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KeratoconusKeratoconus, one of the more obscure and less widely known eye diseases, occurs in about one out of every 1,000 individuals. In fact, as we develop better screening tools, it is likely that many more are affected.  It is also one of the more difficult eye diseases to diagnose. The disease results in thinning and weakening of the cornea, the clear lens that is the front of your eye (like the crystal on a watch). As a result, the cornea bulges out of its smooth, dome-like structure, and assumes a more conical and irregular configuration. Because of this change in shape, the cornea loses its ability to form a clear image in the eye and the patient's vision can decrease drastically. Why is this? Optically, in the keratoconic cornea, light is not completely focused because of the corneal distortion. This causes scattering of light rays and the formation of "visual static", much like the static that you may find on a TV. This distortion, and consequent visual static, can increase over time, with decrease in vision.  Please see the videos below and at the bottom of the page for a short overview of keratoconus by Dr. Hersh.

Biologically and structurally, the cornea is made up of pancakes (lamellae) of collagen protein which are “glued” together by natural biologic sugars (called glycosaminoglycans or GAG’s). Both the collagen and microstructure of the cornea are abnormal in keratoconus, causing a weakness of the corneal structure which then leads to optical problems. It is a progressive condition which, aside from distorting the cornea's natural optics, can also lead to scarring and other problems.

The presentation and impact of keratoconus can vary widely from person to person. In its earliest stages, keratoconus often masquerades as astigmatism or nearsightedness, two of the more common eye conditions. Often, it is only after numerous unsuccessful attempts at vision correction with glasses or soft contact lenses that your doctor may look elsewhere for a diagnosis.

KeratoconusWhat Causes Keratoconus?

The actual cause of keratoconus is unclear. It may have a genetic, inheritable component. Several gene loci have been identified which might have an effect on KC.  However, in many patients there are no family members with the disease. Similarly, most children of KC patients do not have keratoconus, but they should be checked in early adolescence for signs of KC.

Keratoconus is typified by corneal thinning and biomechanical instability.  There are 2 principle theories of keratoconus development.  The first is structural.  Here, KC may be caused by abnormalities in the normal collagen structure of the cornea. Collagen is the main structural component of the cornea. It is a fiber-like molecule that typically is very strong. For example, it makes up most of the structure of the tendons and ligaments of your muscles and bones. The cornea is made of pancakes of collagen tissue in a complex array. In keratoconus, the collagen lamellar architecture may be abnormal. It appears that a primary event in KC leads to the loss and/or slippage of callagen fibrils and changes to the gluelike matrix of the cornea, leading to corneal weakening and, ultimately, progressive distortion.

The second basic theory behind keratoconus development is enzymatic.  There may be an increase in enzymes (called proteases) which degrade corneal collagen.  On the other hand, there may be a lack of enzymes, such as lysyl oxidase, which help to form linkages between the collagen pancakes and the surrounding molecules. In addition, the cells of the cornea (keratocytes), may not be normal, and may contribute to the thinning and instability of the keratoconic cornea.

In keratoconus, the linkages of the collagen molecules and lamellae to one another may  be weak and diminished. For instance, "anchoring fibrils" which normally lock the collagen pancakes to the front of the cornea, or Bowman's layer, may be abnormal. This may allow the collagen pancakes to slide on one another and exacerbate KC progression. Because of this, it is important that the keratoconus patient does not rub his/her eyes in order to avoid mechanical shearing of the collagen pancakes.

KeratoconusFinally, Inflammation may also play a role in keratoconus. Reactive oxygen species, or oxygen free radicals, may damage the corneal cells and collagen structure, and lead to keratoconus progression. Because of this, avoiding and treating eye inflammation (for instance, eye allergies) also may be important for the patient with KC.

Here at the CLEI Center for Keratoconus, we are working to identify factors that might place the keratoconus patient at greater risk, while we endeavor to bring our patients the best treatment options available.



About CLEI Center for Keratoconus