ICL Sizing Explained: How the Correct Lens Size and Vault Are Chosen

Author: Dr Val Phua
Estimated reading time: 16 minutes

Implantable Collamer Lens surgery—commonly known as ICL surgery—requires more than selecting the correct lens power.

The surgeon must also choose the correct physical size of the ICL.

These are two separate decisions:

ICL power determines how much myopia and astigmatism the lens corrects.
ICL size determines how the lens fits inside the eye.

An ICL with the correct optical power but an unsuitable physical size may still produce problems.

A lens that is too small may sit too close to the natural crystalline lens. A lens that is too large may sit too far forwards and crowd the iris or drainage angles.

The aim of ICL sizing is to achieve an appropriate vault—the space between the back of the ICL and the front of the natural lens.

Accurate sizing helps reduce the risks of:

Cataract
Raised eye pressure
Narrowing of the drainage angles
Pigment dispersion
Corneal endothelial cell loss
Toric ICL rotation
Lens exchange or removal

Modern imaging, refined sizing formulas and artificial-intelligence models have improved ICL planning. However, no measurement or formula can predict postoperative vault perfectly because the ICL rests within internal structures that vary in size, shape and behaviour between individuals.

What Does ICL Size Mean?

ICL size refers to the lens’s overall diameter from one end to the other, including its supporting footplates.

The lens does not attach to the cornea or natural lens. Its footplates rest within the ciliary sulcus behind the iris.

Under current United States FDA labelling, available EVO ICL overall diameters include:

12.1 mm
12.6 mm
13.2 mm
13.7 mm

Availability may differ according to the lens model and country.

A difference of 0.5 or 0.6 mm may appear small, but it can significantly affect how the lens curves and sits inside the eye.

If the ICL Is Relatively Small

The lens may sit flatter, producing a lower vault.

If the ICL Is Relatively Large

The lens may be compressed more strongly within the eye, causing it to bow forwards and produce a higher vault.

However, the relationship is not completely predictable. Internal anatomy, lens power, ciliary sulcus shape and the orientation of implantation also influence vault.

Is ICL Size the Same as ICL Power?

No.

A patient may hear two different sets of numbers during ICL planning.

ICL Optical Power

The optical power is measured in dioptres and corrects:

Myopia
Astigmatism
The spherical equivalent of the prescription

For example, one lens may have a spherical power of −10.00 D.

ICL Physical Size

The physical size is measured in millimetres.

For example, the surgeon may select a 12.6 mm or 13.2 mm ICL.

Two patients with the same spectacle prescription may require different physical ICL sizes because their internal eye dimensions are different.

Similarly, two patients with similar-sized eyes may require different lens powers because their prescriptions are different.

Where Does the ICL Sit?

The ICL is positioned:

Behind the iris
In front of the natural crystalline lens
Within the posterior chamber
With its supporting footplates resting in the ciliary sulcus

The ciliary sulcus is an internal groove-like region behind the iris.

Unlike the white-to-white corneal diameter, the ciliary sulcus cannot be seen directly during a routine external examination. It must be estimated or imaged using specialised measurements.

The shape of the sulcus also varies between individuals. It may be horizontally oval, vertically oval or asymmetrical rather than perfectly circular. This is one reason why a simple external measurement cannot predict the fit of every ICL perfectly.

What Is ICL Vault?

Vault is the central distance between:

The back surface of the ICL
The front surface of the natural crystalline lens

Vault is usually measured in micrometres, or microns.

One millimetre equals 1,000 microns.

FDA professional guidance describes an intended postoperative vault of approximately one central corneal thickness. It considers approximately 250 to 900 microns—about 50% to 150% of central corneal thickness—a broadly desirable range. However, a vault outside this range does not automatically require lens exchange or removal when the eye remains otherwise healthy.

The ideal vault is not a single exact number that applies to every eye.

The surgeon also considers:

The patient’s age
Natural-lens thickness
Eye pressure
Drainage-angle width
Endothelial cell count
ICL position
Pupil shape
Evidence of iris contact
Whether the vault is stable or changing
Whether cataract or other complications are developing

Why Is Vault Important?

The ICL must remain sufficiently separated from the natural lens without excessively crowding the front of the eye.

