Keratoconus

Keratoconus is when the cornea of the eye becomes thin and develops a cone-like bulge. The misshapen cornea brings light rays into the eye out of focus, distorting your vision and making everyday tasks challenging.

On this page

• What Is Keratoconus?
• What Are the Symptoms of Keratoconus?
• How Do You Diagnose Keratoconus?
• How Do You Treat Keratoconus?

What Is Keratoconus?  

Doctors define keratoconus as a condition in which the cornea becomes thin and develops a cone-like bulge.

The cornea is the clear, dome-shaped outer layer of the eye that focuses light into the eye. A misshapen cornea prevents light rays entering the eye from focusing properly on the retina. This distorts your vision and can make performing everyday tasks difficult.

What causes keratoconus? 

The cause of keratoconus is unknown, but it has a genetic component. Roughly 1 in 10 people with keratoconus has a close family relative with it, too.

What are keratoconus risk factors and complications?  

Keratoconus risk factors  

 Risk factors for keratoconus include having:

• A connective tissue disorder, such as Ehler-Danlos or Marfan syndrome.
• A history of asthma, allergies, or retinitis pigmentosa.
• An eye allergy.
• A habit of frequent eye rubbing, especially aggressive knuckling-type eye rubbing.
• Other health conditions, such as Down syndrome, Leber congenital amaurosis, and mitral valve prolapse.

Complications of keratoconus  

Some people never know they have keratoconus because symptoms develop slowly over many years. But in a small number of people, keratoconus worsens quickly.

Sometimes, tiny cracks form in the cornea from the strain of the bulging cone, causing rapid swelling and a sudden and pronounced decrease in vision. The swelling may last for weeks or months, and vision may grow even more distorted and blurry. When these cracks heal over time, they produce scar tissue, and the cornea loses its smooth surface and becomes milky.  

If you have sudden swelling, your doctor can prescribe eyedrops for temporary relief.

How common is keratoconus?

According to the National Institutes of Health (NIH), keratoconus is rare, affecting roughly 1 in every 2,000 Americans.

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What Are the Signs and Symptoms of Keratoconus?

Keratoconus often starts in your teens or early 20s. In its earliest stages, keratoconus may cause slight blurring, visual distortion, and heightened sensitivity to light. As it progresses over 10 to 20 years, the cornea bulges more, and vision may become more distorted.

Both eyes are often affected by keratoconus, but symptoms can differ in each eye and change over time.

Early-stage keratoconus symptoms may include:

• Blurred vision.
• Distorted vision.
• Increased light and glare sensitivity.
• Red or swollen eyes.
• Eye redness or swelling.

Late-stage keratoconus symptoms include:

• Blurrier and even more distorted vision.
• Changing eyeglasses prescriptions.
• Inability to wear contact lenses due to discomfort or poor fit.  
• Increased nearsightedness (inability to see at a distance).
• Increased astigmatism (inability to focus).

When should I see a doctor about my keratoconus symptoms?

When symptoms of keratoconus — such as blurriness, distortion of vision, or sensitivity to light or glare — bother you or interfere with your activities of daily living, make an appointment to see your eye doctor.

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How Do You Diagnose Keratoconus? 

An ophthalmologist can diagnose keratoconus through a regular eye exam and a measurement of your corneal curves. Your doctor may use a special computer to create a corneal map showing the cornea’s surface condition, which they'll use to monitor changes over time.

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How Do You Treat Keratoconus? 

Treatment for keratoconus depends on your symptoms. Early-stage keratoconus may require only eyeglasses or soft contact lenses to treat mild symptoms of vision impairment.

Later-stage keratoconus symptoms may be treated with:

• Corneal cross-linking (CXL) — A procedure that uses UV light and eyedrops to flatten the cornea, halting or slowing bulging progression.
• Corneal transplant — A surgery in which all or part of your damaged cornea is replaced with healthy donor tissue.
• Hard contact lenses — Special lenses to keep your vision focused.
• Intacs — Small, curved devices implanted in the cornea to flatten the curvature and improve vision.

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By UPMC Editorial Staff. Last reviewed on 2025-07-15.