Advances in equine eye care

Part one of two…

The more researchers study equine physiology, the more evidence suggests that so-called bad behavior could be as much physical as training and behavioral. Back pain, for instance, might be the root cause of many under-saddle issues. Now, equine vision problems are emerging as the culprit behind some cases of spookiness and other undesirable behaviors.

In a lecture at the Dressage at Devon, PA, show in September, Chelsey Miller, DVM, a resident in veterinary ophthalmology at the University of Pennsylvania’s New Bolton Center in Kennett Square, described some of the exciting advances in her field.

Cataracts

A cataract is a clouding of the lens of the eye, giving the eye a clouded, milky-white appearance. Most people are familiar with the term because almost all humans develop cataracts as they age.

Equines can also develop cataracts, which in horses aren’t age-related, Miller said. Cataracts can cause anything from light sensitivity to nearly complete blindness. Some horses manage just fine with cataracts, even when one eye is virtually blind; a cataract is a greater liability in equestrian disciplines requiring keen depth perception, such as jumping and polo. (Oddly, though a one-eyed racehorse is “legal,” the Hackney-pony and Paso Fino breeds mandate two “visual eyes” for competition eligibility, she said.)

Surgical removal of cataracts in humans is a relatively simple office procedure. The surgery is more complicated in equines because general anesthesia is required, Miller explained. In fact, cataract removal is the most complex procedure in veterinary ophthalmology, she said.

The process is called phacoemulsification. A probe vibrating at ultrasonic frequencies liquefies and breaks up the cataract, which is then vacuumed out of the eye, Miller said.

In the past, the required minimum two to three months of post-operative care and regular medicating of the eye was practically as challenging as the cataract surgery itself, Miller said. During this time, horses often get resentful of having the eye area handled, and the continual manipulating of the eyelid can damage the surgical site. Thankfully, today veterinarians can install a temporary catheter that delivers the eye meds via a tiny tube, no direct handling necessary. If the horse is quiet and not inclined to rub his head, he can even be hand-walked or turned out in a small pen with a fly mask on during the rehab period, she said.

Miller cautioned that cataract surgery doesn’t give the horse perfect vision. However, veterinary ophthalmology researchers at North Carolina State University are looking into the use of an artificial lens to improve near- or farsightedness, she said. Experts use a technique called retinoscopy, in which different lens refractions are used to estimate a horse’s vision, to help determine the degree of near- or farsightedness. (Most horses are farsighted, she said.)

Equine cataract surgery isn’t undertaken lightly. First, there’s the cost, which can run into the thousands (Miller was reluctant to state price ranges for the record). Second, there are risks of complications. For the latter reason, Miller said, most veterinarians are reluctant to do surgery if the horse has some vision.

“It’s possible you could start with an eye with some vision and end up with no vision,” she said. F

Watch next week’s paper for part two of this series.

–thehorse.com