Our guest for this podcast on equine eye problems is Dr. Nicole Scherrer. She is a Diplomate in the American College of Veterinary Ophthalmologists (DACVO) and an Associate Professor of Clinical Large Animal Ophthalmology at the University of Pennsylvania School of Veterinary Medicine.

(Editor’s note: The content of this podcast is the expert’s approach to the topic. Please consult with your practitioner if you have questions.)

Corneal Ulcers

Scherrer said slow-healing corneal ulcers are important eye issues in senior horses because the cornea is also aging. That means any issues won’t ‘rebound’ as quickly as if they happened in a 2-year-old. She also mentioned co-morbidities that occur in many older horses.

“A lot of them [senior horses] have Cushing’s [PPID],” said Scherrer. “We all we know these horses are at higher risk for infection in many areas of the body, and the eye is one of them.”

Immune-Mediated Diseases

Scherrer said the two diseases that are seen most commonly are called immune mediated keratitis and equine recurrent uveitis (also known as moon blindness).

“Both of those diseases are immune associated,” she explained. “And the more the more episodes the horse sees, the more damage that there is to the eye.”

She also said that damage can add up overtime in lightly pigmented horses. “So, any type of pink skin around or on the eye [means] they’re at an increased risk for cancer. That’s one where the more UV light the horse sees over its life, the higher the risk for the cancer developing.”

What is Equine Recurrent Uveitis?

Moon blindness is one of the most common eye issues veterinarians see in horses. “It makes up about one-quarter of the cases that we see in our ophthalmology population,” said Scherrer. “And probably there are way more out there than we know of. The true incidence rate of it varies anywhere from 1 to 25% depending on which source you’re looking at.”

She explained that equine recurrent uveitis is the body’s own immune reacting against the eye. “Think about it as the immune system has decided that it is trying to attack and help the body, but it’s attacking something that is actually part of the body,” Scherrer said. “So it just gets misdirected.”

She said the goal with uveitis is to try to control that immune response so that as little damage happens to the eye as possible.

Scherrer said historically, there was not a good understanding of what caused moon blindness in horses. Many different theories were posed. One of those historic theories was that the eye issues were associated with changes in the phase of the moon. Thus the name moon blindness.

Treatment for Moon Blindness

“We want to prevent the episodes from every happening again,” stressed Scherrer. “We’re going to treat either with a daily medication that could be something by mouth, or more commonly, something actually like an eye ointment onto the eye.”

She said there are a couple of surgical procedures that might help to reduce or eliminate the need for daily medications.

However, “we’re never going to make the disease go away,” she noted. “But, they’re not having active episodes. And by active episodes, I mean squinting, tearing, redness, and cloudiness.”

Differentiating Uveitis and Corneal Ulcers

“It gets a little bit tricky because squinting, tearing, redness, and cloudiness are basically the signs we see for any ocular disease,” said Scherrer. “If your horse has a history of equine recurring uveitis, you can make a pretty educated guess that it’s probably an episode of uveitis.

“What gets tricky is that the difference between an episode of equine recurrent uveitis and a corneal ulcer,” she warned. “They’re basically going to look the same to an owner.”

She said the problem is that, “if we go and put a steroid in the eye, which is an appropriate treatment for equine recurrent uveitis, that would be the exact opposite treatment that we would want to do for a corneal ulcer.

However, she added, you can have an uveitis episode and a corneal ulcer at the same time.

“That’s why it’s important to call your veterinarian,” she advised.

Final Words

Scherrer offers many other tips on equine eye care in this podcast. One thing she wanted to mention is that some older horses have vision issues as they age. This might mean diminished vision, or even blindness.

“They can still leave really happy lives,”she stressed. “Horses with vision loss need a little bit of help.
Maybe kinder friends in the field with them and making sure that their field is a very safe place.

“I have a lot of patients that have no vision at all, and owners have nice flat paddocks for them,” she noted. “That might mean changing the footing around any trees or maybe the gate in and out so that they’re able to navigate well.

“So, visual or not, older horses can do incredibly well,” she stressed. “The nice thing about the older horses is with that comes some wisdom in most cases. “They are usually pretty adaptable because of that, but circle back to anytime you have concerns vision wise or ocular pain wise call your vet even if it’s after hours. You can even run the question by them and just make sure that it’s not something that they need to come out on emergency for. Maybe it’s just something that they can see at their next visit, but it’s always worth asking your vet.”

Scherrer also recommended the UV fly masks that can block up to 90% of UV light. “But if they are wearing a mask, make sure to take it off and check their eyes at least once a day,” she added.

Further Reading