What is Keratoconus
The cornea is the window of the eye. Light travels through the cornea past the lens to the retina and then the brain to form a visual image. The normal corneal surface is smooth and aspheric i.e. round in the center, flattening towards its outer edges. Light rays passing through it moves in an undistorted manner to the retina to project a clear image to the brain.
In patients with keratoconus the cornea is cone shaped (hence the name keratoconus, derived from the greek word for cornea (‘kerato’) and cone shaped (‘conus’). In patients with keratoconus the cornea is not only cone shaped but the surface is also irregular resulting in a distorted image being projected onto the brain.
Because the cornea is irregular and cone shaped, glasses do not adequately correct the vision in patients with keratoconus since they cannot conform to the shape of the eye. Patients with keratoconus see best with rigid contact lenses since these lenses provide a clear surface in front of the cornea allowing the light rays to be projected clearly to the retina. Hence the vast majority of patients are treated with rigid contact lenses. There are however some excellent new surgical options for patients with keratoconus who cannot tolerate these lenses, these options are discussed under treatments for keratoconus.
Many patients are initially unaware they have keratoconus and see their eye doctor because of increasing spectacle blur or progressive changes in their prescription. In many instances even a good refraction yields poor vision. Keratoconus is most often diagnosed by a cornea specialist who my see typical findings when examining the patient at the slit-lamp. In early forms of the disease there may be no obvious finding on slit-lamp evaluation and the diagnosis is made by computerized videokeratography only.
Keratoconus typically commences at puberty and progresses to the mid thirties at which time progression slows and often stops. Between age 12 and 35 it can arrest or progress at any time and there is now way to predict how fast it will progress or if it will progress at all. In general young patients with advanced disease are more likely to progress to the point where they may ultimately require some form of surgical intervention.
Keratoconus may occur in one eye only initially but most commonly affects both eyes with one eye being more severely affected than the other. Both males and females are equally affected and there is no ethnic predilection though in some parts of the world such as New Zealand and in certain parts of Finland there is a higher incidence due to genetic factors.
Despite millions of dollars being spent on keratoconus no one truly knows the cause of the disease. There have been many interesting theories but none of them have been proven conclusively neither have any of them consistently been reproduced by multiple research groups. For example one theory suggests that there is deficient collagen crosslinking caused by free radicals but there is no scientific reproducible evidence to support such a theory. Others suggest that eye rubbing causes the progression of keratoconus. The evidence for this is however anecdotal based on several case reports, but again there is no reproducible scientific evidence to support this.
Our research group was the first group to demonstrate that genetic factors play a major role in the development of keratoconus (Wang Y, Rabinowitz YS, Rotter J, Yang H. Genetic epidemiological study of keratoconus: evidence for a major gene determination. American Journal of Medical Genetics 93:403-409,2000). While our scientific based evidence supports a role for genetic factors this does not mean if you have a child with keratoconus they will necessarily develop keratoconus, since only 13-15% of keratoconus patients have a family history with keratoconus. It does mean however that genes play a role in its development and suggests that any proposed treatment for the disease will either be very temporary or short lived until the genes that contribute to its development are identified and either replaced or suppressed. This is the only potential hope for a permanent cure to stop progression and ensure the cornea will no longer continue to thin.For a comprehensive scientific review on keratoconus click the link below to read a PDF version of the following article: (Rabinowitz YS. Keratoconus: update and new advances.(Major review). Survey of Ophthalmology. 1998: 42:4:297- 319.)