Glaucoma is a painful eye disease that can cause blindness in both animals and humans. In Shiba Inu dogs, the condition is especially concerning because the breed is predisposed to narrow or closed iridocorneal angles from birth, making them more likely to develop the disease. While treatment can only slow glaucoma’s progression, researchers are working to uncover its genetic causes and develop reliable tests for early detection.
Keiko Miyadera, an associate professor of ophthalmology at Michigan State University’s College of Veterinary Medicine, has spent her career investigating hereditary diseases in animals. Here, she discusses her research on glaucoma in Shiba Inus, the challenges of studying the disease and how breeders are playing a vital role in advancing solutions.
What is glaucoma and how does it affect Shiba Inus?
The Shiba Inu is one of Japan’s most popular dogs and has become beloved globally in recent years with a reputation for being willful, protective and fiercely loyal. However, this species is unfortunately also prone to a condition that impacts both dogs and humans: glaucoma.
The Shiba Inu breed is predisposed to narrow or closed iridocorneal angles from birth. This eye condition occurs when aqueous humor, the fluid that fills the front chamber of the eye, cannot effectively drain from a small opening between the iris and cornea, called the iridocorneal angle. Increased pressure within the eye causes acute pain and a “cloudy” appearance. Eventually, accumulated damage to the optic nerve leads to irreversible blindness. Standard treatment with eye drops and, in some cases, surgery cannot effectively cure glaucoma — it can only slow the progression.
Because glaucoma is painful and blinding, we often end up needing to remove the affected eye for the dog’s comfort. It is unfortunately common to see Shiba Inus with one eye. It is traumatic for dogs and their families, so Shiba Inu breeders and owners are interested in solving this issue.
Is a simple DNA test available to predict which dogs will develop glaucoma?
Given the known association between the iridocorneal angle and primary glaucoma in Shiba Inus, one might expect a simple DNA screen for genetic markers of abnormalities could identify dogs at risk. But finding those markers is not that easy.
Ideally, a single DNA test will perfectly predict whether a dog will develop glaucoma. For such Mendelian diseases — ones where only a single genetic variant always causes the disease — we would analyze a few dozen cases and control dogs of the same breed. But glaucoma in the Shiba Inu breed has turned out to be genetically more complex, requiring genotyping of hundreds of dogs that have been carefully examined and classified according to the appearance of their eyes.
How do you currently test Shiba Inus for glaucoma risk?
One diagnostic tool, gonioscopy, allows veterinary ophthalmologists to examine the iridocorneal angle. It is currently the only reliable way to identify dogs born with the risk of developing the type of primary glaucoma common in Shiba Inus. But Shiba Inus are not the easiest of breeds to do gonioscopy on. The gonio lens used for the exam does not fit well on their eyes — one breeder described seeing the gonio lens slipping off the dog’s eye and flying across the room. We tried all the gonio lenses available and found that one designed for infants worked well for Shibas.
What role do breeders play in this research?
This work has largely been led by passionate breeders. Breeders have invited us to collect data — and provide valuable eye exams — at national dog shows and even at their homes. These exams yield insights on individual dogs’ health that help breeders care for their Shibas and educate pet owners. These breeders and owners are helping our understanding of the disease and the dogs that are at risk. The ability to test puppies would enable breeders to identify which puppies should be kept in a breeding program versus their placement as pets. As ambassadors to the breed, many breeders are determined to do whatever they can to help end this painful, blinding disease.
How could this research impact both dogs and people?
Ongoing research with new findings is on the horizon that can benefit both dogs and people, including the possibility of developing tailored treatments that directly target the disease process of glaucoma. Every exam and every DNA sample brings our team one step closer to protecting vision in both dogs and humans.
