ICL – TECHNICAL PRECISION
This page is for patients preparing for ICL surgery who want to understand how the implant is sized, what vault means, why it matters, and how surgeons ensure it is correct.
Vault Is the Single Most Important Measurement After ICL
In Mr Hove’s 2024-2025 series, 100% of vault measurements at one week were within the safe range. Vault is the distance between the posterior surface of the ICL and the anterior surface of the natural crystalline lens. It is measured using anterior segment OCT, a non-contact imaging technology that provides a cross-sectional view of the anterior chamber with micron-level precision.³ The target vault range at Blue Fin Vision® is 250-750 microns, the window within which the ICL provides correction without creating risk at either end of the spectrum.
Too low: if vault falls below 150-200 microns, the ICL makes contact with or compresses the crystalline lens. Prolonged contact causes anterior subcapsular opacity, the mechanism by which ICL can, if improperly sized or inadequately monitored, cause cataract.² This is the primary safety risk of ICL and the primary reason vault monitoring is mandatory for life.
Too high: if vault is above 750-1000 microns, the ICL touches the iris, potentially obstructing aqueous flow and raising intraocular pressure. Elevated IOP damages the optic nerve.⁴ This is managed by reduction in ICL size or addition of peripheral iridotomy in affected patients.
How ICL Size Is Predicted
ICL sizing is not guesswork. The implant size is selected using a formula incorporating three measurements: anterior chamber depth (ACD, the distance from the corneal endothelium to the front of the natural lens), white-to-white diameter (WTW, the horizontal diameter of the visible iris), and sulcus-to-sulcus distance (STS, the distance between the ciliary sulci where the ICL footplates rest, estimated by formula when direct measurement is not available).¹
Modern sizing formulas, including the Okulix and manufacturer-provided calculators, predict vault within the safe range in the majority of cases. Sizing accuracy has improved substantially with the adoption of anterior segment OCT-based ACD measurement over older pachymetry-based estimates.
What Happens If Vault Is Outside the Target Range
Vault outside the safe range at the post-operative reviews is identified early through the structured monitoring schedule. If vault is low: ICL exchange for a larger implant is the standard management, the lens is replaced in a brief outpatient procedure. If vault is high: a smaller ICL is implanted, or peripheral iridotomy is performed to protect aqueous drainage. Both interventions are straightforward when vault drift is identified at the one-week or one-month review rather than years later.
Clinical Perspective
Mr Mfazo Hove, ICL surgeon at Blue Fin Vision®, measures ACD using anterior segment OCT at every ICL pre-operative assessment, reviews all sizing calculations personally, and targets vault to the 250-750 micron range. In our 2024-2025 ICL series, 100% of vault measurements at the one-week review were within the safe range, and no patient required unplanned ICL exchange within twelve months of surgery. This reflects sizing accuracy built across years of consecutive ICL implantation, not a formula applied without clinical judgement.
Clinical Takeaway
ICL vault, the gap between the implant and the natural lens, is the primary safety measurement post-ICL. The target range is 250-750 microns. Vault is determined pre-operatively by anterior chamber depth, white-to-white diameter, and sulcus-to-sulcus estimation. At Blue Fin Vision®, 100% of vault measurements in the 2024-2025 series were within the safe range at one week. Annual monitoring maintains that record for life. If you have had ICL surgery elsewhere and have not had a vault check in over twelve months, book an OCT vault review at Blue Fin Vision®.
References
- Rosen E, Gore C. Staar Collamer posterior chamber phakic intraocular lens to correct myopia and hyperopia. J Cataract Refract Surg. 1998;24(5):596-606.
- Trindade F, Pereira F. Cataract formation after posterior chamber phakic intraocular lens implantation. J Cataract Refract Surg. 1998;24(12):1661-3.
- Baikoff G. Anterior segment OCT and phakic intraocular lenses: a perspective. J Cataract Refract Surg. 2006;32(11):1827-35.
- Kohnen T, Kook D, Morral M, Guell JL. Phakic intraocular lenses: part 2, results and complications. J Cataract Refract Surg. 2010;36(12):2168-94.
- Gierek-Ciaciura S, Gierek-Lapinska A, Ochalik K, Mrukwa-Kominek E. Correction of high myopia with different phakic anterior chamber intraocular lenses. Graefes Arch Clin Exp Ophthalmol. 2007;245(1):1-7.
