Keratoconus is a progressive disease, often appearing in the teens or early twenties, in which the cornea thins and changes shape. The cornea is normally a round or spherical shape, but with keratoconus the cornea bulges, distorts and assumes more of a cone shape. This affects the way light enters the eye and hits the light-sensitive retina, causing distorted vision. Keratoconus can occur in one or both eyes.
Keratoconus Symptoms and Signs
Keratoconus can be difficult to detect, because it comes on slowly. Nearsightedness and astigmatism also accompany this disease, so you may have distorted and blurred vision. You might also notice glare and light sensitivity. Keratoconic patients often have prescription changes each time they visit their eyecare 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?
Causes of keratoconus are unclear. A genetic link may exist, as you may find several keratoconics within an extended family.
In the mildest form of keratoconus, eyeglasses or soft contact lenses may help. But as the disease progresses and the cornea thins and changes shape even more, glasses or soft contacts will no longer correct your vision.
Rigid gas permeable contact lenses are the next correction method of choice. The firmer material of a rigid contact lens holds the cornea in place better than a soft contact lens. Fitting contact lenses on a keratoconic cornea is delicate and time-consuming. You can expect frequent return visits to fine-tune the fit and the prescription. The process will begin again when the cornea thins and distorts even more, altering the contact lens fit and prescription needed for clear, comfortable vision.
A new treatment for keratoconus is corneal inserts. Intacs corneal rings received FDA approval in August 2004 to be marketed to correct or reduce nearsightedness and astigmatism in keratoconus patients who can no longer obtain functional vision with contact lenses or eyeglasses. The procedure involves placing the plastic inserts just under the surface of the eye in the periphery of the cornea. The result is a flatter cornea and clearer vision.
Several small studies have found that Intacs improved keratoconic participants’ eyeglass-corrected vision by an average of two lines on a standard eye chart. Other advantages are that the inserts are removable and exchangeable, the procedure takes only about 10 minutes, and while the inserts may defer a corneal transplant, they don’t preclude the procedure if necessary later on (see below). Potential risks are infection, little or no improvement in vision, glare and halos, and foreign body sensation, so it is important to discuss the procedure in detail with a surgeon to make sure you are a good candidate.
Intacs are also approved in the U.S. to correct nearsightedness in people with healthy eyes.
Some people with keratoconus can’t tolerate a rigid contact lens, or they reach the point where contact lenses or corneal inserts no longer provide acceptable vision. The next step may be a cornea transplant, also called a penetrating keratoplasty. Even after a transplant, you most likely will need glasses or contact lenses for clear vision.