CHAPTER 224

Corneal Disorders

The cornea is the domed, transparent covering in the front of the eye that protects the iris and lens and helps focus light on the retina. It is composed of cells, protein, and fluid. The cornea looks fragile but is almost as stiff as a fingernail. However, it is very sensitive to touch.

Corneal disease or damage can cause pain, tearing, and loss of vision. A slit lamp, which shows the cornea with magnification, is usually used to examine the cornea (see page 1423). A doctor may apply eye drops that contain a dye called fluorescein, which temporarily stains areas of the cornea where cells are damaged, making these areas easier to identify.

Superficial Punctate Keratitis

Superficial punctate keratitis is death of small groups of cells on the surface of the cornea.

The eyes become red, watery, and sensitive to light.

Most people recover fully.

Symptoms can be relieved.

The cause of this disorder may be any of the following:

A viral infection

A bacterial infection (including trachoma—see page 1439)

Dry eyes

Strong chemicals splashed in the eye

Exposure to ultraviolet light (sunlight, sunlamps, or welding arcs)

Prolonged use of contact lenses

An allergy to eye drops

Blepharitis (eyelid inflammation)

A side effect of certain drugs taken by mouth or vein (intravenously)

In superficial punctate keratitis, the eyes are usually painful, watery, sensitive to bright light, and bloodshot, and vision may be slightly blurred. Often there is a burning, gritty feeling or a feeling as if a foreign object is trapped in the eye. When ultraviolet light causes the disorder, symptoms usually do not occur until several hours after exposure and last for 1 to 2 days. When a virus causes the disorder, a lymph node in front of the ear on the affected side may be swollen and tender.

The diagnosis is based on the symptoms, on whether the person has been exposed to any of the known causes, and on an examination of the cornea with a slit lamp (a device used by a doctor to examine the eye with magnification—see page 1423).

Almost everyone who has this disorder recovers completely. When the cause is a virus (other than herpes simplex or herpes zoster [shingles]), no treatment is needed, and recovery usually occurs within 3 weeks. When the cause is a bacterial infection or prolonged use of contact lenses, antibiotics are used, and the wearing of contact lenses is temporarily discontinued. When the cause is dry eyes, ointments and artificial tears are effective. Artificial tears are eye drops prepared with substances that simulate real tears or with substances that when added to the person’s tears coat the eye with more moisture. When the cause is exposure to ultraviolet light, an antibiotic ointment and an eye drop that dilates the pupil may provide relief. When the cause is a drug reaction or an allergy to eye drops, the drug or eye drops must be discontinued.

Corneal Ulcer

A corneal ulcer is an infected open sore on the cornea.

Contact lenses, injuries, disorders, drugs, and nutritional deficiencies can cause open sores.

Pain, foreign body sensation, redness, tearing, and light sensitivity are common.

Antibiotic, antiviral, or antifungal drugs are usually given as soon as possible.

Corneal ulcers may begin with a corneal injury, which then becomes infected with bacteria, fungi, or the protozoan Acanthamoeba (which lives in contaminated water). Viral ulcers (often due to a herpes virus) can be triggered to recur by physical stress or may recur spontaneously. Ulcers can also occur if a foreign object lodges in the eye or, more often, if the eye is irritated by a contact lens, especially when contact lenses are worn during sleep or are not adequately disinfected. A deficiency of vitamin A and protein may lead to the formation of a corneal ulcer. However, such ulcers are rare in the United States.

When the eyelids do not close properly, the cornea may become dry and irritated. This kind of irritation can lead to injury and the development of a corneal ulcer. Corneal ulcers may also result from in-growing eyelashes (trichiasis), an inturned eyelid (entropion), or eyelid inflammation (blepharitis).

Symptoms

Corneal ulcers cause pain, usually a feeling like a foreign object is in the eye, with aching and sensitivity to bright light and increased tear production. The ulcer often appears as a white spot on the cornea. Sometimes, ulcers develop over the entire cornea and may penetrate deeply. Pus may accumulate behind the cornea, sometimes forming a white layer at the bottom of the cornea. The deeper the ulcer, the more severe the symptoms and complications. The conjunctiva usually is bloodshot, and a mucus-like white discharge is present.

Corneal ulcers may heal with treatment, but they may leave a cloudy scar that impairs vision. Other complications may include deep-seated infection, perforation of the cornea, displacement of the iris, and destruction of most or all of the tissue in the eye socket.

Diagnosis

To see an ulcer clearly, a doctor may apply eye drops that contain a dye called fluorescein, which temporarily stains the ulcer and allows it to be examined more clearly.

Treatment

A corneal ulcer is an emergency that should be treated immediately.

Treatment depends on the underlying cause. For instance, antibiotic, antiviral, or antifungal drugs are usually needed immediately. Corneal transplantation (keratoplasty) is sometimes needed (see box on page 1135).

