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People usually develop a corneal ulcer after some type of corneal trauma, which allows bacteria, viruses, fungi, or parasites to enter the cornea. This invasion causes an infection with inflammation, which worsens if left untreated.
The types of infections that can lead to a corneal ulcer include:
Bacterial: People who wear contact lenses are at a higher risk for developing corneal ulcers, especially if they leave extended-wear lenses in their eyes for many days or weeks.
Viral: Corneal ulcers can be caused by the herpes simplex virus (causes cold sores).
Fungal: Improper hygiene of contact lenses or use of steroid eye drops can lead to fungal infections. They can also result from an injury to the cornea that lets plant material get into the eye, or from a suppressed immune system.
Parasitic: Acanthamoeba, microscopic, single-celled amoeba, are the most common amoeba in fresh water and soil. This parasite can cause severe eye infection, especially in contact lens wearers, which can lead to a corneal ulcer.
Other causes of corneal ulcers include:
Bell's palsy and other eyelid disorders that prevent the eyelid from closing all the way