The clear window at the front of your eye (the cornea) is usually an even round shape. In keratoconus, the cornea gradually thins and forms a cone-shaped bulge, resulting in progressive blurring of vision. This condition is relatively common, affecting up to 1 in 1000 people.
What causes Keratoconus
The underlying problem in keratoconus is a biomechanical weakness in the supporting collagen fibres of the cornea. This weakness allows the cornea to bulge forward, distorting its normal shape and causing irregular astigmatism.
The exact cause of keratoconus is still uncertain although it is believed to be partly genetic and occurs more commonly in people with allergies like asthma or eczema. There is also an association between eye rubbing and keratoconus.
How keratoconus affects your vision
The cornea allows light to enter the eye and provides focus so that a clear image can be seen. When the cornea loses its shape from keratoconus, your vision becomes blurred because the cornea cannot focus light properly. Advanced keratoconus can also cause scarring of your cornea, which can severely decrease your vision by distorting focus and reducing the amount of light that can enter your eye.
A small number of patients may experience sudden, painful loss of vision if fluid from the inside the eye enters the thin cornea. This is called hydrops and often leaves a scar in the cornea after it resolves.
Natural history of keratoconus
Keratoconus is often diagnosed in young people in their teens or twenties. In 20% of cases, the condition is progressive and can get worse with time. For most people however, it stops progressing in their mid to late thirties due to natural age-related stiffening of the cornea.
In the early stages or in mild forms of the disease, glasses alone may be sufficient to provide good vision. In more advanced disease, special contact lenses are usually required to correct for the irregular astigmatism. However, in severe cases, where glasses or contact lenses alone are not able to provide adequate vision correction, there are now several treatments available to help with this condition including laser treatment combined with cross-linking, intracorneal rings (Kerarings), implantable collamer lenses and corneal transplantation.