Keratoconus (literally “cone-shaped cornea”) is a non-inflammatory corneal dystrophy in which the normally dome-shaped cornea bulges outward. Initially this causes what is termed irregular astigmatism, and is observed as a blurring of vision or glare and streaking of lights at night, but if the bulging continues, the cornea becomes progressively thinner and weaker, and secondary complications can occur such as tearing and scarring within the cornea.
The causes of keratoconus are unknown. It tends to run in families but no definitive genetic cause has been identified, though several genes have been linked to the disease. Overall it occurs in about 1 in 2000 of the population but it is more prevalent in some geographical regions than in others, and has a higher incidence in Down’s patients and those who suffer from allergic conditions that lead to eye rubbing. Generally it is initially observed in the teenage years and it is rare for it to start after the age of about 40. It is believed that some unknown mechanism triggers the upregulation of enzymes that start to degrade the molecules within the tissue and cause the layers of the cornea to slide past one another. In an unaffected person, these molecules become chemically cross-linked, and thus stabilised, as a part of the ageing process and it is believed that this explains why the condition only develops in younger people.