The Shiba Inu, one of Japan’s most popular dogs, has become beloved globally in recent years—in large part thanks to its cute, fox-like face and instantly-recognizable curled tail. With a reputation for being willful, protective, and fiercely loyal, they are unfortunately also prone to a condition that impacts both dogs and humans: glaucoma.

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.

Dr. Keiko Miyadera, associate professor of ophthalmology at the MSU College of Veterinary Medicine, explains that the Shiba Inu breed is predisposed to narrow or closed iridocorneal angles from birth.

“Because glaucoma is painful and blinding, we often end up needing to remove the affected eye for the dog’s comfort. It is unfortunately not uncommon to see Shiba Inus with one eye,” she says. “It’s traumatic for dogs and their families, so Shiba Inu breeders and owners are interested in solving this issue.”

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,” explains Miyadera. “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.”

To expand the pool of clinical data, Miyadera’s current work involves examining dogs across the country. This type of work is not new to her.

She has been interested in the underlying genetics of hereditary diseases since she was a veterinary student at the University of Tokyo, where she investigated hereditary diseases in beef cattle in her hometown. As a student researcher, she also joined Dr. Kumiko Kato, then a staff ophthalmologist of University of Tokyo, on field work visiting dog owners and breeders across Japan.

“We were on the road a lot,” Miyadera recalls.

After earning a PhD in molecular biology at the University of Cambridge and completing an ophthalmology residency and postdoctoral research at the University of Pennsylvania (where she also served a faculty role), Miyadera continues to collaborate with Kato — expanding Kato’s work to include the U.S. Shiba Inu population.

And even though Miyadera is based at Michigan State, partnerships with Shiba Inu breeders have her on the road once again. While at the University of Pennsylvania, she met breeder Sandie Rolenaitis, who invited her and Kato to collect data—and provide valuable eye exams—at national dog shows

“We would basically live in a trailer, conducting eye exams all day, for several days,” says Miyadera.

One diagnostic tool, gonioscopy, allows veterinary ophthalmologists like Miyadera 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 Shibas pose a logistical challenge.

“Shiba Inus are not the easiest of breeds to do gonioscopy on,” explains Miyadera. “The gonio lens used for the exam doesn’t 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 in people worked well for Shibas.”

The breed’s famously strong-willed personality doesn’t help either. “Shiba Inus are not the most cooperative!” she laughs. “They do not always agree with us doing the exams, and that’s one of the reasons developing a DNA test that uses a simple cheek swab will be very helpful.”

A strong community of breed advocates has supported the work. Rolenaitis has been part of the Shiba breeding community for 35 years, and has brought home several from Japan to boost the breed’s presence in North America. Glaucoma has impacted multiple dogs dear to her.

“I know how detrimental and exhausting glaucoma can be,” she says. “I don’t want other owners to deal with this.”

She has gonioscopies performed on all her dogs and encourages those who adopt from her to support the research.

“I encourage Shiba owners to get a baseline exam,” she says, “and ensure their veterinarian owns a tonometer to check intraocular pressure. Get a gonioscopy so you know if your Shiba is predisposed to glaucoma early! Even though it mostly hits around seven years of age, early understanding of the risk matters.”

After Rolenaitis’s initial invitation, word of Miyadera and Kato’s work spread among the Shiba Inu breeder community, and they were invited to examine dogs at more shows. These exams yield insights on individual dogs’ health that help breeders care for their Shibas and educate pet owners.

“It’s imperative to be proactive and to become better informed on how to test for the risk of glaucoma, and how to properly care for the at-risk and diagnosed Shiba,” says Dovie Trotter, another breeder who recently invited Miyadera and Kato to examine Shiba Inus in the Colorado and Wyoming area.

And though gonioscopies can provide useful insight into a dog’s risk for glaucoma, an understanding of the genetic profile of at-risk dogs could lead to even better diagnostics and potential treatments. With a larger genetic database to analyze, researchers will be better able to pin genetic markers to risk factors and specific phenotypes, unraveling the mystery of why glaucoma seems to be so complex — and eventually developing a reliable DNA test.

Then, armed with genetic info, breeders could “breed away” from glaucoma-linked genes in their breeding programs, lessening the incidence of the disease over several generations.

“The ability to test puppies would enable breeders to identify which puppies should be kept in a breeding program versus their placement as pets,” explains Linda Kitzman, another Shiba Inu breeder. “As ambassadors to the breed, we should all do whatever we can to help end this painful, blinding disease.”

Miyadera has gratitude for the community that has supported the research.

“This work has largely been led by passionate breeders, and I’m hoping to grow the participation,” she says. “These breeders and owners are helping our understanding of the disease and the dogs that are at risk.”

“And something else is on the horizon that can benefit both dogs and people,” she adds, “is the possibility of developing tailored treatments that directly target the disease process of glaucoma.”

Every exam and every DNA sample brings the team one step closer to protecting vision in both dogs and humans.