What is keratoconus?

Keratoconus affects the cornea, the clear round-shaped front surface of the eye. This becomes progressively thinner and weaker over time, eventually causing a cone-shaped protrusion to develop. The abnormal change of shape causes a person to have blurred and distorted sight as it prevents the light that enters their eye from being correctly focused.

A cartoon of a person's eye in profile sowing the cornea as cone-shaped instead of round.

The cornea becomes cone-shaped in keratoconus

Keratoconus is estimated to affect between one in 500 to 2,000 people worldwide. But it may be more common in certain populations.

Most people who develop keratoconus have no family history of the condition. But keratoconus can occasionaly appear to run in families and also sometimes occur as part of another genetic eye condition, such as Leber congenital amaurosis or retinitis pigmentosa – or a broader inherited syndrome affecting many parts of the body such as Down’s, Marfan or Ehlers-Danlos syndromes.

What causes keratoconus?

Scientists do not understand exactly what causes keratoconus. But it is thought that many different genetic and environmental factors are involved.

Several genes have so far been linked with keratoconus often in specific populations. Although these genetic variants can influence a person’s risk of developing the condition, whether they do so is determined by complex interactions between other genes and environmental triggers.

Studying the function of these known risk genes is helping scientists to improve our understanding of the biology of keratoconus – and will hopefully lead to new prevention or treatment strategies. They have so far identified that these genes are involved in many diverse activities – including in eye development, the formation and structure of the cornea, the lattice of materials that fill spaces between cells, inflammation and in the control of cell growth. 

Scientists are also searching for environmental triggers that may contribute to the development of keratoconus. For example, around one-third of people with the condition also have an allergy. One theory is that allergies can cause itchy eyes – and this may lead to excessive rubbing over long periods of time, which could potentially weaken the cornea.

What are the signs and symptoms of keratoconus?

Keratoconus will typically begin in young people during their late teens or early 20s, with the changes in the eye slowly getting worse over time. Their symptoms will stabilise when the shape of their cornea stops changing, which usually happens around twenty years later.

A person’s eyesight will often be unaffected in the very early stages of keratoconus, although it may be slightly blurred and distorted. But as the condition progresses, their sight may become more distorted due to further bulging of their cornea. This will eventually lead to further short-sightedness and astigmatism – and so they will often need frequent changes to their spectacle or contact lens prescription to correct this. They may also have increased sensitivity to glare and might see halos around bright lights, which can affect their ability to drive at night. When the condition is more advanced, a person may have scarring of their cornea that can affect their ability to focus. 

Keratoconus can affect each eye differently. A person may initially only be affected in one eye but eventually, both of their corneas will develop the condition – although this may not be with the same severity.

How is keratoconus diagnosed?

An optician or ophthalmologist (hospital eye doctor) may perform several different tests to diagnose keratoconus. These include reading charts to check how well the eyes are focusing, as well as scans to measure the thickness and shape of the cornea. 

As the condition usually takes several months or years to develop, a person will usually be invited for repeat assessments to monitor any changes to the cornea over time.

How is keratoconus treated?

When keratoconus is in its early stages, a person’s eyesight can usually be corrected with spectacles or soft contact lenses. But when the condition becomes more advanced, rigid gas permeable contact lenses are usually required to correct their sight more adequately. 

Most people with keratoconus can achieve good sight wearing contact lenses. But in a few severe cases of keratoconus, a person may need a corneal transplant to correct their sight. This involves surgery to remove all or part of a damaged cornea and replace it with healthy tissue from a donor. Even after a corneal transplant, a person may still need to wear spectacles or contact lenses to correct their sight.

Newer treatments are becoming available that aim to stop the condition from getting worse. One of these is called ‘collagen cross-linking’, which involves removing a small area of the surface of the cornea, applying drops of vitamin B2 (riboflavin) followed by a burst of ultraviolet-A (UV-A) light. This is thought to cause tiny fibres in the cornea to join together, making it stronger. Another option is corneal implants – flexible plastic rings that are inserted into the edges of the cornea to try and flatten its shape. 

What research is underway into keratoconus?

One of Fight for Sight’s strategic programmes invests in research into eye diseases like keratoconus. 

Fight for Sight is currently funding Dr Mouhamed Al-Aqaba and his team of researchers at Nottingham University who are using biological ‘markers’ to investigate the underlying nerve structures in keratoconus. Fight for Sight also recently contributed to research at Guys Hospital and Moorfields Eye Hospital to understand more about the effectiveness of a new treatment for keratoconus called corneal cross-linking.

What can I do?

It’s important to have regular eye tests so that keratoconus is diagnosed as early as possible and for monitoring the progression of the condition. This will help ensure that you receive the right prescription to maintain good sight, as well as access to other potential treatments that may help stop your keratoconus from getting worse.

Have your eyes tested every two years even if you think your vision is fine. An eye test can spot some eye conditions and, if caught early, treatment may prevent further deterioration.

Last updated July 2019
Approved by Prof Chris Inglehearn, University of Leeds

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