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.


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.