Overview

Keratoconus (ker-uh-toe-KOH-nus) occurs when your cornea — the clear, dome-shaped front surface of your eye — thins and gradually bulges outward into a cone shape.

A cone-shaped cornea causes blurred vision and may cause sensitivity to light and glare. Keratoconus usually affects both eyes and generally begins to first affect people ages 10 to 25. The condition may progress slowly for 10 years or longer.

In the early stages of keratoconus, you can correct vision problems with glasses or soft contact lenses. Later you may have to be fitted with rigid gas permeable contact lenses or other types of lenses. If your condition progresses to an advanced stage, you may need a cornea transplant.

Keratoconus care at Mayo Clinic

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Symptoms

Signs and symptoms of keratoconus may change as the disease progresses. They include:

• Blurred or distorted vision
• Increased sensitivity to bright light and glare, which can cause problems with night driving
• A need for frequent changes in eyeglass prescriptions
• Sudden worsening or clouding of vision

When to see a doctor

See your eye doctor (ophthalmologist or optometrist) if your eyesight is worsening rapidly, which might be caused by an irregular curvature of the eye (astigmatism). He or she may also look for signs of keratoconus during routine eye exams.

If you're considering laser-assisted in-situ keratomileusis (LASIK) eye surgery, your doctor will check for signs of keratoconus before you proceed.

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Causes

No one knows what causes keratoconus.

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Diagnosis

To diagnose keratoconus, your eye doctor (ophthalmologist) will review your medical and family history and conduct an eye exam. He or she may conduct other tests to determine more details regarding the shape of your cornea. Tests to diagnose keratoconus include:

• Eye refraction. In this test your eye doctor uses special equipment that measures your eyes to check for vision problems. He or she may ask you to look through a device that contains wheels of different lenses (phoropter) to help judge which combination gives you the sharpest vision. Some doctors may use a hand-held instrument (retinoscope) to evaluate your eyes.

• Slit-lamp examination. In this test your doctor directs a vertical beam of light on the surface of your eye and uses a low-powered microscope to view your eye. He or she evaluates the shape of your cornea and looks for other potential problems in your eye.

  The doctor may repeat the test after you've had eyedrops applied to dilate your pupils. This helps with viewing the back of your eye.

• Keratometry. In this test your eye doctor focuses a circle of light on your cornea and measures the reflection to determine the basic shape of your cornea.
• Computerized corneal mapping. Special photographic tests, such as optical coherence tomography and corneal topography, record images of your cornea to create a detailed shape map of your cornea's surface. The tests can also measure the thickness of your cornea.

Source: http://www.mayoclinic.com

Complications

In some situations, your cornea may swell quickly and cause sudden reduced vision and scarring of the cornea. This is caused by a condition in which the inside lining of your cornea breaks down, allowing fluid to enter the cornea (hydrops).

In advanced keratoconus, your cornea may become scarred, particularly where the cone forms. A scarred cornea causes worsening vision problems and may require corneal transplant surgery.

Risk factors

These factors can increase your chances of developing keratoconus:

• Having a family history of keratoconus
• Rubbing your eyes vigorously
• Having certain conditions, such as retinitis pigmentosa, Down syndrome, Ehlers-Danlos syndrome, hay fever and asthma

Source: http://www.mayoclinic.com