What is Keratoconus?
Keratoconus is a non-inflammatory eye condition in which the shape of the cornea becomes distorted. The cornea is a clear structure that covers the front of the eye and allows light to enter the eye. In a healthy eye, the cornea curves like a dome. In an eye with keratoconus, the center of the cornea slowly thins and bulges, so that it sags and has a cone shap.
In rare cases of keratoconus, the posterior layer of the cornea may tear becasue of the stretching forces within it. When this happens, the cornea may suddenly become swollen with water (termed hydrops). 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.
How common is keratoconus?
Keratoconus occurs in 50 to 230 per 100,000 population.
Who gets keratoconus?
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 has been found in all races and in both sexes but affects women more often than men. It occurs more frequently in patients with Down’s syndrome, allergies, asthma or certain rare congenital eye diseases
What are the symptoms of keratoconus?
The symptoms of keratoconus usually start in puberty (in the teens) and may progress for the next 10 to 20 years. The early symptoms of keratoconus include:
- decreased vision
- worsening nearsightedness
Blurring and distortion of vision are common early symptoms. Rarely, keratoconus is first diagnosed when sudden swelling (hydrops) develops. This occurs most often in patients with Down’s syndrome.
How is keratoconus diagnosed?
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. This occurs most often in patients with Down’s syndrome. Keratoconus has been found in all races and in both sexes but affects women more often than men. It occurs more frequently in patients with Down’s syndrome, allergies, asthma or certain rare congenital eye diseases.
How is keratoconus treated?
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. Usually these lenses are 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. Swelling (hydrops) in a keratoconus cornea may require treatment with eye drops. 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. (The whole eye cannot be transplanted, only the cornea.) 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. Keratoconus usually is discovered when a patient sees an optometrist or ophthalmologist because of decreased vision.
How does one decide when to have a corneal transplant?
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 the patient with contact lenses, especially if there is not significant corneal scarring affecting vision.
Can keratoconus lead to blindness?
With the proper treatment (glasses, contact lenses, or a corneal transplant), most people with keratoconus will enjoy good vision for the rest of their lives. Thanks to modern contact lenses and surgical techniques, it is rare for someone with keratoconus to be severely visually disabled.
