Corneal ulcers are usually caused by the following types of infections:
- Bacterial infections
These are common in contact lens wearers, especially in people using extended-wear lenses. Acanthamoeba keratitis is particularly common in contact lens users, especially those who make their own homemade cleaning solutions.
- Viral infections
The virus that causes cold sores (the herpes simplex virus) may cause recurring attacks that are triggered by stress, an impaired immune system, or exposure to sunlight. Also, the virus that causes chicken pox and shingles (the varicella virus) can cause corneal ulcers.
- Fungal infections
Improper use of contact lenses or steroid eyedrops can lead to fungal infections, which in turn can cause corneal ulcers. Also, a corneal injury that results in plant material getting into the eye can lead to fungal keratitis.
- Parasitic (Acanthamoeba) infections
Acanthamoeba are microscopic, single-celled amoeba that can cause human infection. They are the most common amoebae in fresh water and soil. When Acanthamoeba enters the eye it can cause severe infection, particularly for contact lens users.
Other causes of corneal ulcers include:
- Abrasions or burns to the cornea caused by injury to the eye. Scratches, scrapes and cuts from fingernails, paper cuts, makeup brushes and tree branches can become infected by bacteria and lead to corneal ulcers. Burns caused by caustic chemicals found in the workplace and at home can cause corneal ulcers.
- Dry eye syndrome.
- Bell's palsy and other eyelid disorders that prevent proper eyelid function. If the eyelid does not function properly, the cornea can dry out.
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