Groundbreaking Eye Surgery Performed on Wolverine at San Francisco Zoo

Edward, a 2-year-old wolverine at San Francisco Zoo & Gardens, is seeing better thanks to a first-ever novel lens corrective procedure on a wolverine’s eye. Following a recent cataract surgery, he became the first wolverine to have a custom-made intraocular lens implanted in his left eye. 

Born at Billings’ ZooMontana in 2023, Edward was transferred to San Francisco Zoo later that year. While wolverines are generally solitary predators in the wild, Edward now enjoys the company of his female companion, Molly. In May 2025, the 30-pound male wolverine’s caretakers noticed his right eye was cloudy and informed the Zoo’s veterinary team.

“We were surprised to see what appeared to be a cataract forming in the eye of such a young animal,” said Dr. Nick Dannemiller, clinical veterinarian at the Zoo and board-certified specialist in zoological medicine. “So, we called an ophthalmologist to further evaluate Edward’s condition.”

Dr. Kate Freeman is no stranger to treating exotic animals. The board-certified veterinary ophthalmologist holds a Master’s degree concentrating on marine conservation and ecology, and her focus in veterinary school was zoo/wildlife animals, with the initial intention of becoming a wildlife veterinarian. Beyond her practice at the nearby Veterinary Vision, she also works as a veterinarian at The Marine Mammal Center in Sausalito and routinely travels to a handful of animal facilities to care for the eyes of various exotic animals and wildlife.

Dr. Freeman officially diagnosed a mature cataract in Edward’s right eye in June and noticed a small cataract forming in his left eye. A successful surgery to remove the cataract in the right eye was performed in August.

“In a cataract surgery, the contents of the lens, that normally refract light to the retina, are removed because they have become clouded, obscuring vision,” said Dr. Freeman. “In humans, and even in cats and dogs, there are manufactured replacement lenses made specifically for those species. At the time of Edward’s first surgery, there were no artificial lenses made for a wolverine.”

Edward was left without a replacement lens, leaving him farsighted in his right eye – unable to see close up.

Realizing that Edward would eventually also need cataract surgery on his left eye, Dr. Freeman was determined to find a solution for him, knowing he would not do well being farsighted in both eyes. She turned to an old mentor, veterinary ophthalmologist Dr. Christopher Murphy, professor emeritus at the UC Davis School of Veterinary Medicine, where Dr. Freeman completed her comparative ophthalmology residency in 2012.

Dr. Murphy, in turn, called an old friend and colleague, (human medicine) optometrist Dr. Donald Mutti, professor at The Ohio State University College of Optometry.

“Dr. Murphy and I have worked together for many years calculating the intraocular lens measurements for various birds – a falcon and an eagle,” said Dr. Mutti. “I wasn’t about to pass on a wolverine case. Even though I’m a loyal Buckeye, I just couldn’t leave an innocent wolverine in the lurch,” continued Dr. Mutti, referencing the Ohio State and Michigan mascots and the heated rivalry between those two universities. “Everyone deserves good vision.”

That’s right, a Buckeye was about to help a wolverine!

“The amount of farsightedness in Edward’s eye without an implant would be extremely high,” said Dr. Mutti. “A high level of farsightedness in a person is about 10 diopters, units of optical power. My guess is that Edward was at about a level of 50 diopters, where he’d be able to see whether lights were on or off and maybe some gross motion, but there would be no capability for detail vision in Edward’s eye.”

The vision specialists got to work calculating the specific measurements for a custom-made lens for Edward. In clinic, Dr. Freeman and her colleague Dr. Maggie LiPuma performed high resolution ultrasound and corneal measurements using a keratometer on loan from Micro Medical Devices to determine corneal dimensions and curvature. Using all measurements, the vision specialists were able to analyze and calculate the corneal curvature, size of natural lens, length of the eye, and where the lens would sit following surgery. After many different calculations, and consultation with the lens manufacturer, an-vision, the team settled on an optical power of 100 diopters for Edward’s lens and had the lens created. In comparison, cats are 53.5 on the scale, and dogs are generally 41 diopters. The optical power for human lenses varies based on individual calculations.

“Based on the measurements we calculated, a dog or cat lens would not work well for a wolverine, so we elected to have a special one made for him,” said Dr. Freeman.

In November, Edward underwent a second cataract surgery, this time on his left eye. Dr. Freeman successfully implanted the custom-made lens into that eye. It was determined best to leave the right eye without a replacement lens as that eye was doing very well, and wolverine eyes are sensitive to procedures.

“Every time you open up an eye, you introduce potential problems,” said Dr. Freeman, explaining why a lens was not placed in his right eye also. “Since we knew Edward was doing well with only one eye farsighted, it was best to leave the right eye aphakic (without a lens).”

The world’s first wolverine to have a corrective intraocular lens implanted in his eye is doing much better according to his care team.

“Before the first surgery, he was very mistrusting of doing anything on the right side of his body,” said Dr. Dannemiller, about evaluating Edward’s vision. “After the surgery, we believe he can see a bit better, albeit aphakic, because he was more willing to present his right side during training activities. And now after the second surgery, we notice improvements in his overall vision.”

Edward now receives eye drops two to three times a day. Thanks to exceptional training by his handlers, he voluntarily receives the drops.

Edward’s improved vision was noticed recently when he successfully out-hunted Molly to catch a small rodent that naturally appeared in his exhibit, so his care team is encouraged by the success of the surgery.

While Edward eats a wolverine’s natural carnivore diet (rabbits, poultry, etc.), the random rodent was an anomaly – he does not have to hunt for his food normally. He does, however, enjoy one peculiarity in his diet – he is quite fond of taco seasoning.

“He can’t get enough of it,” said Dr. Dannemiller. “He loves taco seasoning on everything. Even if you sprinkle a little in his habitat, he will tear through the exhibit trying to find it.”

Going forward, Dr. Freeman and the Zoo will continue to monitor Edward’s vision and expect him to live a normal life.

Dr. Dannemiller approximates that wolverines typically live 5-10 years in the wild and up to 15-20 years under human care. Currently, there are only about 30 wolverines at zoos and wildlife centers in North America. Wolverines are listed as a threatened species under the Endangered Species Act, primarily due to climate change and habitat loss, with an estimated 300 individuals remaining in the contiguous United States.

As for this Saturday’s Ohio State-Michigan football game, we presume Edward will be rooting for the Michigan Wolverines, but he may now have a soft spot for the Buckeyes after receiving their help.

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Media Resources

Media Contacts:

• Dr. Kate Freeman, Veterinary Vision, ktsfreeman@gmail.com
• Nancy Chan, San Francisco Zoo, nancychan@sfzoo.org
• Dr. Donald Mutti, The Ohio State University, mutti.2@osu.edu 

Press kit:

Downloadable photos and videos of Edwards’ eyes, examinations, and surgery