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Corneal Ulcer (cont.)

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What are the causes of a corneal ulcer?

Most corneal ulcers are caused by infections. Bacterial infections cause corneal ulcers and are common in contact lens wearers. Bacteria can directly invade the cornea if the corneal surface has been disrupted. Some bacteria produce toxins that can cause ulceration of the cornea. This is seen in peripheral ulcerative keratitis due to the staphylococcal bacteria. Viruses that may cause corneal ulcers include the herpes simplex virus (the virus that causes cold sores) and the Varicella virus (the virus that causes both chickenpox and shingles) if it involves the upper eyelid and tip of nose (herpes zoster ophthalmicus). Although these viral illnesses usually cause only herpes simplex or herpes zoster keratitis, corneal ulcers can develop. Fungal infections can cause corneal ulcers and may occur with improper care of contact lenses or overuse of eyedrops that contain steroids. Parasites like Acanthamoeba may also cause corneal ulcers.

Tiny cuts or scratches in the corneal surface may become infected and lead to corneal ulcers. For example, metal, wood, glass, or almost any type of particle that strikes the cornea can cause minor trauma. Such injuries damage the corneal surface and make it easier for bacteria to invade and cause a corneal ulcer. A corneal abrasion is a larger loss of the corneal surface and may ulcerate if left untreated.

Disorders that cause dry eyes (keratitis sicca) can leave the eye without the germ-fighting protection of the tear film and cause or aggravate corneal ulcers.

Disorders that affect the eyelid and prevent the eye from closing completely, such as Bell's palsy, can dry the cornea and make it more vulnerable to ulcers. In addition, mechanical problems of the lid turning inward toward the eye or lashes growing inward and rubbing against the cornea can cause corneal ulcers.

Any condition which causes loss of sensation of the corneal surface may increase the risk of corneal ulceration.

Chemical burns or other caustic (damaging) solutions splashing into the eye can injure the cornea and lead to corneal ulceration.

People who wear contact lenses are at an increased risk of corneal ulcers. The risk of corneal ulcers and other complications are lowest with daily wear disposable lenses. The risk of corneal ulceration increases at least tenfold when using extended-wear lenses. Extended-wear contact lenses are those contact lenses that are worn for several days without removing them at night.

Scratches on the edge of the contact lens can scrape the cornea's surface and make it more open to bacterial infections. Similarly, tiny particles of dirt trapped underneath the contact lens can scratch the cornea. Bacteria may be on the improperly cleaned contact lens and get trapped on the undersurface of the lens. If lenses are left in eyes for long periods of time, bacteria can multiply and cause damage to the cornea. Wearing contact lenses for extended periods of time can also block oxygen to the cornea, making it more susceptible to infections. Improper care of contact lenses also increases the risk of corneal ulcer.

In addition, some patients with immunological disorders (immunosuppressed, rheumatoid arthritis, lupus, and others) may develop corneal ulcers as a complication of their disease. Patients with immune-mediated scleritis can also develop corneal ulcers.

Mooren's corneal ulcer is a painful, recurrent, usually unilateral ulcerative keratitis that begins peripherally and progresses circumferentially and sometimes centrally. It is likely due to an eye-specific immune mechanism. It can frequently lead to corneal thinning and perforation, which must be treated surgically. Patients with Mooren's ulcer should be evaluated for a generalized autoimmune disorder.

Medically Reviewed by a Doctor on 9/14/2017

Source: MedicineNet.com
https://www.medicinenet.com/corneal_ulcer/article.htm

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