A.ombination of the above may be necessary early in the disease course. Corneal ulcers are more common in contact lens wearers, possibly due to the rubbing of a dirty or defective  lens against the surface of the eye. The horse's eye is especially vulnerable to trauma due to its prominent position, compared with other species. A corneal ulcer is very painful. Medline . St. Besides bacterial infection, other causes of corneal ulcers are fungi and parasites, such as: Fusarium. Most complications from corneal ulcers occur because the ulcer has been left untreated. A corneal ulcer is an open sore

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