If Vault Is Too Low

A very low vault may increase concern about:

Proximity or contact with the natural lens
Reduced aqueous-fluid circulation
Anterior subcapsular cataract
Progressive reduction in vault as the natural lens thickens with age

If Vault Is Too High

A very high vault may:

Push the iris forwards
Narrow the drainage angles
Raise eye pressure
Cause iris contact
Release iris pigment
Contribute to pupil distortion
Bring the ICL closer to the corneal endothelium

Correct sizing aims to balance these competing concerns.

Does Low Vault Always Cause Cataract?

No.

Some patients with relatively low vault remain stable for many years without developing cataract.

The significance depends on:

The actual distance between the ICL and natural lens
Whether physical contact is present
The patient’s age
Natural-lens clarity
Changes in vault over time
The central-port design
Aqueous-fluid circulation

A five-year study comparing eyes with low vault and eyes with conventionally normal vault reported comparable safety, refractive efficacy and visual outcomes in its selected population. This suggests that low vault should be interpreted together with clinical findings rather than treated as an automatic indication for exchange.

However, a very low vault accompanied by anterior subcapsular lens opacity or direct contact remains clinically important.

Does High Vault Always Require Lens Exchange?

No.

Some eyes with high vault maintain:

Normal eye pressure
Adequately open drainage angles
Stable endothelial cell counts
A clear natural lens
Good vision
No significant symptoms

Observation may be appropriate when the anatomy remains safe.

Exchange becomes more likely when high vault is associated with:

Progressive angle narrowing
Raised eye pressure
Pigment dispersion
Pupil distortion
Endothelial concerns
Significant glare or discomfort

FDA guidance specifically notes that a vault outside the intended range may not necessarily require exchange or removal in the absence of symptoms or associated complications.

How Was ICL Size Traditionally Chosen?

Traditional ICL sizing has primarily used:

Horizontal white-to-white corneal diameter
Anterior chamber depth

The manufacturer’s sizing nomogram then recommends one of the available ICL diameters.

During the original United States clinical study, the calculated lens length was based on adding approximately 1.1 to 1.6 mm to the horizontal white-to-white measurement, with the amount influenced by anterior chamber depth. The current professional instructions contain a table matching white-to-white and true anterior chamber depth to a recommended lens diameter.

This method is simple, widely available and clinically established.

However, it has an important limitation: the ICL rests in the ciliary sulcus, while white-to-white measures the visible cornea.

What Is White-to-White?

White-to-white, commonly abbreviated as WTW, is the horizontal distance between the visible borders of the cornea.

It is measured from one corneal limbus to the other.

The limbus is the transition between:

The clear cornea
The white sclera

WTW can be measured using:

Corneal topography devices
Optical biometers
Anterior-segment OCT
Digital photography
Manual callipers

It is non-contact and easy to obtain.

Why Is White-to-White Used?

White-to-white is used because it provides a convenient external estimate of the eye’s overall anterior dimensions.

Advantages include:

Rapid measurement
No contact with the eye
Good repeatability on many modern devices
Wide availability
Integration with established manufacturer nomograms

However, WTW is only a surrogate for the internal ciliary sulcus diameter.

A large cornea does not always correspond to a proportionately large sulcus, and a smaller cornea does not always indicate a small internal sulcus.

What Are the Limitations of White-to-White?

It Measures the Cornea, Not the Ciliary Sulcus

The ICL footplates sit within the sulcus behind the iris.

WTW measures a visible external structure that is anatomically separate from the lens’s final resting position.

Devices Can Produce Different Results

Different instruments may define the corneal border differently.

A patient may therefore receive slightly different WTW values from:

An optical biometer
A topographer
An anterior-segment camera
Manual measurement

Interdevice measurement bias can influence the recommended ICL size when the eye lies close to the boundary between two lens sizes.

WTW and Sulcus Size Do Not Always Match

Research has shown that the difference between WTW and sulcus-to-sulcus diameter can be greater in eyes with unusual WTW measurements or anterior chamber depths. These patients may have a higher risk of an unexpected vault when sizing relies mainly on WTW.

It Does Not Describe Sulcus Shape

The ciliary sulcus may be:

Oval
Vertically elongated
Horizontally elongated
Asymmetrical
Different between the two eyes

One horizontal external measurement cannot fully represent this three-dimensional anatomy.

What Is Anterior Chamber Depth?

Anterior chamber depth, or ACD, describes the space between the cornea and the natural lens.

For ICL suitability and FDA labelling, the relevant measurement is the true ACD:

From the back surface of the cornea
To the front surface of the crystalline lens

Some devices instead measure from the front surface of the cornea. In that situation, corneal thickness must be subtracted to obtain the true ACD.

