Keratoconus (KC) is a condition in which the normally round shape of the cornea is distorted and a cone-like bulge develops, resulting in significant visual impairment. Its progression is generally slow and can stop at any stage from mild to severe. As it progresses, the cornea bulges and thins, becoming irregular and sometimes forming scars.
It is not one of the most common of eye diseases but it is by no means rare. It has been estimated to occur in I out of every 2,000 persons in the general population. The disease usually shows up in young people at puberty or in their later teen years. It is found in all parts of the world, with no known significant geographic, cultural or social pattern.
The first indication of KC to the patient is a blurring and distortion of vision that in the early stages may be corrected with glasses that require frequent changes in their astigmatism correction. The continued thinning of the cornea usually progresses slowly for 5 to 10 years and then tends to stop. Occasionally, it is rapidly progressive and, in the advanced stage, the patient may experience a sudden clouding of vision in one eye that clears over a period of weeks or months. This is called “acute hydrops” and is due to the sudden infusion of fluid into the stretched cornea. In advanced cases superficial scars form at the apex of the corneal bulge resulting in more vision impairment.
In the earliest stages of KC, ordinary eyeglasses may correct the mild myopia (near-sightedness) and astigmatism that is experienced. As the disease advances, gas-permeable contact lenses are the only way to correct vision adequately, and most of the time this is a permanent remedy. These must be fitted with great care and most KC patients need frequent checkups and frequent contact lens changes to achieve good vision and comfort.
Corneal collagen cross-linking with riboflavin (vitamin B2), better known as Cross-linking, is a parasurgical treatment for keratoconus. The cross-linking involves a one-time application of riboflavin solution to the eye that is activated by illumination with UV-A light for approximately 30 minutes. The riboflavin causes new bonds to form across adjacent collagen strands in the stromal layer of the cornea, which recovers and preserves some of the cornea's mechanical strength. The corneal epithelial layer is generally removed to increase penetration of the riboflavin into the stroma.
In only about 10% of KC cases a corneal transplant becomes necessary. In this process much of the central cornea of the KC patient is removed and is replaced with the cornea of a recently deceased person.