Dorota Skowronska-Krawczyk watches a Greenland shark glide slowly through the dark waters of the Arctic on her computer screen.
“You see it move its eye,” says the University of California, Irvine associate professor of physiology and biophysics, pointing to the footage. “The shark is tracking the light — it’s fascinating.”
Greenland sharks are the longest-living vertebrates known to science, with some individuals surviving for as long as 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 in which the sharks live, scientists have long suspected that Greenland sharks may be functionally blind.
New research led by Skowronska-Krawczyk, however, suggests a very different picture.
Greenland Shark 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, is challenging assumptions about Greenland shark vision while offering new clues about aging and longevity.
Published in Nature Communications, the findings suggest that a DNA repair mechanism may allow Greenland sharks to preserve their eyesight for centuries without showing signs of retinal degeneration. Their visual systems also appear specially 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. Her interest in Greenland sharks began after reading a 2016 research paper by John Fleng Steffensen published in the journal Science.
“One of my takeaway conclusions from the Science paper was that many Greenland sharks have parasites attached to their eyes — which could impair their vision,” she says. “Evolutionarily speaking, you don’t keep the organ that you don’t need. After watching many videos, I realized this animal is moving its eyeball toward the light.”
That observation prompted her to investigate the sharks’ visual system more closely.
Studying Eyes From Centuries-Old Sharks
The Greenland sharks examined in the study were caught between 2020 and 2024 with scientific long lines 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 later be studied.
Emily Tom, a UC Irvine Ph.D. student and physician-scientist in training in Skowronska-Krawczyk’s laboratory, remembers the moment one of those preserved eyes arrived.
“I opened the package, and there was a giant, 200-year-old eyeball sitting on dry ice just staring back 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 up to a baseball-sized eyeball. Luckily, Dorota is very hands-on, both in her mentoring style and in the lab — which you don’t see a lot of with professors.”
Tom allowed the eye to defrost carefully.
“The lab smelled like a fish market,” she says.
Handling the tissue required precision. If it warmed too much and reached room temperature, the samples could begin to deteriorate.
No Signs of Retinal Cell Death
Tom performed histological and vision-specific analyses of the eye tissue. The researchers found no evidence of cell death in the retina.
They also discovered that rhodopsin (a protein essential for vision in dim light) remained active in the shark retina. The protein was tuned to detect blue light, an adaptation that could help Greenland sharks see in the faint light available deep beneath Arctic waters.
“Not a lot of people are working on sharks, especially shark vision,” Tom says. “We can learn so much about vision and longevity from long-lived species like the Greenland shark, so having the funds to do research like this is very important.”
The results suggest that the Greenland shark’s remarkable lifespan does not necessarily come with 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 shark eyes remain healthy for centuries could eventually point researchers toward new strategies for preventing 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 over extremely long periods and whether some of those protective mechanisms could ultimately be applied to humans.
Skowronska-Krawczyk says uncertainty surrounding 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 work is that we are the first in the world to see results — at the forefront, finding new mechanisms, rules and discoveries,” Skowronska-Krawczyk says, looking over at the paused shark on the screen. “Then, being able to share this joy with students — that’s the best part of it.”
