Equine eyes endure many challenges to stay healthy: low-hanging branches, exposed nails in stalls, disease-carrying flies as well as fungal and bacterial infections. Unfortunately, eye injuries or illnesses in horses usually are not caught as early as eye cases affecting dogs and cats, say leading veterinary ophthalmologists.
"Dog and cat owners tend to look closely at their pets’ eyes every day, but owners of horses might not have contact with their horses out in the field for a week or so, or merely glance at their eyes from a distance,” says Steven Hollingsworth, DVM, Dipl. AVCO. He is chief of ophthalmology services at the School of Veterinary Medicine at University of California, Davis, and treats the eyes of small and large animals.
"As a result, the horse eye cases that come to us for treatment tend to be much worse than cases involving dogs and cats.”
A horse that is blinking or tearing excessively, has reddened or swollen eyes or is rubbing the eye against his foreleg or a post must be seen immediately.
The top five eye conditions affecting horses are
* Traumatic injuries
* Equine recurrent uveitis (ERU)
* Corneal disorders
* Squamous cell carcinom
"The big three—ERU, squamous cell carcinoma and corneal disease—in addition to trauma, represent well over 90 percent of equine eye cases we treat,” says Dr. Hollingsworth.
Claire Latimer, DVM, Dipl. ACVO, a consulting ophthalmologist at Rood and Riddle Equine Hospital in Lexington, Ky., agrees. "Most of what I see relates to trauma, from lacerations to contusions or infectious traumas to tissues, such as corneal ulcers or equine recurrent uveitis.”
Traumatic injuries range from eyelid and corneal lacerations to the presence of foreign objects under the eyelid, or worse, embedded in the eye. Common trauma causes are the eyes exposed to dust, plant material, whipping tails of other horses, exposed nails in stalls and low-hanging branches. Without prompt treatment, some of these traumas can lead to secondary infections.
ERU remains one of the most common—and challenging—conditions to treat and can lead to blindness. The three types of equine ERU are classic (affecting the front of the eye), insidious (or subclinical) and posterior (in the back of the eye).
Also known as moon blindness, ERU is an autoimmune disease characterized by excessive squinting, redness, cloudiness and tearing that increase in frequency and in severity.
"The big problem with ERU is that we don’t fully understand it or what conditions keep it active in a particular horse, and there is no cure for it yet,” says Dr. Latimer.
Conventional treatments include the use of topical or systemic non-steroidal anti-inflammatory drugs and corticosteroids to lessen the ocular damage and inflammation. In some cases, surgery is necessary.
Hollingsworth reported that UC Davis is doing preliminary studies on how to use stem cells to possibly combat ERU, but the research is still in its infancy.
"Sadly, I’ve seen ERU cases in just about every kind of horse, but Appaloosas are more pre-disposed,” he adds.
Ulcerations top the list of corneal conditions. The cornea is made up of collagen fibers and has four main layers. It lacks blood vessels, which would aid in combating an infection, and that puts it at risk for bacterial or fungal infections, Hollingsworth says.
"Corneal ulcers need to be treated aggressively with topical antibiotics,” he adds. "For horses with painful eyes, sometimes a tube called subpalpebral lavage is placed under the eyelid to apply topical solutions every other hour, around the clock.”
Squamous cell carcinoma is the most common form of ocular cancer in horses. The tumor tends to develop on the surface of the eye, on the third eyelid or within the eyelid, yielding masses that like look like warts. An equine veterinarian may use radiation or cryotherapy (freezing) to remove the mass and removal of the eye may be necessary.
Horses can also develop cataracts. Cataracts are generally treated with surgery.
Horses rely on their large, oval pupils and monocular vision to keep tabs on their surroundings with a nearly 360-degree field of view. Keeping their eyes healthy is crucial to their overall well-being.
"I recommend equine veterinarians first stand back and look at the entire horse and get the bigger picture first,” says Latimer. "Look for symmetry, discharge, swelling, position of the eyes and then move in to see if the lids are normal, if the cornea is clear or cloudy. Think through the order of diagnostic tests you want to perform in the safest order.
"If you need to get a culture, for example, you do not want to put any medications on the eye first or topical anesthesia, because they can impair the growth of the culture and give you a false negative.”
To aid in the diagnosis and treating of eye conditions, Latimer recommends that equine veterinarians have the following equipment on hand when examining a horse: opti-visor for magnification, otoscope, culture swabs, focal light source, glass slides, fluorescent stain strips, topical anesthesia, agents for sedation, thumb forceps to grasp the third eyelid to check for foreign bodies, Schirmer tear test strip, saline and sterile eye wash.
To protect horses’ eyes, Latimer recommends fitting them with fly masks and keeping stalls clean.
"Fly masks protect them from scratches on the cornea caused by swatting tails or flies, but it is important to look under the fly mask daily to make sure that there isn’t any object that could rub against a horse’s eye and cause injury,” Latimer says.
"Stalls need to be cleaned regularly to decrease the amount of dust exposure and stalls, and paddocks need to be inspected to ensure that they are free of any sharp objects that can protrude into a horse’s eyes.”