Keratitis
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Definition
Keratitis is an inflammation of the cornea, the transparent membrane that covers the colored part of the eye (iris) and pupil of the eye.
Description
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 keratitisA major cause of adult eye disease, herpes simplex keratitis may lead to:
- chronic inflammation of the cornea
- development of tiny blood vessels in the eye
- scarring
- loss of vision
- glaucoma
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.
Bacterial keratitisPeople 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.
Fungal keratitisUsually 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 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
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.
Acanthamoeba keratitisThis 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.
PhotokeratitisPhotokeratitis 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.
Interstitial keratitisAlso 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.
— Maureen Haggerty