Under current United States labelling, EVO ICL requires a true anterior chamber depth of at least 3.0 mm. Local indications may differ.

Why Does Anterior Chamber Depth Affect Sizing?

Anterior chamber depth provides information about how much internal space is available.

A deeper eye may accommodate a larger or more anteriorly vaulted lens differently from a shallower eye.

A shallow anterior chamber can increase concern about:

Narrow drainage angles
Endothelial cell proximity
Iris crowding
Excessive postoperative vault

ACD is therefore important for both:

Determining whether ICL surgery is suitable
Selecting the lens size

However, two eyes with the same ACD may still have different sulcus widths and postoperative vaults.

What Is Sulcus-to-Sulcus Measurement?

Sulcus-to-sulcus, or STS, is the internal distance between opposite sides of the ciliary sulcus.

Because the ICL footplates rest in the sulcus, STS appears intuitively more directly related to lens fit than WTW.

STS can be measured in:

The horizontal meridian
The vertical meridian
Oblique meridians

Research has shown that including STS in sizing formulas can improve vault predictability compared with relying on traditional WTW-based sizing alone.

How Is Sulcus-to-Sulcus Measured?

STS is most commonly assessed using ultrasound biomicroscopy, or UBM.

UBM uses very-high-frequency ultrasound to image structures behind the iris, including:

The ciliary sulcus
Ciliary body
Zonules
Posterior iris surface
Natural lens
Internal chamber dimensions

Advantages of UBM

Direct visualisation behind the iris
Measurement of horizontal and vertical STS
Assessment of ciliary sulcus shape
Identification of ciliary body abnormalities
Evaluation of lens position and orientation

Limitations of UBM

Requires contact or an immersion interface
More operator-dependent than non-contact optical imaging
Patient positioning can influence measurements
Image quality and landmark identification may vary
Different UBM devices or operators may produce different values
It requires additional time and expertise

STS is useful, but it is not a perfect solution on its own.

Is STS Always Better Than WTW?

Not necessarily in every clinical setting.

Some studies have shown better vault prediction when STS is included. Others have found that modern optical measurements and multivariable formulas can perform similarly or better without direct STS measurement.

The practical value of STS depends on:

UBM image quality
Operator experience
Repeatability
Whether horizontal and vertical measurements are obtained
The formula into which the measurement is entered
The patient’s anatomy

The best planning approach generally combines several measurements rather than treating one dimension as infallible.

Why Are Horizontal and Vertical STS Different?

The ciliary sulcus is often not perfectly circular.

In many eyes:

Vertical STS is greater than horizontal STS
The sulcus is elliptical
The degree of asymmetry differs between patients

This has implications for:

Lens size
Lens orientation
Toric stability
Postoperative vault

A lens implanted horizontally may behave differently from one placed vertically or obliquely within the same eye.

Recent research continues to explore how horizontal-to-vertical sulcus differences can guide individualised sizing and orientation.

What Is Angle-to-Angle or Anterior Chamber Width?

Angle-to-angle, also called anterior chamber width, is the internal distance between opposite drainage-angle landmarks.

It is commonly measured with anterior-segment OCT.

Unlike WTW, angle-to-angle is an internal measurement.

Although the ICL footplates do not rest directly at the drainage angles, anterior chamber width provides information about the size of the front of the eye and can contribute to vault prediction.

What Is Crystalline Lens Rise?

Crystalline lens rise, sometimes abbreviated as CLR, describes how far the natural lens rises above a reference line across the anterior chamber.

A more anteriorly positioned or more prominent natural lens may reduce the available space between the ICL and crystalline lens.

CLR can therefore influence postoperative vault.

Anterior-segment OCT-based sizing research has found anterior chamber width and crystalline lens rise to be significant predictors of postoperative vault.

What Is Lens Thickness?

The natural crystalline lens gradually thickens with age.

A thicker lens may:

Occupy more internal space
Sit closer to the ICL
Contribute to lower vault
Reduce anterior chamber depth

Lens thickness is therefore relevant both before surgery and during long-term follow-up.

Studies have identified crystalline lens thickness, ICL size and horizontal and vertical STS as factors that influence postoperative vault.

What Other Measurements May Affect ICL Sizing?

