The word keratoconus is derived from two Greek words: kerato, meaning cornea, and konos, meaning cone. Keratoconus, therefore, 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. In simple terms, this means that the cornea, instead of being round like a basketball, is oblong like a football. This distortion usually begins in the late teens or early twenties and goes through a period of progression that can last five to 15 years or longer. As the keratoconus progresses, the cornea bulges and thins, becoming irregular and sometimes forming scars. Once the progression ceases, the patient's corneal shape is then stable for the remainder of his or her lifetime. The end result may range from mild ectasia (bulging) with minimal patient symptoms to severe disease with significantly decreased vision.
What causes Keratoconus?
Although we are very familiar with the way that keratoconus behaves clinically, we still are not able to fully explain why these corneal changes occur in a given individual. By and large, the causes of keratoconus are still unknown. There are however, several theories that may give us some insight. One scientific view is that keratoconus is developmental or genetic in origin. In some families, the hereditary pattern follows a strict Mendellian pattern, while in other families a hereditary pattern is absent or incomplete. It is generally thought that only 10% of families are at risk for more than one member being affected. Newer, more sensitive diagnostic methods, however, may prove that this percentage underestimates the true familial tendencies of keratoconus. Another theory is that keratoconus represents a degenerative condition. Many individuals with keratoconus are eye rubbers, which some believe can lead to corneal degeneration and resultant ectasia. Still a third postulation is that keratoconus is secondary to some disease process. This idea probably stems from the fact that keratoconus is slightly more common in eyes of Down's Syndrome patients and those with Atopic Skin Disease than in other individuals. However, it should be emphasized that the overwhelming percentage of keratoconus patients are free from other ocular or systemic diseases.
Who is susceptible to keratoconus?
The actual incidence of keratoconus is not known. 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 one out of every 2,000 persons in the general population. As previously noted, this disease usually shows up in young people at puberty or in their later teen years. It is found in all parts of the United States and the rest of the world, with no known significant geographic, cultural or social pattern.
Signs and Symptoms
The first indication of keratoconus to the patient is a blurring and distortion of vision that, in the early stages, can be corrected with glasses. Often times the spectacles require frequent changes (as the disease progresses). The continued thinning of the cornea usually progresses slowly for five to 15 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.
How is Keratoconus Treated?
In the mildest cases of keratoconus, ordinary eyeglasses may correct the near-sightedness and astigmatism caused by this ectasia. However, gas-permeable contact lenses are the mainstay to correct vision adequately if it progresses. Once contact lens wear becomes necessary, it is a lifelong treatment modality. These must be fitted with great care, and most keratoconus patients need frequent checkups and frequent contact lens changes to achieve good vision and comfort. In some instances, the use of one lens on top of another (so-called piggybacking), combination soft and hard lenses (hybrid contact lenses), or large diameter hard lenses (scleral contact lenses) provide an alternative solutions. It should be noted that technological advances in both gas-permeable and soft lenses are made constantly, offering more and more possibilities for keratoconus patients. The goal of contact lens wear in keratoconus patients is to maintain wear as long as the patients' visual acuity remains at an acceptable level, good ocular comfort is maintained and wearing time adequate for the individual is being realized. If these goals are not being met, then surgical options need to be considered (see our testimonial page to learn more).
INTACS® prescription inserts are used for keratoconic patients who are contact lens intolerant or patients who are unable to achieve suitable vision with glasses or contacts. Placing INTACS® in the periphery of the cornea causes the center of the cornea to flatten to a more normal dome shape. The goal of INTACS® is to provide the patient with improved functional vision and better comfort with contact lenses or glasses. In many cases, INTACS® can delay or even eliminate the need for cornea transplant.
As part of the CXLUSA study protocol, our practice can also offer Corneal Collagen Crosslinking (CXL) as an alternative treatment for patients with mild to moderate, progressive keratoconus. This is a transepithelial (epithelium-on) method for strengthening the corneal collagen and preventing further progression of the disease. For more information visit the CXLUSA study website.
In only about 15% of keratoconus cases does a corneal transplant become necessary. In this process much of the central cornea of the patient is removed and is replaced with the cornea of an organ donor. Eye banks across the country harvest healthy corneas from decedents and fulfill requests from eye surgeons for these corneas. Corneal transplantation for keratoconus is successful about 90% of the time. The major risks of the surgery include hemorrhage, infection, and organ rejection. 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, RGP contact lenses will be required to correct the large amount of corneal distortion that is sometimes associated with the transplant.