Most horse owners have discovered their horse with an eye problem at some point in time. Common symptoms include: thick discharge, swollen lids, squinting, tearing, or just excessively red eyes. So what could be causing the problem and how serious is the situation? Almost any abnormality with a horse’s eye should be treated like an emergency. It may not need to be examined immediately, but realistically should be seen the same day as the problem is noted. Some of these symptoms could be caused by something as simple as dust in the eyes or allergies, but could also be indicative of a more serious condition.
One of the most common eye abnormalities that veterinarians treat are corneal scratches or “ulcers”. The cornea is the top layer of cells on the surface of the eye itself. Normal cornea is several millimeters thick and is clear. Signs of a corneal scratch may include excessive squinting or tearing in the effected eye. In later stages, if there is infection present, there may be blue, green, or white discoloration of the cornea and the ocular discharge may be white or yellow. Horses with corneal scratches also seem to be very sensitive to sunlight and may spend more time in the shade avoiding the sun. Even a small scratch in a horse eye is extremely susceptible to secondary infection from bacteria or fungus. Once an infection is present, depending on the organism involved, the cornea may become thinner at the site of the scratch (“melting ulcer”) and the eye can actually rupture if bacteria penetrate deeply enough. For this reason, any scratch on the cornea should be treated aggressively and quickly to reduce the chance of infection. Once an infection is present in the cornea, it can be difficult to treat and in some cases, the horse may even have to be hospitalized for care. In rare instances, the infection cannot be controlled and the eye may need to be removed.
Another more harmless condition is a clogged tear duct. Horses have a small channel called a nasolacrimal canal that runs from the inside corner of their eye and drains out a small hole inside the nostril. When tears are produced, they drain down the nasolacrimal canal and into the nose. It is normal for horses to have a small amount of clear fluid draining from their nose as it is actually tears draining from their eyes. When an excess of dirt or mucus plugs the nasolacrimal canal, then tears do not drain appropriately and you will see excessive tearing or discharge on the horse’s face near the eye. This can appear in one or both eyes. Horses with allergies seem more prone to clogging of the nasolacrimal canals. Although not an emergency, it can be hard to distinguish a clogged tear duct from a corneal scratch without a detailed eye exam, so if you notice a lot of drainage from the eye, please call your vet right away. Your veterinarian will likely feed a small plastic tube into the lower opening of the tear duct inside the nostril. He or she will then gently flush saline through the tear duct to try to dislodge anything impeding drainage.
Another serious eye condition in horses is called “uveitis” or “moonblindness”. In this condition, there is inflammation within the eye. The exact reason why horses develop uveitis is not always known, but there has been implication of various bacteria and parasites that may incite inflammation as they migrate through the eye. Direct trauma to the eye can also induce uveitis. There is some genetic predisposition, with appaloosa horses being at much higher risk for uveitis than any other breed. Horses with uveitis tend to be very sensitive to light and may seek shade, or have their eye squinted shut and watering more than usual. Uveitis can affect one or both eyes. In severe cases, you may notice a blue or white discoloration of the cornea. This is caused by fluid leaking into the cornea and causing swelling of the corneal tissue secondary to inflammation. Uveitis can be very serious and in many cases it will continue to recur throughout a horse’s life. Each flare up increases the risks of developing glaucoma, cataracts, and eventually blindness in the eye
A final thought regarding your horse’s eyes is that you should never place ANY ointment into the eye without having a veterinary exam performed first. The type of ointment used to treat uveitis could have potentially disastrous consequences if applied to a corneal scratch. So if you suspect a problem with the eye, it is always safest to have your veterinarian examine the eye first.
If you have any questions feel free to contact me,
Dr Shannon Harland