Modern formulas may incorporate:

White-to-white diameter
True anterior chamber depth
Angle-to-angle distance
Sulcus-to-sulcus diameter
Crystalline lens rise
Natural-lens thickness
Ciliary body inner diameter
Zonule-to-zonule distance
Anterior chamber angle
Pupil diameter
ICL optical power
Patient age
Sex
Preoperative refraction

A study developing new sizing parameters found that vault prediction was influenced by several internal structures, including STS, ciliary body dimensions, zonular measurements and lens rise.

Why Does ICL Optical Power Affect Vault?

Higher-powered myopic ICLs do not have exactly the same shape or thickness profile as lower-powered lenses.

The physical design of the optic can affect how the lens bends and vaults inside the eye.

This means postoperative vault depends not only on overall diameter but also on:

ICL power
Lens model
Toric design
Internal eye anatomy

A sizing formula that ignores lens power may be less accurate for certain prescriptions.

Does Age Affect Vault?

Yes.

Age may influence vault through changes in:

Natural-lens thickness
Anterior chamber depth
Ciliary body anatomy
Pupil behaviour
Tissue flexibility

Vault commonly decreases gradually as the natural lens thickens with age.

An older patient may therefore require different interpretation from a younger patient with the same immediate postoperative vault.

Age should also be considered when deciding whether a borderline low vault is likely to remain safe over the expected duration of implantation.

Does Pupil Size Affect Vault?

Vault can change slightly as the pupil constricts and dilates.

Pupil movement alters:

Iris configuration
Ciliary muscle activity
Contact between the iris and ICL
Position of the ICL

Vault measured under bright-light conditions may therefore differ from vault measured in dim lighting.

This is one reason that a single measurement should not be viewed as an absolute, unchanging property.

Can Implantation Orientation Change Vault?

Yes.

Because the ciliary sulcus is frequently elliptical, changing the ICL’s orientation may alter the amount of compression applied to the lens.

For example, implanting a non-toric ICL vertically rather than horizontally may reduce vault in an eye whose vertical sulcus diameter is larger than its horizontal diameter.

A customised approach using STS dimensions, ciliary sulcus morphology and intended lens orientation has been reported to improve the proportion of eyes achieving a desirable vault.

What About Toric ICLs?

A toric ICL must be aligned with the intended astigmatic axis.

The surgeon cannot freely choose any orientation solely to optimise vault because rotating the lens changes the astigmatism correction.

The lens design allows limited planned rotation for axis alignment, but excessive rotation from the intended orientation is not desirable. FDA instructions state that the EVO toric ICL is designed to require no more than 22.5 degrees of rotation from its manufactured orientation.

Sizing and toric alignment must therefore be considered together.

What Imaging Devices Are Used for ICL Planning?

Optical Biometry

Optical biometers may measure:

White-to-white
Anterior chamber depth
Corneal thickness
Lens thickness
Axial length

Advantages include speed, repeatability and non-contact measurement.

Corneal Topography or Tomography

These devices assess:

Corneal shape
Corneal diameter
Astigmatism
Corneal thickness
Keratoconus risk

They may also provide WTW and pupil measurements.

Anterior-Segment OCT

Anterior-segment OCT provides non-contact cross-sectional imaging of:

Anterior chamber depth
Angle-to-angle distance
Crystalline lens rise
Drainage-angle anatomy
Postoperative vault

Advantages include:

High resolution
Rapid imaging
Good patient comfort
Repeatable postoperative vault measurement

Limitations include reduced visibility of some structures located behind the pigmented iris.

Ultrasound Biomicroscopy

UBM can image structures behind the iris, including the ciliary sulcus.

It may be particularly helpful when:

WTW and internal dimensions do not appear to match
The eye is between two lens sizes
Previous surgery produced an unexpected vault
Sulcus shape or ciliary body anatomy needs assessment
Customised orientation is being considered

How Does the Surgeon Choose Between Two Sizes?

Some patients fall clearly within the range for one ICL size.

Others lie near the boundary between two sizes.

For example, measurements may support either:

A 12.6 mm lens
A 13.2 mm lens

The surgeon then considers the likely consequences of each choice.

Choosing the Smaller Size May:

Reduce the risk of excessive vault
Preserve wider drainage angles
Increase the risk of lower vault
Potentially affect toric stability in some anatomies

Choosing the Larger Size May:

Increase separation from the natural lens
Improve stability in some eyes
Increase the risk of high vault
Narrow the drainage angles

The final decision may incorporate:

WTW
ACD
STS
Anterior chamber width
Lens rise
Lens thickness
Age
ICL power
Sulcus shape
Surgeon experience
Expected implantation orientation

There is no universal rule that the larger or smaller option is always safer.

