Greenland shark's 400-year vision offers clues to fighting age-related blindness

For decades, marine biologists assumed the Greenland shark was essentially sightless. These massive creatures drift through the perpetual darkness of Arctic waters, their eyes often clouded and scarred by parasites that attach to the cornea. The assumption seemed reasonable: a blind fish in a lightless sea. But a team at UC Irvine has overturned that logic entirely, and in doing so, stumbled onto something that might matter far more than shark biology.

Dorota Skowronska-Krawczyk, an associate professor at the university, was reviewing video footage of a Greenland shark moving through the black water when she noticed something that shouldn't have been there. The shark's eye was tracking the light. Not passively drifting, but actively following it—the kind of deliberate movement you'd expect from an animal that could actually see. That single observation was enough to make her question everything the field had accepted as fact.

Greenland sharks hold a singular place in vertebrate biology. They are the longest-living animals of their kind that science has documented, with some individuals reaching 400 years old. Their bodies are thick and grey, their heads small, their snouts rounded. But it's the eyes that have always puzzled researchers. Many appear milky and inert, often with a parasitic copepod hanging from the surface. Combined with the absolute darkness of their habitat, the conclusion seemed inescapable: these sharks had lost their sight long ago.

Obtaining tissue samples from a Greenland shark is not a simple matter. Between 2020 and 2024, researchers collected specimens near Disko Island in Greenland and preserved the eyes for transport to Skowronska-Krawczyk's laboratory. When Emily Tom, a PhD student and physician scientist in training, opened the package containing two eyes estimated at roughly 100 years old each, she was confronted with something she had never encountered before—eyeballs the size of baseballs, preserved and waiting for examination.

What Tom found under the microscope contradicted the prevailing assumption entirely. Using histological analysis, she detected no evidence of cell death in the retina. More striking still was the presence of rhodopsin, a protein critical for vision in low-light conditions, and it was not merely present—it was fully functional. The protein had evolved to be sensitive specifically to blue light, the wavelength that penetrates furthest through water. The shark's eye, it seemed, had been engineered by evolution to see in exactly the environment it inhabited.

The research, published in Nature Communications and conducted in collaboration with evolutionary biologists at the University of Basel, points to a DNA repair mechanism operating within the shark's retina. This mechanism appears to shield the tissue from the cumulative damage that typically accumulates with age. In humans, the eye is often the first system to show signs of aging, manifesting as macular degeneration, glaucoma, and other vision disorders. If a creature that lives for four centuries can maintain retinal integrity across that span, the mechanisms responsible might offer a template for protecting human vision as people grow older.

Skowronska-Krawczyk sees the implications extending well beyond shark biology. Long-lived animals represent a kind of natural experiment in cellular resilience, a chance to observe how tissues resist the ravages of time across timescales that laboratory studies cannot replicate. Few researchers have focused on shark vision specifically, which makes this discovery particularly valuable. The slow-moving predator of the Arctic deep, with its cloudy eyes and parasitic passengers, may yet become a teacher in the fight against blindness.