Equine eye problems
Swollen eyelids
The most common cause for swollen eyelids is trauma in the form of blunt injury to the head, such as collision with solid objects. As long as the eye itself is undamaged and only the eyelids are affected, treatment is fairly straightforward. Non-steroidal anti-inflammatory drugs are very helpful. Banamine is better for ocular inflammation than Bute, but both are suitable. Topical application of ice is also helpful. Generally treatment results in rapid improvement.
There are other causes of eyelid swelling. Self-trauma can occur, for example horses suffering from severe colic will smack their heads against the ground when rolling violently. Insect bites can be another cause. Allergic reactions can cause swollen eyelids. With an allergic reaction, generally both eyelids swell, as do other head structures, such as the muzzle and nostrils. Allergic reactions that cause this sort of swelling require immediate veterinary attention.
More severe trauma can result in more serious damage involving the globe itself. For example, fracture of the bones of the orbit, hemorrhage into the anterior chamber, uveitis, dislocation of the lens, and retinal detachment.
Eyelid lacerations
Unfortunately eyelid lacerations are fairly common. Probably one of the main causes is normal scratching behavior. Horses love to scratch and the area around the eyes is a particularly difficult area to attend to, especially when you don’t have hands. Sharp metallic objects do a wonderful job, until one unfortunately hooks the eyelid. It is important to preserve the normal eyelid margin to ensure proper eyelid function. Consequently, eyelid lacerations need prompt veterinary attention. Swelling develops quickly and interferes with repair.
Nasolacrimal duct obstruction
Horses have a long tear duct that funnels old tear film out of the eye and down into the nostril. Obstruction of this duct results in an overflow of tears, which end up streaming down the face. Most commonly, obstruction is caused by debris and mucus. The duct can be flushed out while the horse is lightly sedated. In some cases, the blockage is permanent, such as damage to the skull, tumors, or scar tissue within the duct.
Corneal abrasions
Horses are by nature active and athletic. As previously mentioned, they also have a large, prominent eye. Consequently it is not so surprising that they commonly suffer injury to the eye, including abrasion to the cornea. Corneal scratches are extremely painful, unlike simple eyelid swelling. Tears often run down the face, because the pain causes overproduction of tears. Like wounds in other areas, damaged cornea develops edema. Corneal edema causes loss of transparency and cloudiness. The damaged cornea causes inflammation deeper into the eye, called uveitis. This results in a tightly closed, constricted pupil. Treatment consists of topical ophthalmic antibiotics to help defend against bacterial infection. Non-steroidal anti-inflammatory drugs such as Bute or Banamine are important to help ease the pain. Atropine is used to open the pupil and relax the muscles in the iris.
Equine Recurrent Uveitis (ERU)
This disease is more commonly known as Moon Blindness. There are other medical names also, such as Periodic Ophthalmia. It is one of the most common causes of blindness in horses. The overall incidence in the United States has been estimated at 8%. The disease is due to malfunctioning of the immune system and there are several types and stages to the disease. The classic form has recurrent bouts of severe uveitis with cloudiness in the cornea, cloudiness in the anterior chamber, severe pain, sensitivity to bright light, and a severely constricted pupil. Commonly there are quiet periods when the inflammation subsides but these periods are followed by increasingly severe episodes. Cloudy areas on the cornea become permanent, scar tissue develops inside the eye between the iris and lens, the corpora nigrans shrinks, and the iris can change color. The entire globe of the eye shrinks in size and cataracts often develop. Some develop glaucoma as a secondary problem.
There is a more insidious form of Moon Blindness, which is more common in Appaloosa and draft breeds. The inflammation is much more mild, chronic, with much less discomfort. It does however progress steadily and eventually also leads to blindness.
Treatment centers around two main goals – reducing inflammation, generally with corticosteroids, and reducing pain, primarily by getting the pupil to dilate with Atropine and using analgesic medications such as Banamine. Surgical procedures are showing promise at preventing the recurrence of uveitis. The recurring nature of the disease often leads to blindness and surgical removal of the eye.
Toxic Plants to watch out for in Autumn
Red leaf maple is very toxic to horses (mostly the wilted leaves from the trees). The toxic compound is unknown but it causes rapid hemolytic anemia (destruction of red blood cells). Signs of poisoning include lethargy, discolored urine and jaundice gums.
Black cherry, laurel, johnsongrass, choke cherry, and photinia contain cyanide.
Other situations where there can be plant toxicity are after brush clearing and in diet pens with no forage where horses can become bored and will eat anything.
Call your local vet if you have any concerns.
Special thanks to Dr. Paul Schwab, DVM, Kulshan Veterinary Hospital for this information
