Accurate Sizing and Suitability of an Implantable Collamer Lens (ICL)
- Posted
- Medically Reviewed by Mr Mfazo Hove Consultant Ophthalmologist
- Author: Chris Dunnington
- Published: October 31, 2025
- Last Updated: November 12, 2025
When it comes to correcting vision through Implantable Collamer Lenses (ICLs), precision is paramount. At Blue Fin Vision®, a top-rated private eye clinic with locations across London, Chelmsford, and Hatfield, we understand that every detail matters. This is why our leading surgeons, and top specialists prioritise the accurate sizing and suitability of ICLs to ensure each patient receives the safest, most effective treatment tailored to their unique eyes.
Why Accurate ICL Sizing Is So Crucial
An Implantable Collamer Lens is no ordinary lens. It is placed in the posterior chamber, sitting delicately behind the iris and in front of the crystalline lens. Because of its precise placement within the eye’s anatomy, the sizing of the ICL is critical. A lens that is too large or too small can lead to complications that affect vision and eye health.
Possible complications include:
- High vault: where the lens sits too far from the natural lens, potentially causing angle closure, pigment dispersion, or pupillary block.
- Low vault: where the lens contacts the crystalline lens, raising the risk of cataract development.
Our top doctors at Blue Fin Vision® leave nothing to chance. We employ state-of-the-art diagnostic tools and proven measurement techniques to prevent such outcomes and secure optimal results.
Essential Ocular Measurements for Precise ICL Sizing
To accurately size an ICL, various ocular parameters must be measured with care and expertise. Blue Fin Vision® uses advanced imaging and biometric technology to capture every necessary detail:
Sulcus-to-Sulcus (STS) Diameter
This is the gold standard measurement for ICL sizing and the most direct indication of where the lens haptics will rest within the eye. STS measures the internal diameter of the ciliary sulcus, the true anatomical space for the lens.
- Measured by: Ultrasound Biomicroscopy (UBM) such as the Quantel Aviso and ArcScan Insight 100, or anterior segment Optical Coherence Tomography (OCT) devices including the Heidelberg Anterion, Zeiss Visante, and Tomey CASIA2.
- Importance: The width of the sulcus directly influences ICL vault and fit.
- Typical range: 11.0 to 12.5 mm.
STS measurement provides more precise sizing than external measurements such as White-to-White and is available at all Blue Fin Vision® locations.
Anterior Chamber Depth (ACD)
ACD measures the distance from the corneal endothelium to the front of the natural crystalline lens.
- Minimum safe depth: Generally accepted as 2.8 mm (some experts accept 2.6 mm).
- Why it matters: Shallow chamber depth increases the risk of crowding inside the eye and affects vault behaviour.
- Measured by: Optical biometry tools like IOLMaster 700, Lenstar LS900, and Scheimpflug or OCT imaging systems such as Pentacam, Anterion, Revo FC, and CASIA 2.
Crystalline Lens Rise (CLR)
CLR assesses how much the natural lens protrudes anteriorly relative to the sulcus line.
- Significance: A higher lens rise means the vault will be smaller for a given lens size, critical for predicting post-operative vault success.
- Typical range: 100 to 700 microns; a rise above 600 microns usually suggests a smaller ICL for safety.
- Measured by: Anterior segment OCT devices such as Anterion, Revo FC, and CASIA 2.
White-to-White (WTW) Diameter
WTW measures the visible corneal diameter from limbus to limbus.
- Role: Traditionally used as a proxy for the sulcus diameter but only moderately correlates (r approximately 0.5 to 0.6).
- Limitations: Influenced by factors like ethnicity, corneal curvature, and iris configuration.
- Measured by: Optical biometers including IOLMaster 700, Pentacam AXL, and Topcon Aladdin.
Anterior Chamber Width (Angle-to-Angle, ATA)
ATA measures the distance between the angle recesses, providing a reproducible and closer correlate to the sulcus diameter than WTW.
- Why important: More reproducible than WTW and correlates better with STS (r ≈ 0.8).
- Increasingly used: In modern nomograms for improved lens sizing.
- Measured by: OCT or Scheimpflug systems like Anterion, CASIA 2, and Revo FC.
Additional Metrics for Fine-Tuning
- Lens Thickness (LT): Thicker lenses can lower vault height and affect vault prediction. Measured via OCT or biometry.
