"Horse eyes are awesome," began Amber Labelle, DVM, MS, Dipl. ACVO, assistant professor and veterinary ophthalmologist at the University of Illinois Veterinary Teaching Hospital. "But excessive tearing is not awesome."
During a presentation at the 2013 American Association of Equine Practitioners' Convention, held Dec. 7-11 in Nashville, Tenn., Labelle took an up-close look at excessive tearing in horses and what potentially serious conditions it might point to.
The Nasolacrimal System
"They eye can only do so many things—it squints, tears, and gets red; it's a three-trick pony," she explained. And the horse's nasolacrimal (or tear) system and tear film play a very important role in maintaining ocular health. The tear film works by:
- Providing oxygen and nutrients to the corneal epithelium;
- Removing debris and waste products from the cornea;
- Keeping the ocular surface lubricated; and
- Allowing light to pass from the external environment directly into the eye.
"The old adage 'no foot, no horse,' in certainly true; its ocular equivalent is 'no tear film, no eye,' " Labelle said.
The horse's tear film is replaced regularly throughout the day. When its replaced, the used tears drain through the nasolacrimal system. Labelle explained that the nasolacrimal system includes the ocular puncta, the cacaliculi, the lacrimal sac, the nasolacrimal duct, and the nasal puncta. The ocular puncta are like the drain that takes tears away from the surface of the eye, the nasolacrimal duct is the pipe that tears drain through, and the nasal puncta is the final drain where the tears exit into the nose.
"Think of it like a bathtub," Labelle said. "Tears come out of the 'faucet,' the canaliculi and lacrimal sac are the tub, and the nasolacrimal duct is the drain."
If any of those structures malfunction, excessive tearing will occur.
Assessing Horses with Excessive Tearing
When it comes to excessive tearing, "you're either making too many tears or they're not draining away," Labelle said.
To assess the situation and determine which of the two options a veterinarian is faced with, Labelle suggested performing a few diagnostic assessments.
A nasolacrimal duct lavage (also called flushing the tear ducts) is used to test the system's patency (whether there's a blockage) and said veterinarians can use computed tomography or MRI to evaluate the nasolacrimal system's state, as well.
Finally, she described a Jones test, in which the veterinarian instills fluorescein stain on the ocular surface and waits to see how long it takes for the stain to come out the puncta in the horse's nose.
"This test is widely variable and not overly reliable," Labelle said. "Don't automatically think a negative test (if no fluorescein appears) means that the horse has an obstruction—it could be normal for the horse."
Once the veterinarian has completed an eye exam, he or she can start narrowing the possibilities of what could be causing the excessive tearing.
If tear overflow appears to be the problem, Labelle said it could be caused by "pretty much any ocular discomfort."
"Do a thorough eye exam, look for the painful reason, and consider environmental irritants," such as dust, wind, allergens, and ultraviolet light, Labelle said. Then, implement treatment as needed.
Decreased drainage could be caused by a wider variety of problems, Labelle said, including:
- Congenital punctal atresia—Horses with this condition have no nasal puncta, Labelle said. The condition is most commonly identified in young horses with a comfortable eye. Labelle said this is the most common nasolacrimal disease, but is generally uncommon. Veterinarians can treat congenital punctal atresia by placing a stent to facilitate drainage.
- Functional duct obstruction—In this condition, something, such as debris or a foreign body, obstructs the nasolacrimal duct. Affected horses generally have a comfortable eye, but are unable to flush tears through their nasolacrimal duct, Labelle said. Treatment includes flushing the duct manually, administering systemic anti-inflammatories for 10 to 14 days, and, in severe cases, potentially surgically removing the foreign body causing the obstruction.
- Malpositioned globe—A smaller-than-normal eyeball or an eye that is sunken in the skull could result in a malpositioned globe and, subsequently, problems with clearing irritants—and tears—from the surface. Labelle said treatment options include improving body condition (which could improve the globe's position) and diligent facial hygiene.
- Ocular punctal occlusion—The final condition Labelle described involves chronic conjunctival inflammation that leads to ocular puncta fibrosis and occlusion or a birth defect. This rare condition is treated via surgical creation of a new puncta.
Excessive tearing could suggest a number of potentially serious equine eye conditions. Veterinarians should examine cases carefully and then determine an appropriate treatment course.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.