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Keratoconus

Keratoconus, often abbreviated to "KC" and pronounced: KEHR-a-toh-kohn-nus, is a non-inflammatory eye condition in which the normally round dome-shaped cornea progressively thins causing a cone-like bulge to develop. This results in significant visual impairment. The cornea is the clear window of the eye and is responsible for refracting most of the light coming into the eye. Therefore, abnormalities of the cornea severely affect the way we see the world making simple tasks, like driving, watching TV or reading a book, difficult.

Early stages: In its earliest stages, keratoconus causes slight blurring and distortion of vision and increased sensitivity to glare and light. These symptoms usually first appear in the late teens and early twenties. The progression of KC is unpredictable. It is generally slow and can stop at any stage from mild to severe. As keratoconus progresses, the cornea bulges and thins, becoming irregular. Each eye may be affected differently.

Who gets Keratoconus?

The actual incidence of KC is not known. It is not a common eye disease, but it is by no means rare. It has been estimated to occur in 1 out of every 2,000 persons in the general population. Keratoconus is generally first diagnosed in young people at puberty or in their late teen's. It is found in all parts of the world. It has no known significant geographic, cultural or social pattern.

What are the signs and symptoms?

The first indication of KC to the patient is a blurring and distortion of vision. The continued thinning of the cornea usually progresses slowly for 5 to 10 years and then tends to stop. Occasionally, it is rapidly progressive. 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.

What causes Keratoconus?

KC has been known for at least two centuries, although it was not adequately described and distinguished from other similar corneal problems until the middle of the last century.

The causes of keratoconus are still unknown despite the long experience the ophthalmic community has had with it. There has been no shortage of speculation or study and numerous theories have been proposed.

One scientific view is that keratoconus is developmental (ie, genetic) in origin. This suggests that it is the consequence of an abnormality of growth, essentially a congenital defect. Another view is that KC represents a degenerative condition.
Still a third view is that KC is secondary to some disease process. A less widely held hypothesis suggests that the endocrine system may be involved. This idea gained credence from the usual appearance of the disease because it is generally first detected at puberty.

Heredity influences in KC are suggested by studies that show that approximately 13% of patients have other family members with the disease.

How is it treated?

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.

Contact lenses must be fitted with great care and most KC patients need frequent checkups and changes to achieve good vision and comfort. It should be noted that technological advances in both gas-permeable and soft lenses are being realised continually, offering more and more possibilities for those with keratoconus to achieve clear, comfortable vision.

In about 20% 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.

Eye banks in major cities collect healthy corneas to perform transplant surgery, which is quite common and usually very successful.

The probability of rejection is less than that of any other transplanted organ simply because the cornea has no blood supply. Rejection of other organs is usually due to incompatibility between the donor and the recipient and is mediated by blood cells.

While there is a 95% rate of success in corneal transplants for KC, this procedure, as with all operations, involves potentially serious risks. In cases where the first transplant is not successful, a second can be undertaken successfully. Recurrence of KC in the transplanted cornea has happened but is extremely rare.

Permanent loss of vision, though also extremely rare, can occur. Corneal transplantation is considered only in those cases in which contact lenses cannot be worn or provide inadequate vision -despite the most skilled efforts.

While the surgical transplantation of a new cornea will resolve the basic problem of corneal surface irregularity, eyeglasses/contact lenses are usually needed for vision correction. In many cases rigid gas permeable (RGP) contact lenses will be required to correct the large amount of corneal distortion that is sometimes associated with the transplant regardless of the skill of the surgeon.

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