August 28, 2009

Horses are blessed with large, lovely eyes that are very prominent on their faces. Unfortunately, these characteristics make it easy for horses to injure their eyes.

"Corneal ulcers are the most common eye problem in horses," said Dr Nicki Wise, of Washington State University.

"Ulcers are usually due to a traumatic injury. Something as simple as scratching their eye on a tree branch or getting a piece of hay in their eye can cause an ulcer. Often times, owners have no idea what the horse injured themselves on." The cornea is the thin, clear, outer layer of the eye.

Several cell layers make up the cornea, which is only about two millimeters thick. Injuries that only affect the first layer, called the epithelium, are considered abrasions and are the easiest to treat. Injuries that penetrate into the second layer, called the stroma, are considered ulcers and can cause considerable damage if left untreated.

Signs that a horse has an injured eye include squinting, excessive tearing, swelling around the eyelids and mucous membranes, and possibly pus-like discharge.

"Owners will likely see their horse squinting or holding an eye shut, and the eye may be watery and sensitive to light," Dr Wise said.

"If you notice this, call a veterinarian to examine the horse. He or she can find out if there is an ulcer and how deep it is, which determines what medication is used.

"Most corneal ulcers are easy to deal with and don't require major diagnostics or treatment," she said.

"But if an ulcer is left untreated, it can quickly become infected with bacteria or fungi, which will make the problem more severe and may result in the loss of the eye or blindness within days."

Horses with eye injuries may not want their head to be touched. To perform an examination, a veterinarian usually sedates the horse or blocks the injured eye with a local anesthetic. Often a fluorescent stain is used to determine how deep the injury penetrated into the cornea.

"If the ulcer is not deep, it can be treated with a topical antibiotic ointment. It can take a variable amount of time to heal, from days to weeks," Dr Wise said.

"It is very important that owners not use antibiotics out of their own medicine cabinet because if steroids are in those ointments, that could make the ulcer much, much worse."

Horses with corneal ulcers will likely be sensitive to light, so it is best to use a fly mask or keep them in a darkened stall until the eye is healed.

"The prognosis for most horses that receive treatment is good, unless the eye perforates or a melting ulcer occurs," Dr Wise said.

Melting ulcers can occur from certain bacteria that produce enzymes that destroy the stroma. These ulcers can become large, form quickly, and usually have a jelly-like or melting appearance. If left untreated, the eyeball may rupture, resulting in blindness.

"For more serious cases, we have surgical procedures for stabilizing the eye and treating the infection by placing an indwelling catheter into the eye to provide continuous medication," she said.

This is especially useful for horses with conditions that take weeks to heal and do not like having their eye medicated.