Last week we discussed bovine and small ruminant ophthalmology. This week, let’s take a peek into the equine side of things.
Unlike cattle, sheep, and goats, where the majority of eye issues are infectious, the majority of equine eye problems I see are trauma-related and result in corneal ulcerations.
It is my scientific opinion that horse eyes seem predisposed to getting poked out. This is most likely due to their anatomical location, which is namely right on the corners of the head, sticking out like headlights on an old VW Bug. Sharp objects apparently roam the Earth searching for horse eyes.
One of the most common culprits is, unfairly, the very food they eat. Long wiry pieces of hay shooting out of the trough or hay net are almost always in the "Usual Suspect" lineup when we play the game, "Who Poked Out My Horse’s Eye?"
As with cattle and small ruminants with inflamed and infected eyes, horses with corneal ulcerations exhibit similar signs. Horse owners will observe a forcefully closed eye, excessive tearing, with perhaps some head shyness or avoidance of light, depending on the disposition of the horse. As hours pass, the cornea may become cloudy, and white or yellowish discharge instead of tears may weep from the eye.
The beginning of any emergency equine exam starts with sedation and a nerve block of the upper eyelid to allow me to open the eye wide. Then, if I suspect trauma and corneal damage, I’ll apply a special stain to the eye. This stain will glow neon green if the delicate tissue underneath the outer layer of the cornea is exposed due to ulceration. Sometimes the area of ulceration is literally the size of a needlepoint. But no matter what the size, ulceration is ulceration and requires treatment.
Most mild corneal ulcerations can be treated with topical antibiotic ointment and some pain medication. Others are more complicated. If the ulcer is large, healthy epithelial tissue sometimes has difficulty adhering to the cornea, and healing is non-productive. If this is the case, we sometimes have to scrape the eye to remove the old tissue, giving the new tissue something to adhere to.
Other times, the ulceration has allowed bacteria inside the eye, setting up what is called a stromal abscess. These can be very difficult to treat, requiring intensely frequent applications of multiple types of medications. At the very worst, an ulcer can be deep enough to rupture the eye. This is why eye issues are always an emergency, since you can never be sure at first exactly how deep the problem really is.
Eyelid lacerations are another extremely common equine eye problem. Like the ubiquitous hay stalk waiting to cause a corneal ulcer, another common barn object is frequently the cause of dangling eyelids: the hooks at the ends of water bucket handles. These curved metal pieces on the sides of hanging buckets just seem to jump out at horse eyes and grab on to upper eyelids for dear life, resulting in a gruesome find for the owner the next morning.
Luckily, eyelid lacerations usually look much worse than they really are. They bleed a lot and swell a lot, making the horse look like he’s been in a bar fight involving brass knuckles and a switchblade. However, after sedation and nerve blocks and a little careful stitching with very fine suture material and a teeny tiny needle, the horse usually comes out of it looking much better. The only challenge is not letting the horse rub his head once the stitches become itchy a few days later.
Sometimes with an eyelid laceration, the owner will ask why I don’t just trim off the lacerated portion rather than sew it back on. The answer is that horse’s eyes are so big, they need all the lid they can get. Eyelids are the best protection the eyeball has against the pokey world and even a small missing portion can sometimes result in chronic eye irritation.
Although we’ve covered the traumatic cases of equine eye emergencies, we haven’t even touched on things like cancer of the eye and a weird thing only horses get called "moon blindness." Shall we say, stay tuned?
Dr. Anna O’Brien