What Is a Sizing Nomogram?

A nomogram is a structured calculation or table used to recommend an ICL size based on preoperative measurements.

Examples include:

Manufacturer WTW–ACD nomograms
UBM-based formulas
Anterior-segment OCT formulas
Multivariable regression models
Machine-learning models
Surgeon-specific nomograms

A comparative study of multiple available nomograms found that predictive performance varied and that no formula eliminated unexpected postoperative vault completely.

Why Do Different Formulas Recommend Different Sizes?

Different formulas may use different combinations of:

External measurements
Internal measurements
Lens power
Patient demographics
Imaging platforms
Historical surgical outcomes

They may also have been developed using different:

Ethnic populations
Age groups
ICL models
Surgical techniques
Measurement devices

A formula trained in one population may not perform identically in another.

This is why external validation is important before a new formula is adopted widely.

Can Artificial Intelligence Improve ICL Sizing?

Artificial-intelligence and machine-learning models are increasingly being studied for ICL sizing and vault prediction.

These systems may analyse:

Multiple numerical measurements
Anterior-segment OCT data
Ultrasound images
Patient age and prescription
ICL power and size
Interactions between anatomical variables

Studies have reported that machine-learning approaches can outperform traditional linear models or manufacturer nomograms within their study datasets.

Deep-learning systems have also been developed to interpret raw OCT or ultrasound images directly and estimate postoperative vault.

Does AI Guarantee the Correct ICL Size?

No.

AI models have several limitations:

They may be trained mainly on one ethnic or geographic population
They may use measurements from a particular device
They may not perform identically with another ICL model
Retrospective datasets may contain selection bias
A model can reproduce errors in its training data
External validation may be limited
Clinical judgement remains necessary

AI is best viewed as a decision-support tool rather than a replacement for the surgeon.

A 2025 AI model showed promising robustness using a relatively small number of parameters, while a separate externally validated image-based model also reported improved vault prediction. These developments are encouraging, but they still require continued validation before being treated as universal standards.

Why Can Vault Still Be Unexpected?

Even with careful measurement, postoperative vault may differ from prediction because of:

Measurement error
Differences between devices
Sulcus asymmetry
Ciliary body morphology
Lens orientation
ICL power
Pupil size
Natural-lens position
Tissue flexibility
Postoperative settling
Changes in lighting conditions
Individual biological variation

The ICL is a flexible lens resting within dynamic living tissue, not a rigid implant fixed to a precisely measurable frame.

Can the Two Eyes Have Different ICL Sizes?

Yes.

The two eyes may differ in:

White-to-white diameter
Sulcus-to-sulcus diameter
Anterior chamber depth
Lens rise
Ciliary sulcus shape
Astigmatic axis
Lens power

Many patients receive the same ICL size in both eyes, but this should not be assumed automatically.

Each eye should be measured and planned individually.

Can the First Eye Help Determine the Size for the Second Eye?

Potentially.

The two eyes of one person often have similar anatomy.

In staged surgery, the early postoperative vault in the first eye may provide useful information when selecting the ICL size for the second eye.

A 2025 study found that first-eye vault could assist second-eye size selection and prediction. However, this strategy is only relevant when surgery is performed sequentially and the eyes are sufficiently similar.

It does not replace independent measurements of both eyes.

When Is Vault Checked After Surgery?

FDA professional guidance recommends assessing vault approximately 24 hours after implantation.

Vault may also be checked at:

One week
One month
Three to six months
Yearly follow-up
Any visit when symptoms or pressure changes occur

The exact schedule depends on:

Initial vault
Eye pressure
Drainage-angle appearance
Natural-lens clarity
Endothelial cell density
Patient age
Other risk factors

Does Vault Change During the First Day?

Yes.

Vault can change during the first hours and days as:

The pupil changes size
Surgical medication wears off
Viscoelastic is removed
Inflammation settles
The ICL adjusts within the sulcus

Research has shown that vault may decrease and subsequently rise during the early postoperative period rather than remaining fixed immediately after implantation.

A very early measurement should therefore be interpreted together with subsequent follow-up.

Does Vault Decrease Over the Years?

Vault commonly decreases gradually over time.

