Keratoconus is a deteriorating condition of the eye in which the normally round, dome-shaped cornea (clear front surface of the eye) becomes increasingly thinner in some areas. This causes a cone-like bulge to develop in the area where the cornea is thinnest- usually in the center. This results in blurred vision and frequent changes in the strength of glasses/contacts. The exact cause of keratoconus is unknown. It occurs in about 1 out of every 2,000 people in the general population. It is found in all parts of the world but is more common in certain geographic and ethnic populations, such as Asians. Keratoconus is usually first diagnosed in young people at puberty or in the late teens. It is usually bilateral (occurring in both eyes), but the symptoms may be quite different between the two eyes. It most often occurs randomly, but it can be inherited. It typically progresses over a 10-20-year period and then gradually stops.
Fig. 1: Keratoconus
What causes keratoconus?
The exact cause of keratoconus is unknown and is likely multi-factorial. This means there is a combination of multiple factors- environmental, behavioral, and genetic which contribute to the disease. Eye rubbing is a major behavioral factor in the disease. Whether the eye rubbing causes the disease or is a sign of other factors occurring in keratoconus is unknown. Changes in multiple genes have been associated with keratoconus. Children with an affected first degree relative are much more likely to develop keratoconus. Malfunctioning enzymes that normally help maintain the health of the cornea may play a role. All of these factors contribute to the main problem in keratoconus, which is the defective collagen structure that results in thinning and irregularity of the cornea. Keratoconus occurs more frequently in patients with atopy (asthma and eczema) or severe ocular allergies as well as patients with Down Syndrome, Marfan’s syndrome, and Leber’s congenital amaurosis.
What are the symptoms of keratoconus?
The changes in the cornea which occur in keratoconus result in rapid changes in the focusing needs of the eye, most commonly worsening of nearsightedness (difficulty seeing far away) and irregular astigmatism (loss of the normal curvature of the eye). In early keratoconus, patients typically notice blurring of their vision, often worse at night. They may also have photophobia (sensitivity to light). Patients often complain of multiple “ghost images” as well as streaking and distortion around lights. The condition is usually painless, although pain and redness can occur if a corneal blister (hydrops) develops. Scarring of the cornea from hydrops can cause uncorrectable decreased vision.
How is keratoconus diagnosed?
Keratoconus is diagnosed by a careful eye examination by an ophthalmologist. Vision will be measured, and a slit lamp and dilated examination will be performed. Corneal topography which creates a digital, three-dimensional map of the corneal surface helps to confirm the diagnosis.
How is keratoconus treated?
Mild cases of keratoconus may be treated with glasses or soft contact lenses, but most cases require rigid gas permeable (hard) contact lenses to provide the best vision.
When hard contact lenses are not sufficient, or are not tolerated by the patient, other procedures may be considered. Intracorneal ring segments (Intacs) can be surgically implanted to reduce the cornea’s cone shape. There is also growing support for the use of collagen crosslinking with riboflavin and UVA light (CXL) to fortify the structure of the cornea. This treatment causes new bonds to form across collagen bands, and results in increased corneal strength and improvement of the cone-like shape. Careful follow up care is required after treatment to ensure there is no further worsening, as children often have more aggressive disease than in adults.
About 10-25% of patients may experience decreased vision and scarring severe enough to warrant a corneal transplant procedure.
LASIK is not recommended for patients with keratoconus, because this type of operation can accelerate thinning of the cornea.
Where can I learn more about keratoconus?