- Corneal Curvature (K): Affects the effective optical zone with minor vault impact.
- Axial Length (AL): Useful for assessing overall eye size when combined with lens curvature.
- Pupil Size: Larger pupils risk edge glare if the ICL is undersized optically.
Important Considerations for Hyperopes: Laser Peripheral Iridotomy
For hyperopes (patients with far-sightedness), a laser peripheral iridotomy is required prior to ICL insertion. This procedure creates a tiny opening in the peripheral iris to prevent angle closure by allowing fluid flow within the eye. Blue Fin Vision® carries out this laser peripheral iridotomy as part of the ICL surgery package, with no additional charge to patients. This inclusion demonstrates our commitment to comprehensive care and patient reassurance.
Leveraging Advanced Technology and AI for Precision
Our top specialists utilise modern vault prediction nomograms that combine these biometric parameters for the most accurate lens sizing possible. These calculators may incorporate:
- Common nomograms: WTW + ACD (STAAR EVO+ Online Calculator), WTW + ACD + CLR (Nakamura modification), ATA + CLR (Benavente/Kojima formula).
- Advanced AI tools: Machine-learning models integrated into devices like the Revo FC Vault AI and Anterion AI module incorporate parameters such as ACD, ATA, CLR, lens thickness, and horizontal visible iris diameter (HVID), providing highly personalised sizing guidance.
Using these cutting-edge tools ensures each patient receives an ICL perfectly sized for their eyes, offering the best chance of clear, comfortable vision with minimal risk of complications.
Optimal Vault: The Goldilocks Zone
Post-implant vault – the space between the ICL and the crystalline lens – is a critical indicator of success.
- Optimal range: Between 250 and 750 microns.
- Too low (below 200 microns): Risk of lens contact and cataract formation.
- Too high (above 1,000 microns): Risks include angle closure or pigment dispersion.
Our expert surgeons at Blue Fin Vision® measure vault post-operatively with precision OCT imaging, ensuring your lens sits just right.
Why Choose Blue Fin Vision® for Your ICL Procedure?
At Blue Fin Vision®, our reputation as a top-rated private eye clinic in London, Chelmsford, and Hatfield reflects our unwavering commitment to excellence. Patients can expect:
- A team of leading surgeons and top specialists dedicated to personalised care
- Utilisation of the latest diagnostic equipment and surgical technology
- Access to a network of specialist clinics offering convenient locations without compromising expertise
- Consistent, surgeon-led care that ensures the same high standards wherever you are treated
- A trusted clinic endorsed by both patients and industry authorities alike
Our patient-first ethos means no detail is overlooked, and every step is tailored to your needs, from initial consultation through to recovery.
Clarity Restored Overnight
This extraordinary Blue Fin Vision® patient journey captures what sets our clinic apart: just 24 hours after Implantable Collamer Lens (ICL) surgery, she transitioned from a -7 prescription – unable even to see the largest chart letter unaided – to an outstanding 6/5 vision level. With bright, clear eyes and not a hint of redness, she confidently attended a black tie dinner the very next evening with no glasses or contact lenses.
The anterior segment OCT images confirm her ICL vault is in the Goldilocks zone (250–750 μm above the crystalline lens), demonstrating optimal lens positioning and safety.
Our unwavering commitment to lifetime eye health means all patients receive annual ICL vault and endothelial cell count checks, with comprehensive results delivered for their records every year as part of our inclusive Blue Fin Vision® aftercare package – so you’re always confidently protected by expert monitoring.
Trust Your Vision to Blue Fin Vision®
For those considering Implantable Collamer Lens surgery, precision and personalised expertise are non-negotiable. Blue Fin Vision® offers comprehensive assessments incorporating all essential biometric measurements using cutting-edge technology. This results in safer, more predictable outcomes and the exceptional care you deserve.
If you’re in London, Essex, or Hertfordshire, why settle for anything less than the very best?
Book your consultation today at the Blue Fin Vision® clinic most convenient to you and take the first step towards clear, confident vision with the support of trusted experts, state-of-the-art technology, and a team that truly understands the value of your sight. Your eyes deserve nothing less.
By choosing Blue Fin Vision®, you partner with a top-rated private eye clinic driven by expertise, precision, and compassion – helping you see life at its very best.
