Eye Health: Keratoconus

We see through the cornea, which is the clear, central part of the front surface of the eye. Normally, the cornea has a dome shape, like a ball. Sometimes, however, the structure of the cornea is just not strong enough to hold this round shape and the cornea bulges outward like a cone. This condition is called keratoconus.

What Causes Keratoconus?

Often the cause of keratoconus is unknown. Some studies have found that keratoconus runs in families, and that it happens more often in people with certain medical problems, including certain allergic conditions. Some think that chronic eye rubbing can cause keratoconus. But most often, there is no eye injury or disease that could explain why the eye starts to change.

Keratoconus usually begins in the teenage years, but it can also start in childhood or up to about age 30. The changes in the shape of the cornea occur slowly, usually over several years.

Someone with keratoconus will notice that vision slowly becomes distorted. The change can stop at any time, or it can continue for several years. In most people who have keratoconus, both eyes are eventually affected, although not always to the same extent.

Can Keratoconus Damage Vision?

Keratoconus does not make people go blind. However, the changes to the cornea can make it impossible for the eye to focus without eyeglasses or contact lenses.

Keratoconus can be dangerous if laser vision correction surgery -- LASIK or PRK is performed on the eye.

Anyone with even a small amount of keratoconus should not have laser vision correction surgery.

How Is Keratoconus Diagnosed?

The doctor may notice some things during the examination, or the patient may mention symptoms, that could be caused by keratoconus. These include:

• Sudden change of vision in just one eye.
• Double vision when looking with just one eye.
• Objects both near and far look distorted, but not blurred. In other words, small details of the objects are clear, but the shapes or colors look wrong. Later, distant objects do become blurred.
• Bright lights look like they have halos around them.

These things might be related to keratoconus, but your doctor must measure the curvature of the cornea to be certain. Several different instruments can be used to measure the curvature of the cornea.

One instrument, called a keratometer, shines a pattern of light onto the cornea. The shape of the reflection of the pattern tells the doctor how the eye is curved. There are also computerized instruments that make three-dimensional "maps" of the cornea, a process called corneal topography.