Keratoconus is an eye condition in which the cornea develops a conical shape, distorting and blurring vision. It has various causes and about one in 10 cases is inherited. Various treatments can help slow its progress and vision loss can often be restored by a corneal transplant.
 

How does keratoconus develop?
The cornea, the outermost layer of the eye, is usually a regular round shape. If you develop keratoconus, the middle of your cornea becomes thinner and gradually bulges outwards. Eventually, the cornea forms a rounded cone shape, producing distorted vision and short-sightedness. Both eyes are usually affected by keratoconus but not always equally.
 

The astigmatism and short-sightedness caused by keratoconus gets worse over time in 20% of patients, as the cornea continues to change shape. Vision can deteriorate suddenly if the inner membrane just under the cornea splits and allows a larger volume of fluid into the stroma, the main layer of the cornea. Swelling of the stroma can be painful, and it can cause corneal scarring as well as a reduction in vision.
 

Keratoconus is an eye disease of young people; symptoms usually start at around puberty and progress through the teens and 20s, with the greatest impact experienced by people aged 21-30. Some people experience several years where their cornea remains stable, others deteriorate quickly. Prompt treatment can delay the progression of keratoconus but when the condition has deteriorated significantly the only treatment that can restore reasonable visual acuity is a corneal transplant. This happens in about 20% of people with keratoconus.
 

What are the symptoms of keratoconus?
The first symptom of keratoconus is usually blurred vision, sometimes with increased sensitivity to bright light or ghost or halo effects or multiple images. Teenagers start by having a routine eye check-up, which identifies the change in shape of the cornea in some cases.
 

In others, an initial diagnosis of short-sightedness or astigmatism is made but frequent changes in the prescription for glasses or contact lenses usually alerts an optician to the possibility of keratoconus, and he or she makes a referral to an ophthalmologist. Keratoconus is then diagnosed and treatment can be started.
 

What causes keratoconus?
Keratoconus is a type of corneal dystrophy that affects between one in 1,000 and one in 500 people in the general population. Several different factors may contribute to its development:

  • Genetics: around one in 10 people with keratoconus have a family history of the disease. Keratoconus is associated with genetic conditions such as Down’s syndrome and Marfan syndrome. Research suggests that keratoconus is likely to be a complex genetic disease, not one that is due to a single gene mutation.
  • A weakness in the collagen supports that maintain the structure of the cornea. People with connective tissue disorders are more prone to keratoconus. The layers within the stroma of the cornea are thought to lack sufficient cross links, which makes them unable to hold their usual structure, allowing the change in shape to form a cone.
  • Allergies, particularly those that affect the eyes, or atopic diseases such as asthma.
  • Other eye diseases including vernal keratoconjunctivitis.
  • Metabolic and chemical changes in the cornea due to unknown causes.