prediction accuracy and correlation with biometric parameters.

Main Results:

• Achieved vaults were significantly smaller than predicted by both NK and KS formulas (P < 0.05).
• Mean differences between achieved and predicted vaults were -104.82 µm (NK) and -68.55 µm (KS).
• Anterior chamber depth, V-STS diameter, and CLR were associated with achieved vault; no significant difference in absolute prediction error between formulas.

Conclusions:

• The NK formula showed better consistency than the KS formula for the 12.6 mm ICL size.
• AS-OCT measurements overestimated predicted ICL vault, particularly with 13.2 mm ICLs.
• Sole reliance on NK or KS formulas for preoperative vault prediction is not advised.