Possible reasons include:

Natural-lens thickening
Changes in anterior chamber depth
Age-related anatomical changes
Ciliary body changes

A gradual reduction does not necessarily indicate incorrect initial sizing.

The clinical importance depends on whether it is associated with:

Lens opacity
Natural-lens contact
Symptoms
Other anatomical changes

Long-term monitoring is particularly important in younger patients because the ICL may remain inside the eye for several decades.

How Is Vault Measured After Surgery?

Slit-Lamp Estimation

The surgeon can estimate vault by comparing it with central corneal thickness.

This provides a rapid clinical assessment.

Anterior-Segment OCT

OCT provides a numerical vault measurement in microns and can also assess:

Drainage angles
Iris configuration
ICL position
Natural-lens relationship

Ultrasound Biomicroscopy

UBM may be used when more detailed assessment of:

Footplate position
Ciliary sulcus
ICL orientation
Iris contact

is required.

What Happens if the ICL Is Too Small?

A relatively undersized ICL may produce:

Low vault
Increased proximity to the natural lens
Anterior subcapsular cataract concern
Reduced lens stability
Toric rotation in some cases

Management depends on the findings.

Observation May Be Appropriate When:

The natural lens is clear
There is no ICL–lens contact
Vision is good
Vault is stable
Eye pressure is normal

Exchange May Be Considered When:

Vault is extremely low
The ICL contacts the natural lens
An anterior subcapsular opacity develops
A toric lens repeatedly rotates
The anticipated long-term risk is unacceptable

What Happens if the ICL Is Too Large?

An oversized ICL may produce:

Excessive vault
Drainage-angle narrowing
Raised eye pressure
Iris contact
Pigment dispersion
Pupil distortion
Endothelial concerns

Management may include:

Observation
More frequent pressure and angle monitoring
Reorientation of a non-toric ICL
Exchange for a smaller lens
Removal

A 2026 size-exchange study found that downsizing reliably reduced excessive vault, while exchanging for the same size produced little vault change. This supports selecting a genuinely smaller lens when excessive size is the underlying problem.

Can an ICL Be Rotated to Change Vault?

A non-toric ICL may sometimes be rotated from a horizontal to a more vertical orientation.

If the vertical sulcus is larger than the horizontal sulcus, this can reduce compression and lower the vault.

This strategy is anatomy-dependent and is not suitable in every case.

A toric ICL cannot usually be rotated freely because its optical axis must remain aligned with the patient’s astigmatism.

How Common Is Exchange for Sizing Problems?

ICL exchange is uncommon but recognised.

A seven-year series found that approximately 2% of implanted central-port ICLs required exchange or removal, with inappropriate vault being the most common reason.

More recent high-volume data have reported lower exchange rates, although rates vary according to:

Lens model
Patient selection
Follow-up duration
Sizing method
Definition of exchange
Surgical centre

Inappropriate sizing and off-label use remain important contributors to reported adverse events, reinforcing the need for careful planning and postoperative vault assessment.

Is Lens Exchange Dangerous?

ICL exchange is generally feasible, but it is another operation inside the eye.

Potential risks include:

Corneal endothelial cell loss
Iris injury
Natural-lens injury
Cataract
Raised eye pressure
Inflammation
Infection
Residual refractive error

The aim of accurate primary sizing is to minimise the need for secondary surgery.

However, when an unsuitable vault poses a greater long-term risk, exchange may be safer than leaving the original lens in place.

Can Perfect Sizing Eliminate All ICL Risks?

No.

Accurate sizing reduces several important risks but cannot prevent complications unrelated to size.

These include:

Infection
Steroid response
Retinal disease associated with high myopia
Natural cataract formation
Myopia progression
Inflammation
Surgical trauma

Sizing is one essential component of safe ICL surgery, not the only one.

What Tests Should Patients Expect Before ICL Surgery?

A comprehensive assessment may include:

Refraction

To determine the optical ICL power.

Corneal Topography and Tomography

To assess corneal shape and exclude progressive corneal disease.

White-to-White Measurement

To estimate the overall horizontal anterior eye dimension.

True Anterior Chamber Depth

To confirm sufficient space for implantation.

Anterior Chamber Width or Angle-to-Angle Distance

To assess internal anterior-segment size.

Crystalline Lens Rise and Thickness

To estimate how much the natural lens projects forwards.

Sulcus-to-Sulcus Measurement

UBM may be used to image the intended resting location of the ICL.

Drainage-Angle Assessment

Gonioscopy or imaging confirms that the angles are sufficiently open.

