Accurate biometry is the foundation of a good cataract surgery outcome. It is what lets us choose the exact intraocular lens (IOL) power that will give you the vision you want after surgery. At Suraj Eye Institute we perform biometry on the Heidelberg Anterion — a swept-source OCT-based multi-function platform — for every cataract case.

What is Biometry?

Biometry is the precise optical measurement of the dimensions of the eye. The main measurements used for IOL power calculation are:

• Axial length (AL) — the length of the eye from cornea to retina
• Keratometry (K) — the curvature of the cornea
• Anterior chamber depth (ACD) — from cornea to front of the lens
• Lens thickness (LT) — the thickness of the crystalline lens
• White-to-white (WTW) — the horizontal corneal diameter
• Central corneal thickness — relevant when post-refractive or IOP interpretation is important

These numbers feed into IOL calculation formulae — Barrett Universal II, Hill-RBF, Haigis, SRK/T and others — which output the recommended IOL power.

Why Anterion?

Swept-source OCT technology

Anterion uses a 1300 nm swept-source OCT laser. Compared to older partial-coherence interferometry or low-coherence optical biometers, this wavelength:

• Penetrates dense cataracts better — successful axial length measurement in more eyes, including many white cataracts
• Resolves individual ocular structures sharply, reducing measurement noise
• Provides simultaneous full anterior segment OCT imaging

All-in-one workflow

A single Anterion scan provides:

• Biometry (axial length, ACD, LT, CCT)
• Keratometry — both anterior and posterior corneal surface
• Corneal topography and tomography
• Anterior segment OCT
• IOL power calculation with multiple modern formulae

This integrated workflow reduces errors from transferring data between devices and gives the surgeon a comprehensive snapshot of the anterior segment in one sitting.

Toric IOL planning

Anterion measures posterior corneal astigmatism directly, which matters for accurate toric IOL alignment. It also provides images that can be used for intra-operative iris registration of toric IOLs.

Post-refractive surgery cases

For patients who have previously had LASIK, PRK or SMILE, accurate keratometry is especially difficult. Anterion’s total keratometry and ray-tracing-based formulae (Barrett True-K, Haigis-L) help us give reliable post-refractive surgery IOL calculations.

How the Scan is Done

Biometry at SEI is done at your pre-operative assessment visit. You sit in front of the Anterion, rest your chin and forehead on the supports, and fixate a small target light. The scan is non-contact and takes only a few seconds per eye. No drops, no touching of the eye.

What Happens with the Data

After the scan:

• Anterion outputs biometric values and IOL power tables for all IOL models in our formulary
• The surgeon reviews the measurements for consistency — both eyes are compared, and any discrepancy is re-checked
• Formula selection is based on axial length and other parameters — short and long eyes use specific formulae for best accuracy
• Your chosen IOL type (see choosing the right IOL) and your target refraction (our aim: 6/6 for distance and N/6 for near without glasses, where possible) determine the final IOL power selected
• A back-up IOL power is noted in case of intra-operative findings

When Biometry is Difficult

Some eyes are inherently harder to measure:

• Very dense or white cataracts — Anterion still works in most cases; supplementary ultrasound B-scan is used when optical biometry fails
• Macular pathology affecting fixation — special fixation aids and averaging help
• Silicone oil filled eyes — specific refractive indices are used
• Post-refractive surgery eyes — Barrett True-K, Haigis-L and ray-tracing formulae are selected
• Keratoconus — total keratometry from Anterion is used along with keratoconus-specific formulae
• Very short or very long eyes — eye-length-specific formulae (Barrett, Hoffer QST) are used

Frequently Asked Questions