Cornea

What is the cornea?

The cornea is the clear window on the front of your eye. It’s made of tough, transparent tissue.

Together with the sclera (white of your eye), the cornea helps protect your eye. It keeps out dirt, germs and other particles. The cornea also filters out some of the sun’s ultraviolet (UV) light.

How does the cornea help you see?

The cornea plays a key role in vision. Its main job is to help your eyes focus. The cornea has a slight curvature. As light enters your eye, the shape of the cornea refracts (bends) it. The curve helps your eye focus on objects that are close or far away.

What are the layers of the cornea?

The cornea has five layers:

• Epithelium: The epithelium is the outer layer of the cornea. It stops any material from entering the eye. It absorbs oxygen and nutrients from tears.
• Bowman’s layer: This thin layer connects the epithelium and the stroma, the next layer.
• Stroma: The thickest layer of the cornea is behind the epithelium. It’s made up of water and protein. The stroma is elastic (stretchy) but solid. The stroma gives the cornea its domed shape.
• Descemet’s membrane: This thin layer separates the stroma from the endothelium.
• Endothelium: This single layer of cells is between the stroma and the aqueous humor. The aqueous humor is the clear fluid in the front of your eye. The endothelium works as a pump that removes extra water that the stroma can’t absorb.

What are common corneal disorders?

Disease, infection or injury may damage your cornea. If that happens, scars or discoloration can form. This damage can block or distort light as it enters your eye. Your cornea can also become cloudy, and your vision may blur.

Cornea problems include:

• Dry eye: Some people’s eyes don’t produce enough tears. Dry eye can cause discomfort and vision problems when the cornea is affected.
• Keratitis: Keratitis can result from an infection or inflammation. Contact lenses are the most common cause of keratitis.
• Scratches: Small corneal abrasions (scratches) or other corneal injuries typically heal by themselves. A deeper cornea scratch or eye injury can lead to scars or problems with your eyesight if you don’t get treatment.
• Corneal dystrophies: More than 20 diseases fall under corneal dystrophies. These conditions include keratoconus and Fuchs’ dystrophy. They can cause structural problems with the cornea. You experience cloudy vision the layers of the cornea are irregular or because material builds up on the cornea.
• Uncommon cornea problems: There are many other corneal diseases, including ocular herpes, a viral eye infection.

What treatments are available for corneal conditions?

Healthcare providers can treat most corneal conditions with prescription eye drops or oral medications (drugs you take by mouth). For keratoconus, specialized contact lenses may help.

If you have advanced corneal disease, you may need:

• Laser treatment: A laser treatment called phototherapeutic keratectomy (PTK) which can reshape the cornea.
• Corneal transplant: You may need a corneal transplant if your cornea has severe damage. You get a new cornea from a donor.
• Artificial cornea: As an alternative to a corneal transplant, your provider uses an artificial cornea to replace a damaged cornea.

How can I prevent injury to my corneas?

You can take steps to keep your cornea healthy. Wear goggles or safety glasses when you:

• Do home repairs such as painting, hammering or using a drill.
• Mow the lawn, use a string trimmer or do other yardwork that may produce flying grass and dirt.
• Play games that use a puck, like hockey, or a ball, like baseball, tennis or racquetball.
• Use machines or chemicals.

How can I keep my corneas healthy?

To keep your corneas healthy:

• Keep contact lenses clean: If you wear contact lenses, follow the directions to keep them clean. You need to clean and disinfect them regularly. Store them correctly and replace them as your healthcare provider directs.
• Get regular eye exams: Eye specialists can check for cornea conditions as part of an eye exam. Your eye care provider may use special eye drops that make corneal scratches easier to see.
• Wear sunglasses: Although your cornea keeps out some of the sun's UV rays, it’s safest for your eye health to wear sunglasses when you’re outside.

What should I do if something is stuck in my eye?

If you feel like something is stuck in your eye:

• Blink a few times to try and dislodge it.
• Pull your upper eyelid over your lower lid to create tears to wash your eye.
• Rinse your eye with saline or clean water.

Don’t:

• Rub your eye, which may scratch the cornea.
• Try to remove an object from your eye. Go to your eye doctor or the nearest emergency room.

When should I call my healthcare provider about corneal problems?

Go to your eye doctor or the nearest emergency room if you experience:

• Any object stuck in your eyes.
• Blurry vision or vision changes.
• Eye trauma, such as getting hit in the eye.
• Intense eye pain.
• Very red, watery eyes.

A note from Cleveland Clinic

The cornea is the clear outer layer of your eye. It helps your eyes focus and keeps germs and particles out of your eye. Wear sunglasses when you’re outside. Protect your corneas by wearing goggles or safety glasses when dust or other particles could fly into your eye. If you wear contact lenses, clean and disinfect them regularly. And make sure to have regular eye exams. An eye professional can check for scratches on your cornea or other problems.