Q: My neighbor's son developed cone-eye. What is this disease, and why did he have to go to Canada to be treated?

Q: My neighbor's son developed cone-eye. What is this disease, and why did he have to go to Canada to be treated?

A: The cornea is the dome-shaped clear covering in the front of the eye. Keratoconus (which is what I think you mean by cone-eye) is a condition that causes the cornea to weaken and thin, eventually bulging from its round shape to become cone-shaped. It may also lead to scarring, possibly exacerbated by irritation from eye rubbing.

The exact cause of keratoconus is unknown, but proteases -- which are enzymes that break down proteins -- are thought to affect the cross-linkages of the connective tissues of the cornea of patients with this condition. Environmental (possibly linked to allergies) and/or genetic factors may also play a role.

Keratoconus usually begins to manifest in patients in their late teens or 20s, although it can occur at any age. It affects as many as one in every 500 to 2,000 Americans, although there is a genetic linkage (at least in some cases) so the incidence is higher in those with a family history of keratoconus. The severity of this condition varies quite a bit from one patient to another.

Keratoconus is usually a slowly progressive disease over 10 to 20 years which may then stabilize, but in some patients it may progress rapidly. It is usually bilateral, although it often affects one eye more than the other.

The abnormal thickness and shape of the cornea, as well as the scarring, affects the vision of patients with keratoconus. The earliest symptom is usually blurry vision that cannot be completely corrected with glasses (although in most patients vision can be restored with gas-permeable contact lenses, at least initially). Keratoconus may also distort the patient's vision, possibly causing multiple or streaky images. It may affect the patient's ability to drive, read and/or perform other routine tasks. Vision is often most impaired at night. Keratoconus also causes photophobia (abnormal sensitivity to light) in some patients.

Keratoconus is first suspected based on the patient's symptoms. It may be diagnosed based on a thorough eye exam, including the use of a slit lamp (which is, basically, a special light source and a binocular magnifier to better view the details of the eye). Very specialized tests, called corneal topography (to map the shape of the cornea) and pachymetry (to measure the thickness of the cornea) may be used in some cases to verify the diagnosis.

Early in the course of keratoconus, glasses may help improve vision but they do not treat the underlying corneal weakness or shape change. Contact lenses may help vision and address some of the early corneal distortion. There are also tiny plastic braces that may be placed surgically to improve the corneal shape.

If the cornea is too thin or distorted for any of these treatments, a corneal transplant (where the center of the cornea is replaced by a donor cornea form a cadaver) may be recommended.

There is fairly new treatment for keratoconus that was pioneered in Germany called corneal collagen crosslinking with riboflavin. In this treatment a one-time application of riboflavin eye drops (a B vitamin) is activated with low-dose ultraviolet light for about half an hour to cause a reaction that produces extra cross-linking bonds. This treatment actually addresses the underlying cause of keratoconus by strengthening the cornea. This procedure is already approved in Europe and Canada, and is now in clinical trials in the United States. Since this treatment is only in the clinical trial stage in the U.S., it is only available at a limited number of clinical trial sites and only under the study protocol. When the trial is completed the results will be evaluated and the FDA will make a determination of whether this procedure is sufficiently safe and efficacious to be approved for more widespread use in the U.S.

People who have rapidly changing eyeglass prescriptions or who have vision changes that cannot be adequately corrected with glasses, as well as close family members of patients diagnosed with keratoconus, should be screened for keratoconus. Patients diagnosed with this condition should see an experienced ophthalmologist and should discuss what treatment is best for them. They will need to be closely monitored for any changes in their condition and for any further treatment recommendations.

Jeff Hersh, Ph.D., M.D., F.A.A.P., F.A.C.P., F.A.A.E.P., can be reached at DrHersh@juno.com.