A 400-year-old eye that still tracks light
Dorota Skowronska-Krawczyk, an associate professor of physiology and biophysics at the University of California, Irvine, points to footage of a Greenland shark gliding through Arctic waters. "You see it move its eye," she says. "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.
Challenging assumptions about shark vision
The study, co-authored by Walter Salzburger and Lily G. Fogg from the University of Basel, Switzerland, who examined the evolutionary aspects of the work, challenges 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."
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. The researchers who dissected the sharks' eyes included Steffensen, Peter G. Bushnell, and Richard W. Brill.
Emily Tom, a 28-year-old UC Irvine Ph.D. student, described a preserved Greenland shark eye as "a giant, 200-year-old eyeball sitting on dry ice just staring back at me."
A retina that doesn't age
The researchers found no evidence of cell death in the Greenland shark retina. Rhodopsin, the light-sensitive protein in rod cells, remained active in the retina and was tuned to detect blue light, an adaptation suited to the dim, blue-shifted light of the deep Arctic waters.
These findings could help guide research into eye diseases including macular degeneration and glaucoma, which are often linked to retinal degeneration.
Skowronska-Krawczyk expressed concerns about future support for this type of work due to uncertainty surrounding federal research funding, but she remains confident that "we will prevail." She added, "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."