The Cornea

The cornea is the eye’s outermost layer. It is the clear, dome­shaped surface that covers the front of the eye. It plays an important role in focusing your vision.

What are the parts of the cornea?

Although the cornea may look clear and seem to lack substance, it is a highly organized tissue. Unlike most tissues in the body, the cornea contains no blood vessels to nourish or protect it against infection. Instead, the cornea receives its nourishment from tears and the aqueous humor (a fluid in the front part of the eye that lies behind the cornea).

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Why are tears so important to the cornea?

Every time we blink, tears are distributed across the cornea to keep the eye moist, help wounds heal, and protect against infection. Tears form in three layers:

  • An outer, oily (lipid) layer that keeps tears from evaporating too quickly and helps tears remain on the eye;
  • A middle (aqueous) layer that nourishes the cornea and the conjunctiva – the mucous membrane that covers the front of the eye and the inside of the eyelids;
  • A bottom (mucin) layer that helps spread the aqueous layer across the eye to ensure that the eye remains wet
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What are some common conditions that affect the cornea?

Injuries

After minor injuries or scratches, the cornea usually heals on its own. Deeper injuries can cause corneal scarring, resulting in a haze on the cornea that impairs vision. If you have a deep injury, or a corneal disease or disorder, you could experience:

  • Pain in the eye
  • Sensitivity to light
  • Reduced vision or blurry vision
  • Redness or inflammation in the eye
  • Headache, nausea, fatigue

If you experience any of these symptoms, seek help from an eye care professional.

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What are corneal dystrophies?

A corneal dystrophy is a condition in which one or more parts of the cornea lose their normal clarity due to a buildup of material that clouds the cornea. These diseases:

  • Are usually inherited
  • Affect both eyes
  • Progress gradually
  • Don’t affect other parts of the body, and aren’t related to diseases affecting other parts of the eye or body
  • Happen in otherwise healthy people.

Corneal dystrophies affect vision in different ways. Some cause severe visual impairment, while a few cause no vision problems and are only discovered during a routine eye exam. Other dystrophies may cause repeated episodes of pain without leading to permanent vision loss. Some of the most common corneal dystrophies include keratoconus, Fuchs’ dystrophy, lattice dystrophy, and map­-dot­-fingerprint dystrophy.

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What other diseases can affect the cornea?

Herpes Zoster (Shingles)

Shingles is a reactivation of the varicel-la­zoster virus, the same virus that causes chickenpox. If you have had chickenpox, the virus can live on within your nerve cells for years after the sores have gone away. In some people, the varicel-la­zoster virus reactivates later in life, travels through the nerve fibers, and emerges in the cornea. If this happens, your eye care professional may prescribe oral anti­-viral treatment to reduce the risk of inflammation and scarring in the cornea. Shingles can also cause decreased sensitivity in the cornea.

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What treatments are there for advanced corneal disease?

Laser Surgery

Phototherapeutic keratectomy (PTK) is a surgical technique that uses UV light and laser technology to reshape and restore the cornea. PTK has been used to treat recurrent erosions and corneal dystrophies, such as map-dot-fingerprint dystrophy and basal membrane dystrophy. PTK helps delay or postpone corneal grafting or replacement.

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What research is being done?

Improved corneal wound healing could have an impact on many disorders and injuries of the cornea. NEI researchers are conducting studies to better understand how the cornea naturally heals after injury, which involves the release of proteins that act together to move the epithelial layer over the wound. This research could lead to new therapeutic strategies for transplantation and other treatments to repair corneal damage.

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Last Reviewed: May 2016

Courtesy: The National Eye Institute (NEI) is part of the National Institutes of Health (NIH) and is the Federal government’s lead agency for vision research that leads to sight-saving treatments and plays a key role in reducing visual impairment and blindness.

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