Keratoconjunctivitis Sicca

Keratoconjunctivitis sicca (dry eye) is dryness of the conjunctiva and cornea.

Too few tears may be produced, or tears may evaporate too quickly.

The eyes become irritated and sensitive to light and usually burn and itch.

Tear production may be measured by placing a strip of paper at the edge of the eyelid.

Artificial tears help relieve symptoms.

Dry eyes may be due to inadequate tear production (aqueous tear-deficient dry eyes). With this type of dry eyes, the tear gland (lacrimal gland) does not produce enough tears to keep the entire conjunctiva and cornea covered by a complete layer of tears. This is the most common type among postmenopausal women. Dry eyes are common in Sjögren’s syndrome (see page 577). Rarely, aqueous tear-deficient dry eyes may be a symptom of diseases such as rheumatoid arthritis or systemic lupus erythematosus (lupus).

Dry eyes may also be due to an abnormality of tear composition that results in rapid evaporation of the tears (evaporative dry eyes). Although the tear gland produces a sufficient amount of tears, the rate of evaporation is so rapid that the entire surface of the eye cannot be kept covered with a complete layer of tears during certain activities or in certain environments.

Symptoms

Symptoms of dry eyes include irritation, burning, itching, a pulling sensation, pressure behind the eye, and a feeling as if something is in the eye. Damage to the surface of the eye increases discomfort and sensitivity to bright light. Symptoms are worsened by

Activities in which the rate of blinking is reduced, specifically those that involve prolonged use of the eyes, such as reading, working on a computer, driving, or watching television

Drafty, dusty or smoky areas and dry environments, such as in airplanes or in shopping malls; areas with low humidity; and areas where air conditioners (especially in the car), fans, or heaters are being used

The use of certain drugs, including isotretinoin and some tranquilizers, diuretics, antihypertensives, oral contraceptives, and antihistamines and other drugs with anticholinergic effects

Symptoms lessen during cool, rainy, or foggy weather and in humid places, such as in the shower.

Even with the most severe dry eyes, it is rare that vision is lost. However, people sometimes feel that their blurred vision or eye irritation is so severe, frequent, and prolonged that it is difficult to function normally. In some people with severe dryness, the surface of the cornea can thicken, or ulcers and scars can develop. Occasionally, blood vessels can grow across the cornea. Scarring and blood vessel growth can impair vision.

Diagnosis

Although a doctor can usually diagnose dry eyes by the symptoms alone, a Schirmer test—in which a strip of filter paper is placed at the edge of the eyelid—can measure the amount of moisture bathing the eye. Doctors examine the eyes with a slit lamp (see page 1423) to determine whether the eye has been damaged.

Treatment

Artificial tears applied every few hours can generally control the problem. Artificial tears are eye drops prepared with substances that simulate real tears and help keep the eyes coated with moisture. Lubricating ointments applied before bed last longer than artificial tears and help prevent dryness in the morning. Such ointments are not usually used during the day because they may blur vision.

Eye drops that contain cyclosporine can decrease the inflammation associated with dryness. These drops sting and take months before an effect is noticed. Inflammation can lessen significantly, although the drops work only in a small number of people. Avoiding dry, drafty environments and smoke and using humidifiers can also help.

Minor surgery can be done to block the flow of tears through the tear duct into the nose. This way more tears are available to bathe the eyes. In people with extremely dry eyes, the eyelids may be partially sewn together to decrease tear evaporation.

Keratomalacia

Keratomalacia (also called xerophthalmia or xerotic keratitis) is drying and clouding of the cornea due to vitamin A deficiency and insufficient protein and calories in the diet.

The surface of the conjunctiva and cornea dries, sometimes leading to corneal ulcers and bacterial infections. The tear glands are also affected, resulting in an inadequate tear film and dry eyes. Night blindness (poor vision in the dark) may develop because of the effects of vitamin A deficiency on the retina. The diagnosis of keratomalacia is based on the presence of a dry or ulcerated cornea in an undernourished person.

Antibiotic eye drops or ointments can help cure an infection, but correcting the vitamin A deficiency and undernutrition with an improved diet or supplements is also important.

Herpes Simplex Keratitis

Herpes simplex keratitis is infection of the cornea caused by herpes simplex virus.

The herpes simplex virus (which causes cold sores—see page 1245) never leaves the body after an initial infection (primary infection). Instead, the virus remains in a dormant stage in the nerves. Sometimes, the virus reactivates and causes further symptoms.

Primary herpes simplex eye infections usually occur in children and cause a mild keratoconjunctivitis. Symptoms usually resemble those of common conjunctivitis, so the diagnosis of herpes simplex infection is not made. The infection resolves without treatment. However, if the infection reactivates, it can affect the cornea more seriously and cause more severe symptoms.

