Keratoconus

The cornea is the clear window at the front of the eye and does much of its focusing. In keratoconus, the cornea becomes thinner and weaker and gradually bulges into a cone. The image becomes distorted and an irregular astigmatism develops, which glasses correct less and less well.

THE CORNEA IN PROFILE

Why the image becomes distorted

A regular cornea focuses light to a point; a cone-shaped cornea scatters it.

1

Normal cornea

Regular curvature: light converges to a point and the image is sharp.

2

Keratoconus

The cornea thins and bulges into a cone: light scatters and the image becomes blurred and distorted.

CLINICAL PHOTOS

Advanced keratoconus: when looking down, the cone-shaped cornea bulges the edge of the lower eyelid (Munson’s sign).

Photo: William Charles Caccamise, Sr, MD · CC BY-SA 4.0 · Wikimedia Commons

Intracorneal ring segments nine days after surgery in an eye with keratoconus: the two clear arcs sit within the thickness of the cornea, around the pupil, and help to regularise its shape.

Photo: Edouard Spooner · CC BY-SA 2.0 · Wikimedia Commons

Topography of a keratoconus (stage II): on the left, the curvature map shows the steepest area (orange and red) below the centre; on the right, the thickness map shows the thinnest cornea at the same spot.

Photo: Elise A. Slim et al. · CC BY 4.0 · Wikimedia Commons

Who is at higher risk?

• It usually starts between adolescence and age 30 and may progress until about 30 to 40.
• Frequent and vigorous eye rubbing is one of the most important risk factors.
• It is more common in people with eye allergies, asthma or atopic dermatitis.
• It can run in families; close relatives should be examined.

What symptoms does it cause?

• Blurred or distorted vision, at distance and near.
• Frequent changes in glasses prescription, especially astigmatism.
• Light sensitivity, glare and halos at night.
• Double or “ghost” images in one eye.

Rarely, in advanced cases, the cornea can suddenly fill with fluid, with rapid loss of vision, pain and a white patch on the cornea. This should be examined urgently.

How is it diagnosed?

In the early stages, keratoconus may not be visible on a routine examination. Corneal topography and tomography map the curvature and thickness at every point, allow early diagnosis and show whether it is progressing by comparing scans over time. That is why these tests are also done before any laser refractive surgery.

How is it treated?

Treatment has two aims: to halt progression and to correct vision.

• Do not rub your eyes: this is the simplest and one of the most important measures. If your eyes itch, the allergy should be treated.
• Corneal cross-linking: using riboflavin (vitamin B2) and ultraviolet light, it strengthens the bonds between corneal fibres. It is indicated when there is progression and aims to halt it, not to correct the prescription.
• Glasses: useful in the early stages.
• Contact lenses: rigid gas-permeable, hybrid or scleral lenses create a regular surface in front of the cornea and are often the best way to see well.
• Intracorneal ring segments: small segments placed within the cornea to make it more regular, in selected cases.
• Phakic intraocular lenses: in some patients with stable keratoconus, to correct short-sightedness and astigmatism.
• Corneal transplant: reserved for advanced cases where vision cannot be corrected any other way. It is needed far less often today.

People with keratoconus should not have LASIK, because it weakens the cornea further. Regular follow-up with corneal tomography is essential, especially in younger patients.

This information does not replace an individual medical assessment. Follow the advice of the team looking after you.