Endothelial Cell Count

To confirm adequate corneal endothelial reserve.

Pupil Size

To help assess possible glare and halo risk.

Dilated Retinal Examination

Particularly important in moderate and high myopia.

What Questions Should You Ask About ICL Sizing?

Useful questions include:

What ICL size do you recommend?
Which measurements were used?
What are my white-to-white and anterior chamber depth?
Did you measure my anterior chamber width?
Was sulcus-to-sulcus imaging necessary?
Is my eye close to the boundary between two sizes?
What postoperative vault do you expect?
How will vault be measured after surgery?
Are my drainage angles sufficiently open?
How does my age affect the expected long-term vault?
Would a toric lens limit the possible implantation orientation?
What would happen if my vault were higher or lower than expected?
How often will the vault be monitored?

Frequently Asked Questions About ICL Sizing

How Does the Surgeon Know Which ICL Size to Use?

The surgeon combines measurements of the cornea and internal eye, usually including WTW and ACD, with an established sizing nomogram.

Additional imaging such as anterior-segment OCT or UBM may refine the decision.

Are There Different ICL Sizes?

Yes.

Under United States FDA labelling, the available overall diameters are 12.1, 12.6, 13.2 and 13.7 mm. Available models may differ between markets.

Is the Biggest ICL Better?

No.

A lens that is too large may cause excessive vault, angle narrowing and raised eye pressure.

Is a Smaller ICL Safer?

Not automatically.

A lens that is too small may sit too close to the natural lens and may be less rotationally stable.

What Is a Good ICL Vault?

A broadly desirable range is often described as approximately 250 to 900 microns, but the ideal vault is individual.

A measurement outside that range does not automatically mean that the lens is unsafe.

Is 500 Microns the Perfect Vault?

Approximately 500 microns is often used as a convenient reference because it is close to average central corneal thickness.

It is not a universal perfect number.

Is Low Vault Dangerous?

It may increase cataract concern, particularly when the ICL is extremely close to or touching the natural lens.

Some relatively low-vault eyes remain safe for years with careful monitoring.

Is High Vault Dangerous?

It may narrow the drainage angles and increase pressure, pigment or endothelial concerns.

Some high-vault eyes remain stable without requiring exchange.

Can Vault Change After Surgery?

Yes.

It can vary with pupil size during the day and may gradually decrease as the natural lens thickens with age.

Can WTW Alone Choose the Correct Size?

WTW and ACD form the basis of traditional sizing, but they do not fully describe the ciliary sulcus.

Additional internal measurements may be helpful, especially in borderline or unusual eyes.

Is UBM Required for Every Patient?

Not necessarily.

Some surgeons achieve reliable results using modern optical imaging and validated nomograms.

UBM may be particularly valuable when the anatomy is unusual, measurements disagree or previous sizing was unexpected.

Is Sulcus-to-Sulcus More Accurate?

It measures anatomy closer to the ICL’s resting location and may improve vault prediction when measured reliably.

However, it remains operator-dependent and does not eliminate prediction error.

Can AI Choose My ICL Size?

AI may support the surgeon by combining multiple measurements and predicting vault.

It should not replace clinical judgement or postoperative monitoring.

Can the Two Eyes Need Different Sizes?

Yes.

Each eye should be measured and planned independently.

Can the Lens Be Exchanged if the Size Is Wrong?

Yes.

An oversized lens may be exchanged for a smaller one, while an undersized or rotationally unstable lens may be exchanged for a larger one when appropriate.

Does Lens Exchange Restore a Normal Vault?

It often moves the vault in the intended direction, but the exact change cannot be guaranteed.

Does Toric ICL Sizing Differ?

The same anatomical principles apply, but toric lenses must also remain aligned with the intended astigmatic axis.

The surgeon must balance vault, physical stability and rotational alignment.

Is ICL Sizing More Important for High Myopia?

Sizing is important at every prescription.

Very-high-powered lenses may have different optical geometry, and highly myopic patients may also have unusual anterior-segment dimensions.

Does Correct Sizing Guarantee No Cataract?

No.

It reduces vault-related cataract risk but cannot prevent natural age-related cataract or accidental surgical contact with the natural lens.

Do I Need Long-Term Vault Checks?

Yes.

Vault can change over time, and some vault-related complications initially cause few symptoms.

Key Takeaway

ICL sizing determines how the implant fits inside the eye.

