Keratitis is an inflammation of the cornea, the transparent membrane that covers the colored part of the eye (iris) and pupil of the eye.
There are many types and causes of keratitis. Keratitis occurs in both children and adults. Organisms cannot generally invade an intact, healthy cornea. However, certain conditions can allow an infection to occur. For example, a scratch can leave the cornea open to infection. A very dry eye can also decrease the cornea's protective mechanisms.
Risk factors that increase the likelihood of developing this condition include:
- poor contact lens care; overuse of contact lenses
- illnesses or other factors that reduces the body's ability to overcome infection
- cold sores, genital herpes, and other viral infections
- crowded, dirty living conditions; poor hygiene
- poor nutrition (especially a deficiency of Vitamin A, which is essential for normal vision)
Some common types of keratitis are listed below, however there are many other forms.
Herpes simplex keratitis
- chronic inflammation of the cornea
- development of tiny blood vessels in the eye
- loss of vision
This infection generally begins with inflammation of the membrane lining the eyelid (conjunctiva) and the portion of the eyeball that comes into contact with it. It usually occurs in one eye. Subsequent infections are characterized by a pattern of lesions that resemble the veins of a leaf. These infections are called dendritic keratitis and aid in the diagnosis.
Recurrences may be brought on by stress, fatigue, or ultraviolet light (UV) exposure (e.g., skiing or boating increase the exposure of the eye to sunlight; the sunlight reflects off of the surfaces). Repeated episodes of dendritic keratitis can cause sores, permanent scarring, and numbness of the cornea.
Recurrent dendritic keratitis is often followed by disciform keratitis. This condition is characterized by clouding and deep, disc-shaped swelling of the cornea and by inflammation of the iris.
It is very important not to use topical corticosteroids with herpes simplex keratitis as it can make it much worse, possibly leading to blindness.
People who have bacterial keratitis wake up with their eyelids stuck together. There can be pain, sensitivity to light, redness, tearing, and a decrease in vision. This condition, which is usually aggressive, can be caused by wearing soft contact lenses overnight. One study found that overnight wear can increase risk by 10-15 times more than if wearing daily wear contact lenses. Improper lens care is also a factor. Contaminated makeup can also contain bacteria.
Bacterial keratitis makes the cornea cloudy. It may also cause abscesses to develop in the stroma, which is located beneath the outer layer of the cornea.
Usually a consequence of injuring the cornea in a farm-like setting or in a place where plant material is present, fungal keratitis often develops slowly. This condition:
- usually affects people with weakened immune systems
- often results in infection within the eyeball
- may cause stromal abscesses
Peripheral ulcerative keratitis
Peripheral ulcerative keratitis is also called marginal keratolysis or peripheral rheumatoid ulceration. This condition is often associated with active or chronic:
- rheumatoid arthritis
- relapsing polychondritis (connective-tissue inflammation)
- wegener's granulomatosis, a rare condition characterized by kidney disease and development of nodules in the respiratory tract
Superficial punctate keratitis
Often associated with the type of viruses that cause upper respiratory infection (adenoviruses), superficial punctate keratitis is characterized by destruction of pinpoint areas in the outer layer of the cornea (epithelium). One or both eyes may be affected.
This pus-producing condition is very painful. It is a common source of infection in people who wear soft or rigid contact lenses. It can be found in tap water, soil, and swimming pools.
Photokeratitis or snowblindness is caused by excess exposure to UV light. This can occur with sunlight, suntanning lamps, or a welding arc. It is called snowblindness because the sunlight is reflected off of the snow. It therefore can occur in water sports as well, because of the reflection of light off of the water. It is very painful and may occur several hours after exposure. It may last one to two days.
Also called parenchymatous keratitis, interstitial keratitis is a chronic inflammation of tissue deep within the cornea. Interstitial keratitis is rare in the United States. Interstitial keratitis affects both eyes and usually occurs as a complication of congenital or acquired syphilis. In congenital syphilis it can occur between age two and puberty. It may also occur in people with tuberculosis, leprosy, or other diseases.
