The term, “Keratoconus” refers to an eye condition involving the cornea, the clear window at the front of the eye, thinning and warping into a cone-like bulge. This condition can do a great deal of harm to your vision. Normally the cornea maintains a curved, dome-like shape. This allows the cornea to refract light onto the back of the eye, in such a way that it creates a clear image to send to the brain where it is interpreted. When the cornea takes on a more conical shape, this scatters the light as it comes in, sending light to several different points on the retina, creating blurring of vision, distortion of vision, increased sensitivity to light, glare and mild eye irritation.
Puberty is generally when keratoconus begins to emerge. It begins with mild astigmatism and myopia. Although it usually affects both eyes, symptoms may be different in each individual eye. Usually keratoconus progresses quite slowly, getting worse over the course of roughly 10 or 20 years and then ceasing abruptly.
Scientists are not sure what, exactly, causes a person to develop keratoconus. However, many studies seem to indicate that it is linked to genetics. This is based on statistics that 10% of all people who develop keratoconus have a previous family history of the condition. Excessive eye rubbing and other similar eye injuries, as well as certain eye diseases such as retinopathy of prematurity, and systemic diseases such as down syndrome also seem to be linked to the development of keratoconus.
Keratoconus can often be discovered during the course of a routine eye exam, through tests that help to determine the exact shape of the cornea. A slit-lamp examination is the most popular test used to diagnose keratoconus. This test involves your eye doctor directing a vertical beam of light onto your eye, then using a low-powered microscope to look at your eye to evaluate the shape of your cornea. Optical scanning techniques, such as optical coherence tomography and corneal topography may also be used to create a digital topography map of your cornea's surface and measure the thickness of the cornea.
Treatments for moderate to advanced keratoconus include:
Gas permeable contact lenses. If eyeglasses or soft contact lenses cannot control keratoconus, then gas permeable (GP) contact lenses are usually the effective. Rigid materials enable the GP lenses to dome over the cornea, replacing the irregular shape with a smooth, uniform refracting surface thus improving vision.
There is a comfort cost though because GP contact lenses can be less comfortable to wear compared to soft lenses. Fitting of the contact lenses on keratoconic corneas are also challenging and more time-consuming. Expect frequent office visits for fine-tuning and fitting of the prescription, especially as the keratoconus continues to progress.
Piggybacking lenses. Some practitioners advocate “piggybacking” two different types of contact lenses on the same eye to better fit the gas permeable contact lens over the cone-shaped cornea. Some patients may find this a bit uncomfortable. The GP lens is fitted on top of the soft contact lens which sits on the eye. The approach is thought to increase patient comfort as the soft lens acts as a cushion under the rigid second lens, the GP lens.
Hybrid contact lenses. Hybrid contact lenses are a relatively new design combining highly oxygen-permeable rigid center with a soft peripheral lens “skirt.” Manufacturers claim their hybrid contacts provide crisp optics of GP lenses alongside wear- comfort rivaling soft contact lenses. Hybrid lenses are available in a wide variety of parameters to provide optimal fit which conforms best to the irregular shape of a keratoconic eye.
Scleral and semi-scleral lenses. These are gas permeable contact lenses which have a large diameter allowing the edge of the lenses to rest on the white part of the eye -the sclera. These lenses will also dome over the irregularly shaped cornea, allowing for a most comfortable fit. They will move less during eye blinks. Scleral lenses cover a larger portion of the sclera, whereas semi-scleral lenses cover a smaller white (eye) area.
Intacs. These are tiny plastic inserts which are surgically inserted just underneath the eye surface in the periphery of the cornea helping to reshape the cornea. The result, clearer vision. Intacs may be advised when keratoconus patients no longer can obtain functional vision with contact lenses or eyeglasses.
Studies show that Intacs can improve the spectacle-corrected visual acuity (BSCVA) of a keratoconic eye by an average of two additional lines on a standard eye chart. The implants have the additional advantage of being removable and changeable. The surgical procedure takes 10 minutes. Intacs might delay but will not prevent the required corneal transplant, if keratoconus progresses.
Corneal crosslinking. This procedure, “CXL” for short, strengthens corneal tissue slowing or preventing the bulging of the eye surface. In turn this procedure can reduce the need to undergo a corneal transplant.
There are two types of corneal crosslinking: epithelium-off and epithelium-on. Epithelium-off crosslinking is where the outer portion of the cornea (epithelium) is removed to allow entry of riboflavin, a B vitamin, to the cornea. Once administered, the riboflavin is activated with UV light. With the epithelium-on method (transepithelial crosslinking), the corneal surface is left intact.
Neither procedure is FDA-approved. However, multiple clinical trials are currently underway. Although cross-linking may already be common in some countries — few doctors in the United States will perform the procedure until it is FDA-approved. For that reason, it’s also not covered by insurance. The procedure costs $2,500 per eye, not including the contacts or eye drops.
Corneal transplant. Some people with keratoconus cannot tolerate a rigid contact lens, or they are beyond the point of contact lenses or known therapies providing acceptable vision. The last resort remedy may be a corneal transplant, also called a penetrating keratoplasty (PK or PKP). Note that after successfully completing a cornea transplant, most keratoconic patients will still need glasses or contact lenses for clear vision.