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

What is Anterior Segment OCT?

Anterior segment optical coherence tomography (AS-OCT) is a non-contact, non-invasive imaging test that produces a high-resolution cross-sectional picture of the cornea, anterior chamber and iridocorneal angle. Light beams reflected from each corneal layer build an image rather like an ultrasound, but using light rather than sound and with far higher resolution. Modern Fourier-domain and swept-source instruments image the cornea to micrometre resolution in less than a second per scan, with no contact and no drops required.

Clinical Image
Anterior segment OCT cross-section
(image to be uploaded)
Figure 1. A typical anterior segment OCT cross-section resolves the five layers of the cornea individually — epithelium, Bowman layer, stroma, Descemet membrane and endothelium — together with the anterior chamber, iris and front surface of the crystalline lens. The same scan measures central corneal thickness (pachymetry) and gives anatomical detail of the iridocorneal angle.

What AS-OCT Is Used For

  • Corneal pachymetry — central and peripheral thickness for refractive screening, post-LASIK monitoring and pre-cross-linking assessment
  • Depth assessment of corneal opacities, stromal dystrophies and post-infection scars — determining whether PTK or DALK is appropriate
  • Post-DSAEK / DMEK monitoring — confirming graft attachment, measuring graft thickness, detecting detachment
  • Keratoconus follow-up — epithelial and stromal thickness maps
  • Scleral contact lens fitting — measuring corneal sagittal height for custom lens design
  • Iridocorneal angle assessment — non-contact angle imaging for suspected narrow-angle glaucoma
  • Intraocular lens position after cataract surgery — particularly in pseudophakic bullous keratopathy assessment

What to Expect

The scan is non-contact, painless and takes only seconds per eye. No drops, no dye and no preparation are needed. The patient rests their chin on the support and looks at a fixation target while the instrument captures the cross-section. A clear printed image is available immediately.

AS-OCT complements Anterion, it does not replace it. Anterion (swept-source OCT imaging) gives global maps of the corneal surface and thickness; AS-OCT gives a high-resolution cross-section of individual layers. Both are commonly performed at the same visit when needed.
✔ AS-OCT at Suraj Eye Institute

Anterior segment OCT is available at our cornea clinic and is used routinely for pre-operative planning of lamellar keratoplasty, depth assessment of stromal dystrophies, post-DSAEK / DMEK graft thickness monitoring, scleral contact lens fitting, and assessment of the iridocorneal angle in narrow-angle glaucoma.

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Frequently Asked Questions

Is AS-OCT the same as the Anterion scan?
No. The two are complementary. Anterion swept-source OCT imaging produces a global map of corneal shape and thickness across the entire diameter. AS-OCT produces a high-resolution cross-section of the corneal layers at a chosen location and is particularly useful for measuring the depth of a corneal opacity or assessing a graft.

Does AS-OCT need eye drops?
No — AS-OCT does not require pupil-dilating drops or any other preparation. The scan is non-contact and the test is over in seconds.

Can AS-OCT detect Fuchs dystrophy?
AS-OCT can show the corneal swelling that develops in advanced Fuchs disease, but the diagnostic test for the endothelium itself is specular microscopy. The two are usually done together when staging Fuchs.

Why is the scan helpful before a corneal transplant?
AS-OCT measures exactly how deep the corneal scar or dystrophy goes. If the back layer of the cornea is healthy, a lamellar transplant (DALK) replaces only the diseased front layers and has lower long-term rejection risk than a full-thickness graft (PK).

Is AS-OCT used for glaucoma too?
Yes. The same instrument can image the iridocorneal angle without a contact lens, which is useful when assessing suspected narrow-angle glaucoma or planning laser iridotomy.

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