Evaluation of Optimised Implantable Collamer Lens Sizing using an Optical Low-Coherence Reflectometry Biometry Device at 12 months follow up

PURPOSE: Implantable Collamer Lens (ICL) surgery can treat ametropia when laser vision correction is not suitable. Lens sizing is important to prevent insufficient or excessive vaulting. The Online Calculator and Ordering System (OCOS) requires an 'optimised' value for white-to-white (WTW) values when using the IOLMASTER or LENSTAR 900 (LS900) for biometry. We assessed if a more specific WTW subtraction for the LS900 could improve sizing outcomes. SETTINGS: Single-centre London private practice setting. DESIGN: A retrospective observational cohort study of consecutive patients undergoing ICL surgery within a 4-year period. METHODS: Pre-operative measurements were taken using the LS900 and lenses were sized using the OCOS calculator with a WTW subtraction of 0.4mm. Vault height was measured at 2 weeks, 3 months and 12 months and complications recorded. Simulations were run using a more tailor-made subtraction of 0.25mm for the LS900. RESULTS: 199 eyes from 102 patients were analysed. 'Ideal' sizing occurred in 70% of ICLs at 3 months and dropped to 67% at 12 months. The largest proportion of incorrectly sized lenses were oversized at 3 months but undersized at 12 months. Simulations using an alternative WTW subtraction of 0.25mm suggest a redistribution of vault heights away from undersizing at 12 months when LS900 biometry is used. CONCLUSION: Oversizing of ICLs using the OCOS calculator may be due to measurement discrepancies and early post-operative measurements of vault height. An alternative WTW subtraction of 0.25mm may reduce exposure to low vaults, which are a known risk factor for cataract formation. Real-world evaluation of this subtraction would be needed to confirm an improvement in accuracy.