Q:I've read that horses can be near- or farsighted. Given how important good eyesight is for social interactions and performance in some sports, do horses ever receive corrective vision surgery? Many people with poor eyesight are treated with laser eye surgery; is that possible for horses? Or do those with poor eyesight simply compensate with their other senses?
A: Horses, like people, can suffer from a variety of optical aberrations that affect visual acuity. The common eye problems you allude to that can affect the eyes of both people and horses are refractive errors, such as nearsightedness (myopia) and farsightedness (presbyopia), and astigmatism, which affects the eye's ability to focus. A veterinary ophthalmologist can perform retinoscopy to assess a horse for abnormal vision.
Fortunately, most studies report the majority of equine eyes are nearly normal in function. A horse with normal vision (emmetropia) can see almost 360 degrees around with just two small blind spots: The first begins at the forehead and comes to a conelike point about three feet in front of his body. The other is right behind his head, reaching over his back and directly behind his tail.
When refractive errors occur, images are not focused properly on the retina, the light-sensitive tissue in the back of the eye's interior that transmits signals through the optic nerves to the brain. Other significant factors that can affect a horse's vision include infectious and noninfectious corneal disease, uveitis and cataracts. These diseases can be treated successfully medically and/or surgically, but scarring and inflammatory changes can result in permanent refractive errors.
So, in answer to your question, yes, horses can have refractive errors and abnormal vision just like people, but as a matter of anatomical and other considerations, LASIK surgery and corrective eyewear are not practical for use in the horse. In general, many horses can adapt and compensate
quite well with visual adversities and are able to lead normal lives, so we rarely intervene with corrective measures. An exception might be following cataract surgery, when an artificial or intraocular lens is placed in the lens capsule to improve the patient's refraction.
Early detection and intervention increases the chances of successful treatment of eye diseases that could result in refractive errors, so have your veterinarian address any suspected eye problems promptly.
Brendan G. Mangan, DVM, MS, DACVO
University of Florida
College of Veterinary Medicine
This article first appeared in EQUUS issue #426.