Keratoconus occurs in 50 to 230 per 100,000 population, and affects women more often than men. It occurs more frequently in patients with Down’s syndrome, allergies or asthma.
Symptoms of keratoconus usually start in puberty (in the teens) and may progress for the next 10 to 20 years. The early symptoms include decreased vision and worsening nearsightedness. Blurring and distortion of vision are common. Wrinkles and scars may also form on a keratoconus cornea.
People with keratoconus may suffer from decreased vision in two ways:
- From distortion of the cornea: Seeing through a misshapen cornea is like taking pictures with a camera whose lens has an irregular (not smooth) surface. Parts of the picture or field of vision are in focus and parts are out of focus. This visual problem is called irregular astigmatism.
- From scarring or swelling of the cornea: Seeing through a scarred or swollen cornea is like taking pictures with a camera with a dirty or cloudy lens. The picture or vision is blurred.
Despite a great deal of experience with keratoconus, the cause is still unknown. Some believe that keratoconus is developmental (genetic) in origin. It is known that 13% of patients have a relative with keratoconus. Others believe it is a degenerative condition. Keratoconus may also develop in persons who have worn contact lenses for a long time. An important factor identified in many keratoconus patients is that they often rub their eyes with too much force. This excessive eye rubbing may weaken the structural strength of the cornea, allowing bulging to occur or progress.
Keratoconus usually is discovered when a patient sees an ophthalmologist or optometrist because of decreased vision. The diagnosis of keratoconus can be made through careful examination of the eye. Sometimes, computerized mapping of the corneal shape (corneal topography) is necessary to confirm the diagnosis.
When diagnosed in the early stages, keratoconus may be corrected with eyeglasses, which may require frequent changes in the astigmatism prescription. As the disease advances, contact lenses usually are necessary to provide good vision, most often the hard or rigid gas permeable (RGP) type. Specialized designs of contact lenses are available and are constantly being improved, allowing for fitting of more advanced cases of keratoconus. If there is severe distortion or scarring of the cornea and contact lens wear is not possible or does not provide adequate vision, a corneal transplant is needed. This occurs in approximately 20% of patients. A corneal transplant replaces a diseased cornea with a normal cornea from a deceased donor. Most people who receive corneal transplants see very clearly after the surgery. Success rates of corneal transplantation in keratoconus are higher than 90%. While the surgical transplantation of a new cornea will resolve the basic problem of corneal shape irregularity, eyeglasses or contact lenses are usually needed for vision correction after surgery. Due to the irregular shape of the cornea following transplantation, soft contact lenses seldom provide satisfactory vision.
A corneal and contact lens specialist must decide when corneal transplantation is the best recommendation for a specific patient. This is often not a simple, straight-forward decision. Many factors must be considered and balanced, including the patient’s functional needs, the long recovery period (possibly up to one year) and the risk of complications. Very careful contact lens fittings are often attempted before recommending a corneal transplant. One study found that 69% of patients, most of whom were being referred for surgery, could be successfully fit with contact lenses using special designs. Therefore, prior to making the decision to proceed to surgery, every effort should be made to optimally fit a patient with contact lenses, especially if there is not significant corneal scarring affecting vision.
With the proper treatment (glasses, contact lenses or a corneal transplant), most people with keratoconus will enjoy good vision throughout their lives. With modern contact lenses and surgical techniques, it is rare for someone with keratoconus to be severely visually disabled.