Keratoconus 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. KC is caused by 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. Furthermore, this irregularity of the corneal optics and visual perturbations progress over time.
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.
Like static on a TV, non-focused light in KC causes “visual static” which causes glare and multiple vision
The presentation and impact of keratoconus can vary widely from person to person. Usually, it is first detected in a patient’s teens or twenties. 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.
Collagen lamellae (“pancakes”) create corneal superstructure
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.
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.
Assessing Your Keratoconus
In order to fully assess your keratoconus, understand the likely future course of the disease, and make appropriate treatment recommendations, an extensive eye examination is performed along with several specialized tests to fully analyze your problem. These tests also give you a complete baseline for your ongoing care in the future.
There are a number of goals of the comprehensive keratoconus evaluation at the CLEI Center for Keratoconus. First, we want to fully assess and define your keratoconus in order to monitor progression over time. Second, this testing will allow us to best recommend a course of treatment to optimize your visual function.
The CLEI Center for Keratoconus incorporates all of the latest diagnostic technologies to assess your KC and determine the proper course of treatment. Some of these diagnostic tools include:
Computerized Corneal Topography Analysis:
Corneal topography instruments assess your cornea’s optical surface. These are corneal maps that can assess many indices of your individual corneal shape and structure. We use a number of instruments, each of which may give different clues to the corneal shape, including the Pentacam, Topolyzer, and EyeSys units. Corneal topography is analagous to looking at a mountain range from a satellite. A normal cornea is green (like a gentle slope). Red is a higher point (like a mountain), and can indicate keratoconus. Blue is a lower point (like a lake). In some cases of keratoconus, your corneal topography map can be used to help program a laser for topography-guided PRK treaments.
Keratoconic “cone” is seen as the red elevation on the topography map
Corneal Ocular Coherence Tomography (OCT):
Ocular Coherence Tomography is analagous to an MRI of your cornea. It gives cross-sectional, magnified pictures of your cornea from which we can study all of the corneal layers. OCT allows us to map your corneal thickness in detail.
Wavefront analysis assesses the eye’s optical system and aberration profile. Because of the optical irregularities of the keratoconic cornea, light is not completely focused. This causes scattering of light rays and the formation of “visual static”, much like the static that you may find on a TV. Wavefront analysis defines the particular types of static that are present in the keratoconic cornea. It is analogous to using a computer to check for any static on your TV.
Corneal Biomechanics Measurements:
The Optical Response Analyser (ORA): is a new instrument which measures the elasticity and flexibility of the cornea and is the first true clinical measurement of corneal biomechanics in KC. This may allow for better diagnosis of early keratoconus, help to predict its possible progression, and allow for monitoring of changes in the keratoconic cornea.
Corneal thickness (ultrasonic and optical pachymetry) measurements detect the degree to which a keratoconus cornea is thinned. In KC, the cornea is thinner and weaker than normal. Changes over time can be monitored by periodic assessment of the corneal thickness measure both by ultrasound and by optical imaging on the Pentacam unit.
Living with Keratoconus
There are some general precautions that a patient who has keratoconus can take to help decrease the chance of disease progression.
1) Don’t rub your eyes.
This is probably the most important suggestion. Remember that KC is a problem of corneal mechanics and strength. The cornea gets its strength from the linkages of the collagen pancakes to one another. Eye rubbing may exacerbate slipping of the the collagen pancakes of the cornea and possibly cause further destabilization of the corneal structure. It can also irritate the eyes, causing inflammation that is not good for the keratoconic cornea.
2) Control eye allergies.
Ocular allergy can cause inflammation, and also encourage eye rubbing. Therefore, use medications and drops as prescribed by your doctor to minimize symptoms of eye allergy.
3) Optimize your contact lens fit.
The impact of contact lens wear on progression of keratoconus is unclear. Contact lenses are the mainstay of keratoconus treatment in many cases. Making sure that the contact lens fit is the best possible, will avoid problems secondary to irritation, inflammation, or mechanical trauma to the cornea.
4) Wear sunglasses in bright sun.
Ultraviolet light may increase the formation of inflammatory molecules which can further damage the corneal structure So, wear UV protecting sunglasses when you are going to get alot of sun exposure.
5) Eat a good diet
Diets high in antioxidants (found in green, leafy vegetables and colored vegetables such as tomato and pepper)) may combat some of the inflammatory mediators that can exacerbate KC progression. Antioxidant vitamin and omega 3 supplements may also be helpful.