October 23, 2017

Dry Eye in Dogs

A close look at keratoconjunctivitis sicca, including research on new treatments that could be curative for this uncomfortable and often chronic condition.
By Don Vaughan
When Wanda Presnell, owner of a dachshund rescue in Raleigh, North Carolina, took custody of 10-year-old Precious in early January, the dog was riddled with health problems, including a urinary tract infection, back issues, heartworms, and, perhaps most troubling, severe bilateral dry eye, which was originally believed to be an infection.

“Her eyes were terribly matted,” Presnell recalled. “There was a pus-like discharge and irritation in both eyes, and she was in severe pain.”

Presnell took Precious to Magnolia Veterinary Hospital in Raleigh, where Jon Dick, DVM, confirmed a diagnosis of dry eye and prescribed tacrolimus aqueous drops.

“It worked great on the left eye,” Presnell said, “but the right eye did not respond at all. A veterinary ophthalmologist in Cary, North Carolina, prescribed tacrosporine NCT, but after a couple of months we saw that it was not working either.”

Presnell is still conferring with her veterinary care team to find an effective treatment for Precious’s right eye. In the meantime, she cleans Precious’s eyes 2 or 3 times a day, which eases the dog’s discomfort and makes it easier for her to see. “This is the most significant case of dry eye I’ve had to deal with,” Presnell said. “It’s a real problem.”

Prevalence, Causes, and Clinical Signs
Dry eye, known clinically as keratoconjunctivitis sicca, is almost exclusively a canine health issue, noted Brian Gilger, DVM, MS, DACVO, DABT, professor of ophthalmology at North Carolina State University (NCSU) College of Veterinary Medicine in Raleigh.

Around 5% of dogs will have some level of dry eye during their lifetime,” he reported. “It is seen far less commonly in cats and is almost unheard of in larger animals.”

Michala de Linde Henriksen, DVM, PhD, DACVO, assistant professor of comparative ophthalmology at Colorado State University College of Veterinary Medicine and Biomedical Sciences in Fort Collins, attends to around 20 cases of dry eye a month, including diagnoses and rechecks. The condition can affect all dogs, she noted, but tends to afflict certain breeds more than others, including shih tzus, Boston terriers, English bulldogs, cavalier King Charles spaniels, and West Highland white terriers.

“We believe that the autoimmune type of dry eye is a hereditary disease in specific breeds, but we have not yet found the gene for it, except for the cavalier King Charles spaniel,” Dr. Henriksen said. “The gene for curly coat syndrome and dry eye has been identified by a research group with the Animal Health Trust in Kentford, United Kingdom. They also determined that this gene does not cause dry eye in any other breed of dog." 

The signs of dry eye are fairly telltale, reported Dr. Gilger, and include reduced tear production; a thick, mucoid discharge; redness and irritation of the eye tissue; and noticeable discomfort that is sometimes indicated by squinting. “Clients often think their pets have an eye infection, but it’s really dry eye developing,” Dr. Gilger noted.

Pet owners may question a diagnosis of dry eye because of the discharge—how can the eye be dry when there’s so much fluid?—and it’s the veterinarian’s responsibility to explain that the discharge is the result of irritation and is not an ocular lubricant.

Forms of Dry Eye
Spontaneous dry eye is the most common form of the condition, but there are others, known as qualitative tear film deficiencies, that are characterized by a lack of mucin or other important tear components, Dr. Gilger said. In addition, a small percentage of dogs are born with an ocular defect that inhibits tear production in sufficient quantity. Although relatively rare, the condition is considered serious because it does not respond to conventional treatments.

Most cases of spontaneous dry eye are immune mediated, Dr. Henriksen said, which means the patient’s immune system is attacking the lacrimal glands and adversely affecting tear production. In others, the nerve to the lacrimal gland may stop working, causing tear production to cease.

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