It is separate from ICL power:

Power corrects myopia and astigmatism.
Size influences lens position, stability and vault.

Traditional sizing uses:

Horizontal white-to-white diameter
True anterior chamber depth

Modern planning may also incorporate:

Sulcus-to-sulcus diameter
Anterior chamber width
Crystalline lens rise
Natural-lens thickness
Ciliary body anatomy
ICL power
Pupil size
Patient age
Implantation orientation

The aim is to achieve an appropriate vault between the ICL and natural lens.

A lens that is too small may produce low vault and cataract concern. A lens that is too large may produce high vault, angle narrowing and raised eye pressure.

No sizing formula is perfect because the ICL rests within complex, dynamic and partly hidden anatomy. Anterior-segment OCT, UBM, multivariable formulas and artificial intelligence can improve prediction, but they cannot eliminate individual variation.

The safest approach combines:

Careful patient selection
Accurate and repeatable measurements
Use of a validated sizing method
Experienced clinical judgement
Postoperative vault and pressure checks
Long-term monitoring

An unexpected vault does not automatically mean that the operation has failed or that the ICL must be exchanged. The decision depends on the complete clinical picture, including eye pressure, drainage angles, endothelial cells, natural-lens clarity, symptoms and changes over time.

References

US Food and Drug Administration. EVO and EVO+ Visian Implantable Collamer Lens: Instructions for Use. 2022.
Thompson V, et al. Implantable Collamer Lens Procedure Planning: A Review of Sizing and Vault. 2024. PMID: 38601168.
Moshirfar M, et al. Comparative Evaluation of Multiple Nomograms for Predicting Postoperative Vault After Implantable Collamer Lens Surgery. 2024. PMID: 37702514.
Reinstein DZ, et al. Comparison of Postoperative Vault Height Predictability Using White-to-White and Sulcus Diameter-Based ICL Sizing. 2013. PMID: 23311739.
Kojima T, et al. Optimisation of an Implantable Collamer Lens Sizing Method Using High-Frequency Ultrasound Biomicroscopy. 2012. PMID: 22245462.
Guber I, et al. Correcting Interdevice Bias of Horizontal White-to-White and Sulcus-to-Sulcus Measurements for ICL Size Selection. 2016. PMID: 26454242.
Nakamura T, et al. Implantable Collamer Lens Sizing Method Based on Swept-Source Anterior-Segment OCT. 2018. PMID: 29294311.
Chen X, et al. Effect of the Difference Between White-to-White and Sulcus-to-Sulcus Diameters on Vault After ICL Implantation. 2021. PMID: 34460084.
Zhu QJ, et al. Validation of a Vault Prediction Model Based on Sulcus-to-Sulcus Measurements. 2022.
Reinstein DZ, et al. New Sizing Parameters and Model for Predicting Postoperative Vault for the Implantable Collamer Lens. 2022. PMID: 35536711.
Wei R, et al. Outcomes of EVO ICL Using a Customised Non-Horizontal Implantation Orientation. 2022. PMID: 35415777.
Russo A, et al. Predictability of ICL Vault Using Machine Learning of Preoperative Anterior-Segment OCT Measurements. 2023. PMID: 36913536.
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Zhu J, et al. Enhancing Vault Prediction and ICL Sizing Through Machine Learning. 2024. PMID: 38466764.
Hirabayashi MT, et al. Vault Accuracy Using Deep-Learning Technology and Preoperative Ultrasound Imaging. 2024. PMID: 38651696.
Yamashita K, et al. Enhanced ICL Sizing Accuracy Using Advanced Optical Measurements. 2024. PMID: 39094990.
Wu W, et al. Development and Validation of a Novel Vault Prediction Formula. 2024. PMID: 39152392.
Sheng P, et al. Using Artificial Intelligence to Predict Implantable Collamer Lens Vault. 2025. PMID: 40985791.
Li H, et al. Using First-Eye Early Vault to Determine ICL Size for the Second Eye. 2025. PMID: 39325572.
Zéboulon P, et al. Validation of a New Image-Based Implantable Collamer Lens Sizing Algorithm. 2025–2026. PMID: 40827890.
Silva R, et al. Long-Term Efficacy and Safety of Low Versus Normal Vault Following ICL Implantation. 2026. PMID: 40790614.
Choi H, et al. Size Exchange and Vault Response in Posterior-Chamber Phakic Intraocular Lens Implantation. 2026. PMID: 42017508.