Infections of 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. It should be noted that microbial infections, although relatively infrequent, are the most serious complication of contact lens wear.

Minor corneal infections are commonly treated with anti-bacterial or anti-fungal eye drops. If the problem is more severe, a person may receive more intensive antibiotic treatment to eliminate the infection and may need to take steroid eye drops to reduce inflammation. Frequent visits to an eye care professional may be necessary for several months to eliminate the problem.

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. Depending on the type of pink eye that a person develops, treatment often consists of antibiotics and steroids.

Ocular Herpes

Herpes of the eye is a recurrent viral infection that affects an estimated 400,000 Americans with 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 anti-viral drugs helps to stop the herpes virus from multiplying and destroying epithelial cells. In time, the infection may also spread into the stroma, causing the body's immune system to attack and destroy stromal cells. This more severe infection, called herpes simplex stromal keratitis, is harder to treat and can scar the cornea, causing vision loss. It may also produce an infection of the inside of the eye.

Like other herpetic infections, herpes of the eye remains a controllable, but incurable, problem. For those who lose vision to ocular herpes, it usually results from recurrent attacks that lead to severe stromal keratitis. Studies indicate that after a person has had an initial outbreak of ocular herpes, he or she has better than a 50 percent chance of having a recurrence of the disease. This second outbreak could come weeks or decades after the initial attack. In one large study, researchers found that recurrence rates were 10 percent after one year, 23 percent at two years, and 63 percent at 20 years. Some factors associated with recurrence include fever, stress, sunlight, and trauma. Anyone with ocular herpes should avoid using over-the-counter steroid eye drops. Steroids cause the virus to multiply and the infection to worsen.

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.

Although shingles can occur in anyone exposed to the varicella-zoster virus, several studies have established two general risk factors for the disease: (1) advanced age and (2) a weakened immune system. Studies show that people over age 80 have a five times greater chance of having shingles than adults between the ages of 20 and 40. Unlike herpes simplex I, the varicella-zoster virus does not usually flare up more than once in adults with normally functioning immune systems.

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

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.