Dorota Skowronska-Krawczyk watches on her computer screen as a Greenland shark slowly glides through the dark waters of the Arctic.
“You can see how the eye moves,” says the associate professor of physiology and biophysics at the University of California, Irvine, pointing to the images. “The shark follows the light; it’s fascinating.”
Greenland sharks are the longest-lived vertebrates known to science, with some individuals surviving up to 400 years. They have thick gray bodies, small heads, and short, rounded snouts. Their cloudy-looking eyes can appear almost lifeless, and parasites are often found attached directly to the eyeballs.
Because of those parasites and the extremely dark, murky environment the sharks live in, scientists have long suspected that Greenland sharks may be functionally blind.
However, new research led by Skowronska-Krawczyk suggests a very different picture.
Greenland shark’s eyes defy expectations
The study, co-authored by researchers from the University of Basel, Switzerland, Walter Salzburger and Lily G. Fogg, who examined the evolutionary aspects of the work, challenges assumptions about the vision of Greenland sharks while offering new clues about aging and longevity.
Published in Nature CommunicationsThe findings suggest that a DNA repair mechanism could allow Greenland sharks to preserve their sight for centuries without showing signs of retinal degeneration. Their visual systems also seem uniquely adapted to the extremely low light levels of their arctic habitat.
Skowronska-Krawczyk studies the molecular processes involved in age-related eye diseases to better understand how aging affects vision. His interest in Greenland sharks began after reading a Research work from 2016. by John Fleng Steffensen published in the magazine Science.
“One of my conclusions from Science “The paper was that many Greenland sharks have parasites attached to their eyes, which could affect their vision,” he says. “Evolutionarily speaking, you don’t keep the organ you don’t need. After watching a lot of videos, I realized that this animal moves its eyeball toward the light.”
That observation prompted her to investigate the sharks’ visual system more closely.
Studying the eyes of centuries-old sharks
The Greenland sharks examined in the study were caught between 2020 and 2024 on scientific longlines near the University of Copenhagen’s Arctic Station on Disko Island, Greenland.
Steffensen, a professor of marine biology at the University of Copenhagen, worked with Peter G. Bushnell, who teaches at Indiana University South Bend, and Richard W. Brill of the Virginia Institute of Marine Science. The researchers dissected the sharks’ eyes and preserved them in a fixative solution so they could be studied later.
Emily Tom, Ph.D. from UC Irvine. student and doctor-scientist in training in the Skowronska-Krawczyk laboratory, remembers the moment when one of those preserved eyes arrived.
“I opened the package and there was a giant 200-year-old eyeball sitting on dry ice staring at me,” the 28-year-old says with a laugh. “We’re used to working with mouse eyeballs, which are the size of a papaya seed, so we had to figure out how to scale it up to an eyeball the size of a baseball. Fortunately, Dorota is very hands-on, both in her tutoring style and in the lab, which is something you don’t see much with professors.”
Tom carefully let the eye thaw.
“The lab smelled like a fish market,” he says.
Handling the tissue required precision. If it got too hot and reached room temperature, the samples could start to deteriorate.
No signs of retinal cell death
Tom performed histological and vision-specific analyzes of ocular tissue. The researchers found no evidence of cell death in the retina.
They also found that rhodopsin (a protein essential for low-light vision) remained active in the shark’s retina. The protein was tuned to detect blue light, an adaptation that could help Greenland sharks see in the dim light available deep in Arctic waters.
“There aren’t many people working with sharks, especially with shark vision,” Tom says. “We can learn a lot about the vision and longevity of long-lived species like the Greenland shark, so having the funding to do research like this is very important.”
The results suggest that the Greenland shark’s remarkable lifespan is not necessarily accompanied by the severe retinal deterioration that might be expected in such an old animal.
What Greenland sharks could teach us about aging
For Skowronska-Krawczyk, the work raises the possibility that understanding how Greenland sharks’ eyes stay healthy for centuries could eventually point researchers toward new strategies to prevent age-related vision loss.
The findings could also help guide research into eye diseases, including macular degeneration and glaucoma. At the same time, they raise broader questions about how vision evolves, how tissues remain functional for extremely long periods, and whether some of those protective mechanisms could ultimately apply to humans.
Skowronska-Krawczyk says uncertainty around federal research funding has created concerns about future support for this type of work, but she remains confident that “we will prevail.”
“What I love about my job is that we are the first in the world to see results: we are at the forefront, finding new mechanisms, rules and discoveries,” says Skowronska-Krawczyk, looking at the shark stopped on the screen. “So, being able to share this joy with the students… that’s the best part.”