Ophthalmology for Equine Road Warriors
"I have a special interest in eyes, but they're only about 5% of my work," began Ann Dwyer, DVM, of Genesee Valley Equine Clinic in Scottsville, N.Y., at the Western Veterinary Conference Feb. 20-24 in Las Vegas, Nev. "I'm a practitioner, not a researcher.
"The life of the road warrior (ambulatory practitioner) is fun, challenging, and never boring," she said, implying that these practitioners see a wide range of health issues and are challenged to provide an initial diagnosis and treatment of these myriad problems. "Some problems will always have to be referred to specialists, but the average practitioner can diagnose, treat, and monitor 85% of the eye problems that are seen in the field."
This presentation centered on equine ophthalmology evaluation, tools, and diagnoses for the ambulatory practitioner--i.e., one working in the field without access to referral clinic-level equipment, staff, and facilities. She first focused on the equipment that every practitioner should keep in the truck for eye examinations. "One of your most important tools is a Mag-Lite--90% of what you need to see can be seen with a good penlight," she commented. "And a digital camera is invaluable for recording problems. I now have over 4,000 images in just over a year (of using the camera); I can take a picture, go home, and compare it to books, etc."
In terms of ambulatory ophthalmology practice, she noted that clean patient preparation was essential. "Glove for diagnosis and treatment: Barns are dirty!" she stated. She also discussed equipment and techniques for various eye tests, and sedation protocols for eye exams and procedures.
"Clients consult you (for an eye examination) because a horse is spooky or has jumping or other performance problems, or because his eye(s) looks wrong," Dwyer stated. "For once, you are the expert with eye problems. No one will come and say the horse needs an eye massage," she said with a laugh.
"To get competent (at eye exams), just start looking at the eyes of every horse you see," she suggested. "Do a Mag-Lite exam while vaccinating a horse. Be systematic, slow down, think anatomy. Maybe there is a really obvious problem, but look at everything else, too. Look at both eyes, assess symmetry, assess visual axis (the central line that light travels to get into the eye--essentially the "center" of the eye--this part must be clear in order for vision to be intact), cranial nerve function, dazzle (a bilateral, or in both eyes, partial blink that occurs if a bright light is shone into one eye; this tests the presence of an intact nervous connection from the eye to the brain and back to the lids), pupillary light reflex, and menace reaction (reaction to something coming near the eye).
"You can also do a blindfold test, which assesses unilateral vision," she explained. "Cover one eye with a towel, turn the horse loose in an aisle with a bucket maze, and coax him to walk toward food. Repeat on the other eye and compare. If the horse has a visual problem with one eye, this will be extremely obvious when you cover the good eye."
Owners calling about horses with painful eyes or eye trauma should be told to have a dark examination area available, and to have four bales of shavings or hay ready to use as a head rest for standing surgery/diagnostics, she said.
"Train owners to call for same day examination on any lids that show severe swelling," she urged. "Prognosis of orbital and periorbital disease varies with the etiology, but prompt assessment, vigorous therapy, and judicious referral will optimize outcome."
Medications for equine eye problems were another focus, as there isn't a wide range of medications labeled for use in equine eyes. Compounding and use of available human medications was discussed in detail, as was the proper use of and instrumentation for delivering these medications. Dwyer added that writing out treatment schedules for clients (rather than expecting them to remember the schedule) is very helpful.
"Also, some medication use (for equine eye problems) is off label, so discuss it with the client," she recommended. For example, she said that the Silvadene (silver sulfadiazine) label says not to use it in eyes, which can be very alarming to the client, but this medication has stood the test of time for therapy of certain fungal infections of the cornea.
With prescription medications, "It pays to shop!" she said. "Pharmacy prices vary widely, and WalMart is often very competitive. Dispense topical meds in a write-on bag. Write out the treatment schedule for that medication for the next several days by making circles on the bag indicating the number of treatments for each day of the week. This simple step increases compliance and keeps the medication clean."
When instructing a client on how to medicate a horse's eye with ointment, Dwyer gave the following recommendations: "Have clients feel the orbit rim and look for the crease in the lid. Tell them to put a dry finger on the crease above the eyelashes and push the lid a little under the orbital rim to hold it open, and apply a quarter-inch strip of ointment."
She added that masks (fly masks that also block sunlight to some degree) are helpful for treating injuries, solar blepharitis (eyelid inflammation), and uveitis.
Common Problems and Diagnosis
"The horse's eyes are at the widest part of his head, so when horses put their heads where they shouldn't be, the eyes are going to get hurt," Dwyer stated. "Orbit (eye socket) injuries can occur in the starting gate, or in pasture scuffles (kicks). Miniatures and Thoroughbreds seem especially prone to these injuries. If an (unexplained) eye swelling persists, think about a fracture with or without infection or a foreign body."
