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What Is the Cornea?

The cornea is the transparent tissue that covers the front of the eye. It helps provide a physical barrier that shields the inside of the eye from germs, dust, and other harmful matter, and acts as the eye’s outermost lens.

When light strikes the cornea, it bends – or refracts – the incoming light onto the crystalline lens, which then focuses the light onto the retina, the paper-thin tissue at the back of the eye that starts the translation of light into vision.

Although much thinner than the lens, the cornea provides about 65 percent of the eye's power to bend light. Most of this power resides in the center of the cornea, which is rounder and thinner than the outer part of the tissue and is thus better suited to bend lightwaves.

The cornea is essential to good vision.

What problems commonly affect the cornea?

The cornea copes very well with minor injuries or abrasions. If dirt scratches the highly sensitive cornea, epithelial cells slide over quickly and patch the injury before infection occurs and vision is affected.

But if the scratch penetrates the cornea more deeply, the healing process will take longer, resulting in greater pain, blurred vision, tearing, redness, and extreme sensitivity to light. These symptoms require professional treatment. Some of the more serious problems that affect the cornea are:

Microbial Infections (keratitis)

When the cornea is damaged, such as after a foreign object has penetrated the tissue, bacteria or fungi can pass into the cornea, causing a deep infection and inflammation. This condition may cause severe pain, reduce visual clarity, produce a corneal discharge, and perhaps erode the cornea.

As a general rule, the deeper the corneal infection, the more severe the symptoms and complications.

Conjunctivitis ("pink eye")

This term describes a group of inflammatory and often contagious diseases of the conjunctiva (the protective membrane that lines the eyelids and covers exposed areas of the sclera, or white of the eye). These diseases can be caused by a bacterial or viral infection, drug allergy, environmental irritants, or a contact lens product.

At its onset, pink eye is usually painless and does not adversely affect vision. The infection will come and go in most cases without requiring medical care. But for some forms of pink eye, such as epidemic keratoconjunctivitis, treatment will be needed. If treatment is delayed, the infection may worsen and cause corneal inflammation and a loss of vision.

Ocular Herpes

Although ocular herpes can result from the sexually transmitted herpes simplex II virus, it is usually caused by herpes simplex virus I (HSV I), the virus responsible for cold sores. In about 12 percent of those with ocular herpes, both eyes are involved.

Ocular herpes produces a relatively painful sore on the surface of the cornea. Prompt treatment with a anti-viral drug will help to stop the herpes virus from multiplying and destroying epithelial cells.

Like other herpetic infections, herpes of the eye remains a controllable, but incurable, problem.

Herpes Zoster (shingles)

This infection is produced by the varicella-zoster virus, the same virus that causes chicken pox. After an initial outbreak of chicken pox (often during childhood), the virus remains dormant within the nerve cells of the central nervous system. But in some people, the varicella-zoster virus will reactivate at some time during their lives. When this occurs, the virus travels down long nerve fibers and infects some part of the body, producing a blistering rash (shingles), fever, painful inflammations of the affected nerve fibers, and a general feeling of malaise.

Varicella-zoster virus may travel to the head and neck, perhaps involving an eye, part of the nose, mouth, cheek, and forehead. In about 40 percent of those with shingles in this area, the virus infects the cornea. These zoster-related corneal lesions will usually clear up on their own. But without early anti-viral treatment, a person runs the risk of the virus infecting cells deep within the tissue, causing inflammation and scarring of the cornea. The disease may also cause decreased corneal sensitivity. For many, this decreased sensitivity will be permanent.

Be aware that corneal complications may arise months after the shingles are gone. For this reason, it is important that patients schedule follow-up eye examinations.

Corneal Dystrophies

There are over 20 corneal dystrophies that affect all parts of the cornea.

What Are Cornea Transplants?

Corneal transplant surgery is performed to replace the clear surface on the front of the eye (the cornea).

Corneal transplantation is recommended for persons who have:

  • Thinning of the cornea that causes vision problems (keratoconus)
  • Scarring of the cornea from severe infections or injuries
  • Cloudiness of the cornea that causes vision loss (Fuchs dystrophy)

Who Are Mid-Florida Eye’s Cornea Specialists?

If you are interested in learning more about our treatments for corneal disorders, schedule an appointment with Mid Florida Eye Center serving the people of Mt. Dora, Leesburg, Adjacent to The Villages in Wildwood and Stonecrest.