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.
Keratoconus is estimated to affect between one in 500 to 2,000 people worldwide. But it may be more common in certain populations.
Different types of keratoconus
There are four main types of keratoconus, in addition to rarer variations of the disease.
- Round cone keratoconus: Round cone keratoconus affects a relatively small area of the cornea, however the steepness of the affected area can be extreme.
- Oval keratoconus: Oval or sagging cone keratoconus affects a larger portion of the cornea. It can cause rupturing (or hydrops) of the cornea's internal membranes and scarring, as well as making it harder to fit contact lenses.
- Forme fruste keratoconus (FFK): The most common type of keratoconus. It is also the most mild. FFK is usually symptom-free and only diagnosed by mapping the surface of the eye. In FFK the disease starts, but for some reason it stops progressing without any need for treatment.
- Keratoglobus keratoconus: Keratoglobus differs from keratoconus. Instead of a single point of thinning of the cornea (which results in a bulging and the development of a cone), the cornea in people with keratoglobus is thin everywhere.
- Posterior keratoconus: A rare, usually congenital corneal disorder where there is a small region with an increase in curvature at the back of the corneal surface. It is unrelated to the other forms of keratoconus.
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. 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.
Understanding the biology of keratoconus
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 the cells of the cornea, inflammation and in the control of cell growth.
Learning about the development of keratoconus
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 eye rubbing over long periods of time, which could potentially further weaken the cornea.
Keratoconus is also thought to involve a defect in the structure of collagen, the tissue that makes up most of the cornea.
Is Keratoconus genetic?
Most people who develop keratoconus have no family history of the condition, and they are otherwise well. But keratoconus can occasionally 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.
- Dr Nasser Siabi, OBE, is one of five brothers. Of those, four had keratoconus. Listen to the podcast where he discusses his family history and talks about assistive tech.
What are the signs and symptoms of keratoconus?
Keratoconus will typically begin in young people during their 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 blur the vision further.
Keratoconus can affect each eye differently. A person may initially only be affected in one eye but eventually, both of their corneas usually develop the condition – although this may not be with the same severity.
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 fully correct their sight.
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 almost always still needs to wear spectacles or contact lenses to correct their vision.
Newer treatments have become available 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 the tiny collagen 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.
Based on research there are the following treatments for keratoconus:
- Corneal crosslinking
This is an option if keratoconus is detected at an early stage when it is still progressing. Collagen is an important substance that holds the cornea together. Crosslinking is thought to bind the collagen fibres of the cornea to stop further deterioration. It does not reverse existing changes.
Custom soft contact lenses
Custom soft contact lenses are intended for mild to moderate keratoconus. Lenses need to be replaced every three to six months depending on the material and each individual’s reaction to the lens. Soft lenses are easier to get used to than corneal gas permeable lenses but unfortunately might not give such a crisp image.
Rigid Gas permeable (RGP) contact lenses
Hard lenses are made of a material which allows oxygen to pass through it. RGP lenses are often a little uncomfortable at first but this becomes less as time goes by. If discomfort continues other types of contact lenses can be considered.
"Piggybacking" contact lenses
The piggyback system consists of a rigid gas permeable (RGP or GP) lens sitting on top of a soft contact lens. This combination can lead to clear vision without the discomfort that patients can feel wearing hard lenses. The soft contacts act as a shield and a cushion to provide additional comfort. Piggybacks can be costly, as this can involve two different cleaning systems and soaking solutions.
Hybrid contact lenses
Lens where the centre is a rigid contact lens (to offer best vision) and the outer part is a soft contact lens, to offer more comfort. These lenses can be difficult to fit and many patients find them very difficult to put in and take out.
Scleral and semi-scleral lenses
Scleral lenses are larger diameter lenses that lie on the white part of the eye (the sclera) and floats above the cornea without touching its surface. Patients with advanced keratoconus or extremely protruding cones could benefit from this option. In general, these lenses are very comfortable to wear and provide excellent vision in select patients who cannot tolerate other types of lenses.
Corneal ring implants
Corneal ring implants (eg. Intacs) are thin plastic, semi-circular rings that are inserted into the mid layer of the cornea. A topical anesthaetic is used to perform the procedure, which helps to reshape the cornea by flattening it to improve vision. This can improve uncorrected vision in most patients, however, glasses or contact lenses may still be needed for functional vision. Those who should not undergo the procedure include: Pregnant women, people who have other eye health problems that may cause future problems, or people taking certain medication that may impair healing of the eye.
Topography-guided conductive keratoplasty
A non-invasive that uses radiofrequency to send radio waves to specific areas on the cornea. This is administered by a handheld probe and could be effective in reshaping corneal configuration in eyes with keratoconus.
Often referred to as keratoplasty or a corneal graft, a cornea transplant is an operation to remove all or part of a damaged cornea and replace it with healthy donor tissue. Keratoconus is one of the most common reasons for a cornea transplant. The procedure can be carried out under general anaesthetic or local anaesthetic. It usually takes less than an hour and patients either leave the hospital the same day or stay overnight. It can take 12-18 months for the vision to fully recover and further surgery may be required to achieve the best visual outcome.The type of cornea transplant you have will depend on which part of the cornea is damaged or how much of the cornea needs replacing. The options include:
- penetrating keratoplasty (PK) – a full-thickness transplant
- deep anterior lamellar keratoplasty (DALK) – replacing or reshaping the outer and middle (front) layers of the cornea
Laser vision correction is contraindicated if there is keratoconus.
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 Veronique Vitrat and her team at the University of Edinburgh who are investigating corneal thinning to ultimately reduce increasing demand on corneal transplants. The focus of the study will be on keratoconus as well as Brittle Cornea Syndrome (BCS), a rare but devastating genetic disorder.
Previously, the charity has funded 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 previously contributed to research at Guy's Hospital and Moorfields Eye Hospital to understand more about the effectiveness of a new treatment for keratoconus called corneal cross-linking.
Is there a cure for keratoconus?
Currently there is no cure for keratoconus, although cross linking can prevent further progression if the disease is detected early. There are tools to manage the condition. In the early stage of keratoconus, glasses can be used to give a good standard of vision. Different contact lenses are considered as keratoconus progresses and the cornea becomes more irregular in shape. Each patient’s contact lens fit can change over time. Optometrists can help patients in choosing the best kind and ordering a new type of contact lens if required.
Think you have Keratoconus? Here's what to 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 collagen cross-linking which 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 November 2022