Causes and symptoms
In summary, keratitis can be caused by:
- bacterial, viral, or fungal infections
- dry eyes resulting from disorders of the eyelid or diminished ability to form tears
- exposure to very bright light
- foreign objects that injure or become lodged in the eye
- sensitivity or allergic reactions to eye makeup, dust, pollen, pollution, or other irritants
- vitamin A deficiency, which people with normal diets rarely develop
Symptoms of keratitis include, but are not limited to:
- sensitivity to light
- inflammation of the eyelid
- decrease in vision
A case history will be taken and the vision will be tested. Examination with a slit lamp, an instrument that's a microscope and focuses a beam of light on the eye, is important for diagnosis. The cornea can be examined with fluorescein, a yellow dye which will highlight defects in the cornea. Deeper layers of the cornea can also be examined with the slit lamp. Infiltrates, hazy looking areas in the cornea, can be seen by the doctor and will aid in the diagnosis. Samples of infectious matter removed from the eye will be sent for laboratory analysis.
Antibiotics, antifungals, and antiviral medication will be used to treat the appropriate organism. Broad spectrum antibiotics will be used immediately, but once the lab analysis determines the offending organism the medication may be changed. Sometimes more than one medication is necessary. It depends upon the infection, but the patient should be clear on how often and how to use the medications.
A sterile, cotton-tipped applicator may be used to gently remove infected tissue and allow the eye to heal more rapidly. Laser surgery is sometimes performed to destroy unhealthy cells, and some severe infections require corneal transplants.
Antifungal, antibiotic, or antiviral eyedrops or ointments are usually prescribed to cure keratitis, but they should be used only by patients under a doctor's care.
A patient with keratitis may wear a patch to protect the healing eye from bright light, foreign objects, the lid rubbing against the cornea, and other irritants. Sometimes a patch can make it worse, so again, the patient must discuss with the doctor whether or not a patch is necessary. The patient will probably return every day to the eye doctor to check on the progress.
Although early detection and treatment can cure most forms of keratitis, the infection can cause:
Children and adults who wear contact lenses should always use sterile lens-cleaning and disinfecting solutions. Tap water is not sterile and should not be used to clean contact lenses. It is important to go for follow-up checkups because small defects in the cornea can occur without the patient being aware of it. Do not overwear contact lenses. Remove them if the eyes become red or irritated. Replace contact lenses when scheduled to do so. Proteins and other matter can deposit on the contacts, leading to an increased risk of infection. Rinse contact lens cases in hot water every night, if possible, and let them air dry. Replace contact lens cases every three months. Organisms have been cultured from contact lens cases.
Eating a well-balanced diet and wearing protective glasses when working or playing in potentially dangerous situations can reduce anyone's risk of developing keratitis. Protective goggles can even be worn mowing the lawn so that if twigs are tossed up they can't hurt the eye. Goggles or sunglasses with UV coatings can help protect against damage from UV light.
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American Academy of Ophthalmology. 655 Beach Street, P.O. Box 7424, San Francisco, CA 94120-7424. <http://www.eyenet.org>.
American Optometric Association. 243 North Lindbergh Blvd., St. Louis, MO 63141. (314) 991-4100. <http://www.aoanet.org>.
National Eye Institute. 2020 Vision Place, Bethesda, MD 20892-3655. (301) 496-5248. <http://www.nei.nih.gov>.
Prevent Blindness America. 500 East Remington Road, Schaumburg, IL 60173. (800) 331-2020. <http://www.preventblindness.org>.
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Abscess—A collection of pus.
Infiltrate—A collection of cells not usually present in that area. In the cornea, infiltrates may be a collection of white blood cells.
Inflammation—A localized response to an injury. May include swelling, redness, and pain.