Keratoconus is an eye disorder in which your cornea thins over time. The cornea also bulges out to form a conelike shape.

The cornea is the outer layer of the eye. It's a clear layer that covers the front of your eye. It helps protect your eye from germs and debris. It also helps focus light into your eye. With keratoconus, your cornea thins in the lower and center parts. This condition can also cause swelling and scarring of your cornea. These changes to the cornea can cause vision problems, such as nearsightedness (myopia) and astigmatism.

There are different types of keratoconus based on the shape and location of the thinned cornea. These types include nipple, oval, keratoglobus, and D-shaped keratoconus.

Keratoconus is not a common condition. It happens more often in young adults in their teens and twenties. It affects both sexes equally.

Experts don't know what causes keratoconus. Some cases may be partly due to genes.

Some health conditions are linked to this disorder and may help to cause it. They include:

• Down syndrome
• Ehlers-Danlos syndrome
• Eye injury (especially from too much eye rubbing or contact lens use)
• Leber congenital amaurosis
• Osteogenesis imperfecta
• Retinitis pigmentosa
• Retinopathy of prematurity
• Vernal keratoconjunctivitis
• Sleep apnea

Certain factors may increase your risk:

• A history of poorly fitted contact lenses
• Long-term (chronic) eye rubbing due to eye irritation, such as from allergies
• Having a health condition linked to keratoconus

Keratoconus causes nearsightedness (myopia). This means you have trouble seeing objects that are far away. It also causes astigmatism. This is a problem with your eye creating a focused image on your retina. Together, these lead to blurry vision.

Keratoconus often causes symptoms in both eyes. One eye may have symptoms before the other. One eye may be affected more than the other eye.

Symptoms often start during puberty and get worse until about age 40. You may not know you have this disorder unless your eye doctor does special tests. Later, your vision may get much worse. Your doctor may evaluate you for keratoconus if your vision is getting worse than expected.

Your eye doctor will ask about your health history and give you an eye exam. They will test the sharpness of your vision. You may need to have your eyes dilated for part of the exam. For this, your doctor will give you eye drops that widen (dilate) the dark part in the center of your eye (pupil). This lets your doctor see the back part of your eye more clearly. Your doctor may also use a device to measure the curvature of your cornea.

The early stages of keratoconus may not be found unless your eye doctor is looking for signs of the disease. An imaging test called corneal topography may help your doctor make the diagnosis. This test shows changes in the shape of the cornea.

Your treatment may vary according to the severity of your keratoconus. Your treatment choices may also vary according to your specific type of keratoconus.

Early on, you may only need to wear glasses to correct the visual defect from your keratoconus. Special contact lenses are another choice if glasses don't work. Often these are gas-permeable contacts. These require careful fitting to your cornea.

Many people won't need any other treatment. But if your cornea gets too scarred or can't handle a contact lens, you may need another kind of treatment. The traditional treatment in this situation is a corneal transplant. This surgery removes part or all of the original corneal thickness. It's replaced with the cornea from a donor who has died (cadaver donor).

More recently, eye doctors have developed other surgery choices to treat keratoconus. They both can help improve your vision. They include:

• Artificial rings placed inside your cornea (corneal ring segments)
• Artificial lenses placed inside your eye
• Stiffening the cornea by placing eye drops containing riboflavin on the cornea, then shining an ultraviolet light on the cornea (corneal collagen cross-linking)

Sometimes eye doctors will use a mix of treatments for better results. Each of these procedures has its own risks and benefits. Ask your doctor about what treatment or treatments make sense for you.

In rare cases, severe keratoconus causes a complication called corneal hydrops. This happens when part of your cornea breaks. This causes the fluid in your eye to flow into your cornea abnormally. This can cause severe pain and swelling. It may also cause sudden vision loss.

You may need to wear special contact lenses or use special eye drops if you have corneal hydrops. Often this condition goes away in a few weeks.

Most cases are not preventable. You may be able to reduce your chance of getting keratoconus by:

• Protecting your eyes from UV radiation with sunglasses
• Making sure your contact lenses fit well
• Getting treatment for any kind of eye discomfort (for example, from allergies)
• Not rubbing your eyes

Contact your eye doctor right away if you have sudden vision loss or sudden pain in your eye.

• Keratoconus is a disorder in which your cornea thins and becomes abnormally shaped over time.
• It causes nearsightedness and astigmatism. It may make your vision blurry.
• Experts don't know exactly what causes it. Some health problems may make it more likely.
• In its early stages, glasses or contacts may be the only treatment you need.
• Some people will need other procedures, such as corneal transplant surgery.
• Advanced keratoconus sometimes causes corneal hydrops. This may cause sudden vision loss.

Tips to help you get the most from a visit to your doctor:

• Know the reason for your visit and what you want to happen.
• Before your visit, write down questions you want answered.
• Bring someone with you to help you ask questions and remember what your doctor tells you.
• At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new instructions your doctor gives you.
• Know why a new medicine or treatment is prescribed, and how it will help you. Also know what the side effects are.
• Ask if your condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if you do not take the medicine or have the test or procedure.
• If you have a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your doctor if you have questions. This includes after hours and on weekends and holidays.