Symptoms of a reactivation include eye pain, tearing, redness, and sensitivity to bright light. Rarely, the infection worsens and the cornea swells, making vision hazy. The more often the infection recurs, the more likely is further damage to the surface of the cornea. Several recurrences may result in the formation of deep ulcers, permanent scarring, and a loss of feeling when the eye is touched. The herpes simplex virus can also cause blood vessels to grow onto the cornea and, occasionally, can lead to significant visual impairment. To diagnose a herpes simplex infection, a doctor examines the eye with a slit lamp (see page 1423). Sometimes, the doctor may take a sample from the infected area to identify the virus (viral culture).

The doctor may prescribe an antiviral eye drop, such as trifluridine. Acyclovir, another antiviral drug, can be taken by mouth. Treatment should be started as soon as possible. Deep infections that cause a lot of inflammation may require use of corticosteroid drops and drops that dilate the eye, such as atropine or scopolamine. Occasionally, to help speed healing, after numbing the eye, an ophthalmologist (a medical doctor who specializes in diagnosing and treating eye diseases and performing eye surgery) may have to gently swab the cornea with a soft cotton-tipped applicator to remove infected and damaged cells.

Herpes Zoster Ophthalmicus

Herpes zoster ophthalmicus is infection of the eye caused by varicella-zoster virus.

Varicella-zoster is the virus that causes chicken pox. Once people are infected, the virus remains in a dormant stage in the nerve roots. In some people, the virus reactivates and may spread to the skin, causing herpes zoster, also called shingles (see page 1247). If the forehead or nose becomes infected, the eye also becomes infected in about half of people, on the same side as the skin involvement.

The skin of the forehead and sometimes the tip of the nose are covered with small, extremely painful, red blisters. Infection of the eye causes pain, redness, light sensitivity, and eyelid swelling. Months and years later, the cornea can become swollen, severely damaged, and scarred. The structures behind the cornea can become inflamed (uveitis), the pressure in the eye can increase (glaucoma), and the cornea can become numb, which can lead to injuries. The appearance of active shingles, a history of the typical rash, or old scars from a shingles rash help a doctor make the diagnosis.

As with shingles anywhere in the body, early treatment with an antiviral drug such as acyclovir, valacyclovir, or famciclovir (which are taken by mouth) can reduce the duration of the painful rash. When herpes zoster infects the face and threatens the eye, treatment with an antiviral drug reduces the risk of eye complications. Corticosteroids, usually in eye drops, may also be needed if the eye is inflamed. Eye drops, such as atropine, are used to keep the pupil dilated, to help prevent a severe form of glaucoma, and to relieve pain.

Peripheral Ulcerative Keratitis

Peripheral ulcerative keratitis is inflammation and ulceration of the cornea that often occurs in people who have connective tissue disorders such as rheumatoid arthritis.

Peripheral ulcerative keratitis is probably caused by an autoimmune reaction (see page 1124). People develop blurred vision, increased sensitivity to bright light, and a sensation of a foreign object trapped in the eye. The ulcer is located in the periphery of the cornea and is usually oval in shape.

Of the people who have rheumatoid arthritis and peripheral ulcerative keratitis, about 40% die (mostly due to a heart attack) within 10 years of developing peripheral ulcerative keratitis unless they are treated. Treatment with drugs that suppress the immune system, such as oral or intravenous cyclophosphamide, reduces the death rate to about 8% in 10 years.

Keratoconus

Keratoconus is a gradual change in the shape of the cornea that causes it to become irregular and cone-shaped.

The condition usually begins between the ages of 10 and 25. Both eyes are usually affected, causing major changes in vision and requiring frequent changes in the prescription for eyeglasses or contact lenses. Contact lenses often correct the vision problems better than eyeglasses, but sometimes the change in corneal shape is so severe that contact lenses either cannot be worn or cannot correct vision. In severe cases, corneal transplantation (see box on page 1135) may be needed to restore vision. Some newer alternatives to transplantation, such as insertion of corneal ring segments (objects that change the shape of the cornea to help correct refraction) or ultraviolet light treatments that strengthen the cornea, may become more available in coming years.

Bullous Keratopathy

Bullous keratopathy is a blister-like swelling of the cornea.

Bullous keratopathy is most common among older people. Occasionally, bullous keratopathy occurs after eye surgery, such as cataract removal. The swelling leads to the formation of fluid-filled blisters on the surface of the cornea. The blisters can rupture, causing pain, often with the sensation of a foreign object trapped in the eye, and can impair vision.

The diagnosis is based on the typical appearance of a swollen, cloudy cornea with blisters on the surface.

Bullous keratopathy is treated by reducing the amount of fluid in the cornea. Salty eye drops (hypertonic saline) can be used to draw the excess fluid from the cornea. Soft contact lenses can be used to decrease discomfort by acting as a bandage to the cornea. If vision is reduced or discomfort is significant and prolonged, corneal transplantation (see box on page 1135) is often done.