What is keratoconus?
Keratoconus is a slowly progressive eye condition that affects the clear, front surface of the eye - the cornea. The normally round, dome-shaped cornea weakens and thins, causing a cone-like bulge to develop. The regular curvature of the cornea becomes irregular, resulting in increasing nearsightedness (myopia) and astigmatism that have to be corrected with special glasses or contact lenses. Since the cornea is responsible for refracting (bending and focusing) most of the light coming into the eye, corneal abnormalities can result in significant visual impairment, making simple tasks like driving or watching TV difficult.
Keratoconus is estimated to occur in one out of every 2,000 persons in the general population. Generally, it is first diagnosed in young people at puberty or in their late teens. There is no known significant geographic, cultural or social pattern.
What causes keratoconus?
The cause of keratoconus is unknown. Studies indicate that keratoconus stems from one of several possible causes:
an inherited corneal abnormality; about seven percent of those with the condition have a family history of keratoconus or high astigmatism;
an eye injury such as excessive eye rubbing or wearing hard contact lenses for many years;
certain eye diseases, such as retinitis pigmentosa, retinopathy of prematurity, and vernal keratoconjunctivitis;
systemic diseases, such as Leber's congenital amaurosis, Ehlers-Danlos syndrome, Down syndrome and osteogenesis imperfecta;
with atopic dermatitis and psoriasis in adolescents.
Keratoconus usually affects both eyes, although one eye is usually more severely affected. The progression of the condition is generally slow and can stop at any stage from mild to severe. In its earliest stages, keratoconus causes slight blurring and distortion of vision and increased sensitivity to glare and light. Glasses and contact lens prescriptions may change frequently. As the condition advances, vision decreases even with the best possible glasses or contacts. Thinning and scarring of the cornea worsens in the advanced stages.
Occasionally, a person may experience a sudden loss of vision in one eye that clears over a period of weeks or months. This is due to fluid leaking into the cornea through small breaks in one of the thinned layers and is called corneal hydrops.
Initial treatment for acute corneal hydrops is conservative. Eye drops are used to draw excess fluid out of the cornea. However, it may be necessary to perform a penetrating keratoplasty (corneal graft) if the cornea is in danger of rupturing.
In most cases, eyeglasses or soft contact lenses are used to correct the mild nearsightedness and astigmatism that is caused in the early stages of keratoconus. As the disorder progresses and the cornea continues to thin and change shape, rigid, gas permeable contact lenses are prescribed to correct vision more adequately. The contact lenses must be custom fitted. Frequent checkups to observe the status of the cornea and to monitor changes in the corrective lenses are needed to achieve and maintain good vision.
Intacs, thin plastic rings that are surgically inserted into the cornea in order to flatten and change its abnormal shape, have recently received FDA approval for treatment of keratoconus. They can improve vision and decrease the need for strong glasses and contact lenses. However, they do not necessarily slow or stop the progression of the disease, but are designed to stabilize the cornea.
Sometimes, a corneal transplant may be needed due to scarring, extreme thinning or contact lens intolerance. This surgical procedure replaces the keratoconus cornea with healthy donor corneal tissue that is sutured in place.