This patient-education article is written by the cornea service at Suraj Eye Institute, Nagpur.

What is Corneal Topography and Tomography?

The cornea is the eye’s main refracting surface, providing about two-thirds of its focusing power. Tiny variations in corneal curvature and thickness produce visually significant astigmatism and reveal the earliest changes of disease. Two related imaging techniques map these variations:

  • Corneal topography measures the curvature of the anterior (front) corneal surface, traditionally using Placido-disc reflection.
  • Corneal tomography (we use the Anterion, made by Heidelberg Engineering) uses a swept-source OCT scan to image the cornea in cross-section, producing maps of both the anterior and posterior surfaces and the corneal thickness at every point.

Modern tomography is more powerful than topography alone because the earliest signs of keratoconus and post-LASIK ectasia appear on the posterior corneal surface, which only tomography can image.

Anterion Four-Map Refractive Display Anterion Four-Map Display — the Keratoconus Pattern Note how the abnormality on every map sits BELOW the centre (inferior) — the hallmark of keratoconus

a. Axial curvature (front) Inferior steepening → keratoconus suspicion

b. Anterior elevation Focal island of elevation at the cone apex

c. Posterior elevation ⚑ Earliest, most sensitive sign of early ectasia

thinnest d. Pachymetry (thickness) Inferotemporal thinning below the visual axis

flat / thin steep / thick

Figure 1. The Anterion four-map refractive display in early-to-moderate keratoconus. In every map the abnormality sits below the visual axis — the hallmark of keratoconus. (a) Axial curvature shows inferior steepening (the warm zone is pulled downward). (b) Anterior elevation shows a focal island of elevation at the cone apex. (c) Posterior elevation shows a corresponding island — the earliest and most sensitive single sign, often present before anything is visible at the slit lamp. (d) Pachymetry shows corneal thinning displaced inferotemporally, with the thinnest point marked. The warm-to-cool colour scale runs from steep/thick (red) to flat/thin (blue).

What Topography and Tomography Are Used For

  • Keratoconus diagnosis and family screening — detecting subclinical disease in relatives of keratoconus patients from age 10 onwards
  • Refractive surgery screening — mandatory before LASIK, SMILE or PRK. Forme fruste keratoconus must be excluded to prevent post-LASIK ectasia
  • Progression monitoring — serial scans to detect the small changes that justify corneal cross-linking
  • Cataract surgery planning — keratometry, total corneal power and astigmatism for intraocular lens calculations, particularly for toric and premium IOLs
  • Contact lens fitting for irregular corneas (keratoconus, post-graft, post-refractive)
  • Post-keratoplasty follow-up — monitoring graft topography and astigmatism

What to Expect During the Scan

The Anterion is non-contact, painless and takes less than two seconds per eye. The patient sits at the instrument, fixates on a target, and a rotating camera captures fifty cross-sections of the cornea. No drops, no dye and no preparation are needed. Eyes should ideally not have been rubbed for at least an hour before the scan, and contact lens wearers are asked to remove their lenses (soft lenses 48 hours, rigid lenses one to two weeks) before the scan.

Anterion screening before any refractive surgery is mandatory. Forme fruste keratoconus is invisible at the slit lamp but produces a characteristic posterior elevation pattern. Refractive surgery in an eye with subclinical keratoconus leads to ectasia, sometimes years later.
✔ Corneal Imaging at Suraj Eye Institute

Our cornea service offers Anterion swept-source OCT tomography for keratoconus screening, post-refractive ectasia follow-up and cataract surgery planning. We screen family members of keratoconus patients and routinely image every refractive surgery candidate before any laser is offered. Reports are shared and explained to the patient at the time of the scan.

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Frequently Asked Questions

Does the scan involve any radiation or eye drops?
No. Anterion swept-source OCT imaging uses a soft blue light flash and a rotating camera — there is no ionising radiation, no contact and no drops needed. The whole scan takes about two seconds per eye.

Why do I need an Anterion if my vision is correctable with glasses?
Two reasons. First, early keratoconus is invisible at the slit lamp and on a glasses test — only the Anterion detects it. Second, if you are considering refractive surgery (LASIK, SMILE, PRK), Anterion screening is mandatory to ensure your cornea is biomechanically safe to operate on.

Why does my optometrist’s topography differ from the hospital Anterion?
Older Placido-disc topographers map only the front of the cornea. The Anterion swept-source OCT system maps both the front and the back of the cornea and measures the thickness across the entire diameter — three additional pieces of information that are central to modern diagnosis.

How often should I have a repeat scan?
For monitoring known keratoconus, typically every 4–6 months in younger patients and annually once disease is stable. After cross-linking, scans are usually done at 1, 6 and 12 months and then yearly. For post-LASIK follow-up, annual scans are appropriate in most patients.

Is the Anterion available at SEI?
Yes. Anterion swept-source OCT tomography is available at our New Colony campus and is part of every routine cornea consultation, every refractive-surgery work-up and every pre-operative cataract assessment that involves a premium intraocular lens.

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