Symptoms and Signs
Keratoconus can be difficult to detect, because it usually develops so slowly. However, in some cases, it may proceed rapidly. As the cornea becomes more irregular in shape, it causes progressive nearsightedness and irregular astigmatism to develop, creating additional problems with distorted and blurred vision. Glare and light sensitivity also may be noticed. Keratoconic patients often have prescription changes every time they visit their eye care practitioner. It's not unusual to have a delayed diagnosis of keratoconus, if the practitioner is not familiar with the early-stage symptoms of the disease.
What Causes Keratoconus?
New research suggests the weakening of the corneal tissue that leads to keratoconus may be due to an imbalance of enzymes within the cornea. This imbalance makes the cornea more susceptible to oxidative damage from compounds called free radicals, causing it to weaken and bulge forward.
Risk factors for oxidative damage and weakening of the cornea include a genetic predisposition, explaining why keratoconus often affects more than one member of the same family. Keratoconus is also associated with overexposure to ultraviolet rays from the sun, excessive eye rubbing, a history of poorly fit contact lenses and chronic eye irritation.
In the mildest form of keratoconus, eyeglasses or soft contact lenses may help. But as the disease progresses and the cornea thins and becomes increasingly more irregular in shape, glasses or soft contacts no longer provide adequate vision correction.
Treatments for moderate and advanced keratoconus include:
Gas permeable contact lenses: If eyeglasses or soft contact lenses cannot control keratoconus, then rigid gas permeable (RGP) contact lenses are usually the preferred treatment. Their rigid lens material enables RGP lenses to vault over the cornea, replacing the cornea's irregular shape with a smooth, uniform refracting surface to improve vision.
But RGP contact lenses can be less comfortable to wear than a soft lens. Also, fitting contact lenses on a keratoconic cornea is challenging and time-consuming. You can expect frequent return visits to fine-tune the fit and the prescription, especially if the keratoconus continues to progress.
"Piggybacking" contact lenses: Because fitting a gas permeable contact lens over a cone-shaped cornea can sometimes be uncomfortable for the individual with keratoconus, some eye care practitioners advocate "piggybacking" two different types of contact lenses on the same eye. For keratoconus, this method involves placing a soft contact lens, such as one made of silicone hydrogel, over the eye and then fitting a GP lens over the soft lens. This approach increases wearer comfort because the soft lens acts like a cushioning pad under the rigid GP lens.
Your eye care practitioner will monitor closely the fitting of "piggyback" contact lenses to make sure enough oxygen reaches the surface of your eye, which can be a problem when two lenses are worn on the same eye. However, most modern contacts — both GP and soft — typically have adequate oxygen permeability for a safe "piggyback" fit.
Hybrid contact lenses: Hybrid contact lenses have a relatively new design that combines a highly oxygen-permeable rigid center with a soft peripheral "skirt." Manufacturers of these lenses claim hybrid contacts provide the crisp optics of a GP lens and wearing comfort that rivals that of soft contact lenses. Hybrid lenses are also available in a wide variety of parameters to provide a fit that conforms well to the irregular shape of a keratoconic eye