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Keratoconus, 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 and visual symptoms such as light glare and halo as well as double or triple vision. 



Multiple Images from Keratoconus Visual Static    Night Glare from Keratoconus Light Scatter


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.

What Causes Keratoconus?

The actual cause of keratoconus is unclear. It may have a genetic, inheritable component. 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 because early treatment can prevent progression of the condition over time.

Keratoconus is typified by corneal thinning and biomechanical instability. This may be caused by abnormalities in the normal collagen structure of the cornea. Collagen is the main structural component of the cornea. Collagen is a 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.  Weakness of the corneal structure causes keratoconus and its progression over time. 

The normal cornea is made of pancakes (or lamellae) of collagen tissue in a complex array. In keratoconus, the collagen lamellar architecture may be abnormal.  A complex arrangement of these pancakes and the extracellular matrix of biologic sugars maintains optical shape and structural integrity in the normal cornea.  Interweaving of the collagen lamellae and linkages between molecules give the cornea its strength.  Around the edge of the cornea, the collagen bands change to a circular belt, providing additional support to the round corneal architecture.  Finally, transverse-oriented lamellae insert into the front layers of the cornea (Bowman’s layer), acting as roots to further support corneal structure.  This complex micro-organization is altered in keratoconic corneas.  In KC, the collagen fibrils are unevenly distributed, with rearrangement of their normal conformation.  The keratoconic cone, itself, is most affected with loss and distortion of collagen fibers.  In addition, KC corneas show less interweaving of the collagen pancakes and decreased in the collagen anchors supporting the corneal structural shape.   These changes may allow the collagen pancakes to split and slide on one another and exacerbate KC progression. Because of this, it is important that you do not rub your eyes in order to avoid actual mechanical shearing of the collagen pancakes. 

Collagen "Pancakes" Span the Cornea     Anchoring Fibers    Interweaving Collagen     Circular Bands

What causes the changes that we see in the corneal structure in keratoconus? There may be a primary biochemical event that triggers these changes, and, in some cases, these in turn may have a genetic predisposition.  There are enzymatic changes associated with KC.  In particular, there may be an increase in collagen and extracellular matrix breakdown cause by enzymes such as matrix metalloproteinases (MMP) and others.  In addition, enzymes such as lysyl oxidate (LOX), which help the formation of mature collagen by creating natural crosslinks, may be low in keratoconus.

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