What is keratoconus?

We see through the cornea, which is the clear, central part of the front surface of the eye. The cornea normally has a round shape, like a ball.

Sometimes, however, the structure of the cornea is not strong enough to hold this round shape. Over time, the normal round curvature of the surface of the eye can bulge outward like a cone. This condition is called keratoconus.

Keratoconus usually begins in the teenage years, but it can also start in childhood or up to about age 30. In some cases, keratoconus is diagnosed at a later age, but usually only because it is very mild. The changes in the shape of the cornea occur slowly, usually over several years.

Keratoconus changes vision in two ways:

  • As the cornea changes from a ball shape to a cone shape, the smooth surface also warps. This change is called irregular astigmatism, which cannot be fully corrected with glasses.
  • As the front of the cornea steepens, the eye becomes more nearsighted (poor vision at distance; only nearby objects can be seen clearly). As a result, the person may need new eyeglasses more often.

What are the symptoms of keratoconus?

The main symptoms of keratoconus are the following:

  • The vision in one or both eyes gradually gets worse, usually in late adolescence.
  • The person has double vision when looking with just one eye, even with glasses on.
  • Bright lights look like they have halos around them.

Someone with keratoconus will notice that his or her vision slowly becomes distorted. The change can end at any time, or it can continue for several years. In most people who have keratoconus, both eyes are eventually affected.

Why do people get keratoconus?

The cause of keratoconus is largely unknown. Some studies have found that keratoconus runs in families, and that it happens more often in people who have certain medical conditions. But in most cases, there is no eye injury or disease that explains why the eye starts to change. Patients with keratoconus tend to rub their eyes a lot, which may cause the condition to develop more rapidly.