When trying to diagnose an eye problem, she noted that radiographs might or might not show a fracture, and that multiple angles might be needed to find one. Ultrasound might be helpful for investigating injuries as well.
Common eye problems she discussed included the following:
- Suture line periostitis (inflammation of the edges of bones that make up the skull) appears as non-painful, firm bumps in the periorbital region (near the eye). "It has a characteristic radiographic appearance, and there is no therapy," she explained. "It may self-resolve over time; tell the client not to worry about it."
- Orbital tumors are pretty rare, she said. Ultrasound both eyes to look for asymmetry, and the prognosis for completely removing the tumor may be guarded. "Be prepared to do an enucleation (removal of an eye)," she said. "And it may bleed far more than a normal enucleation."
- Eyelid injury: "The major cause of eyelid injury is those J-shaped hooks on bucket handles--I tell clients to tape up the hooks or buy buckets with button handle attachments," she stated. "Bucket handles probably cause 80% of the eyelid tears we see. Lid repairs are done standing." Lighting is often terrible in barns for any kind of eye procedure, so she uses a halogen trouble light that hooks on the wall. "Owners may faint (during a lid repair or other eye procedure); have them stand on the other side!" she warned. Delayed lid repair is possible; "The eyelid region is very mobile, and you can achieve good results with these if you take care and plan," Dwyer said. "As long as the blood supply is there, the eye region is very plastic. You can make a horse much more comfortable by fixing his eyelids."
- Lid neoplasia is not rare, with squamous cell carcinomas (SCC) and sarcoids the most common tumors, she said. "There are many treatment options, but if untreated, progressive growth may threaten the eye or even the horse's life. Biopsy of these masses is important, as many things that look alike are very different at the cellular level."
- SCC are locally invasive and can spread to the orbit if untreated, she said. Referral options include excision with reconstruction, hyperthermia (heat ablation), cryotherapy, beta irradiation with strontium 90, brachytherapy, and intralesional chemotherapy (cisplatin).
- Sarcoids of lids can really be a mess mainly because they tend to grow slowly, progress, and really hamper lid function, she noted. "They start as little things like a little wart or thinning of the hair," she reported. "Is there a genetic predisposition? Probably. They're caused by bovine papilloma virus, which is spread by flies." She said on-farm treatment is possible, but many of these horses are best referred for laser ablation or other treatments.
- Trichiasis is a problem in which the eyelashes are bent in toward the eye, she said. Electroepilation (hair removal using electricity) is the treatment, and the problem is usually secondary to eyelid trauma. "It's tricky and hard to treat," she commented.
- Entropion (in which the eyelid rolls in toward the eyeball) is most common in neonates, she said. With the foal under light sedation, sutures can be placed to roll the eyelid back out. It normally will remain correctly positioned after sutures are removed a few weeks later.
- In summer, horses might present with a huge swollen eyelid, usually unilateral (in one eye), she reported. "I think these are insect bites if they're fluorescein negative (indicating that no corneal ulcer is present)," she said. The swelling is easily treated with topical anti-inflammatory therapy.
- Another common problem is what she terms burdock keratopathy. "The tiny barb on burdock (pasture weed) gets imbedded in the third eyelid or upper lid and irritates the cornea," she explains. "Burdocks were the inspiration for Velcro--the plant ends in a spiny ball covered with barbs that have microscopic barbs on their tips." Treatment involves debriding the eyelid or affected conjunctiva to remove the embedded barbs.
- If the nictitans or third eyelid prolapses bilaterally (in both eyes), think tetanus or an acute attack of hyperkalemic periodic paralysis, she said. Think Horner's disease (a nerve condition causing a droopy eyelid, constricted pupil, and sunken eyeball) if it's unilateral. Nictitans tumors can be excised, she said.
- Meibomanitis refers to cheesy abscesses of the meibomian glands (oily glands in the eye that are also called the tarsal glands; these produce sebaceous material that contributes to the tear film). "You won't cure these things; you can curette and incise them, but they'll always come back," she warned.
- Solar blepharitis often affects Appaloosas, Paints, Ponies of the Americas, and other horses that lack of pigment at the lid margin. For these, "Use a light-blocking fly mask and topical treatment," she said.
- Blocked tear ducts are an over-diagnosed problem, she said. "These may be secondary to a sinus infection, or anatomical problem--always look for the primary cause of the tearing," she said.
- Inadequate tear film in horses does happen, she said. It causes a dull appearance to the eye and pain. It might be hard to treat, but Optimmune (topical cyclosporine A) or artificial tears in gel can help.
- Scleral hemorrhage is a benign condition in newborns secondary to birth trauma, she said.
- Conjunctivitis is common, but not as a primary diagnosis, she stated. It's usually secondary to inflammation from exposure, allergy, uveitis, corneal disease, etc.
About the Author
Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.
POLL: Tack Shopping Choices