WCVM scientists focus on moon blindness

Six years ago, Shelley and Ray Ruiters purchased an Appaloosa mare named Annie from friends who thought she would be a great fit for the couple.

It turned out that the Ruiters’ friends were exactly right. “From the first day I met her we just rode off on our own and she never missed a beat,” says Shelley.

About a year after Annie arrived at the Ruiters acreage near Saskatoon, Sask., her owners noticed tearing and squinting in her right eye. Soon after, the mare was diagnosed with equine recurrent uveitis (ERU) or moon blindness.

“I had absolutely no knowledge of this disease nor did any of my riding friends prior to Annie’s diagnosis,” says Shelly.

The Ruiters’ mare was suffering from one of the oldest known equine diseases and the leading cause of blindness in horses. Uveitis is swelling of the choroid, the area that supplies blood to the eye. ERU is characterized by chronic bouts of inflammation in the eye that causes ongoing damage — eventually leading to blindness.

Clinical signs of ERU include tearing, squinting and sensitivity to light. Veterinarians might notice lower pressures of fluid in the eye, an iris that is adhered to the lens, and small cataracts.

Annie’s struggle with the eye disease coincided with Shelley’s own diagnosis of breast cancer.

“Riding (Annie) settled my mind and prepared me for what was to come. Annie carried me safely two weeks after my surgery,” says Shelley, who derived strength from her horse.

“Anyone who has ever breathed into their horse’s nostril knows that nothing beats the smell of a horse when you are a little down.”

Shelley’s cancer is now in remission, but in May 2013, Annie developed a painful ulcer on her remaining eye that wouldn’t heal. The Ruiters had to make a difficult decision.

“On our last ride together, it was apparent that Annie had lost her confidence. Her vision was impaired, and she struggled to keep both of us safe,” says Shelley, whose beloved 12-year-old mare was euthanized this spring.

“I just couldn’t stand to see her suffer any more. I lost an amazing animal friend in the prime of her life who had no other existing medical concerns.”

Diagnosing ERU can be challenging, says Dr. Lynne Sandmeyer, a veterinary ophthalmologist at the Western College of Veterinary Medicine (WCVM). Before a diagnosis can be confirmed, clinicians must rule out other causes of uveitis including parasites, viruses, trauma or a rupture of the lens.

“The sad thing about it is that it can often be missed so that the animal can be going blind without anybody noticing,” says Sandmeyer.

There is no cure for ERU, and treatment focuses on minimizing inflammation in the eye. Lifelong treatments include anti-inflammatory drugs that are given as eye drops or orally to the horse. Another constant medication is atropine that causes pupil dilation. Dilating the pupil eliminates painful muscle spasms in the eye and prevents the iris from sticking to the lens.

“The downsides to continuous treatment are the need to treat the horse several times a day with topical medications as well as chronic use of oral anti-inflammatory drugs which can lead to gastrointestinal irritation, especially in performance horses,” says Sandmeyer. She is part of a long-term study of ERU along with her colleague, Dr. Bianca Bauer.

This year, the research team is gathering a history of ERU at the WCVM’s Veterinary Medical Centre by going through medical records in search of all suspected cases of ERU in the past 10 years.

Researchers are gleaning valuable information from the patients’ records such as the breeds and sex most affected by ERU, descriptions of disease progression, length of time before a confirmed diagnosis, and the time from diagnosis to euthanasia or eye removal surgery.

Appaloosas such as Annie are of special interest to the research team. In a study conducted over eight years (1987 to 1995), ERU-affected horses were tested and Appaloosas showed a 25 per cent prevalence for the disease. In comparison, other horse breeds only had a 10 per cent prevalence for ERU.

Sandmeyer and her colleagues recently discovered a gene known as “LP” (Leopard complex) that causes the Appaloosa to have the spotted coat patterns. They uncovered an association between horses having two copies of the LP gene and a disease in Appaloosa horses called congenital stationary night blindness (CSNB).

The WCVM researchers are now interested in determining whether there is a link between the LP gene and Appaloosa susceptibility to ERU.

The Ruiters are among the many horse owners who will be anxious to learn about the WCVM team’s findings after watching their own horse suffer from the devastating disease. ERU’s cause has yet to be discovered, and the WCVM research team’s first steps into studying the genetic component of ERU are critical if horses like Annie are to be saved in the future.

“The care of an animal with this condition can be exhausting and costly,” says Shelley. “We did it all because Annie was loved and appreciated.”

Laura Field of Holbein, Sask., is a fourth-year veterinary student who participated in the WCVM’s Undergraduate Summer Research and Leadership program in 2013. Visit WCVM Today to read more WCVM news.