Greenland Sharks May Not Be Blind After All, Study Finds Age-Defying Eyes

New research led by Dorota Skowronska-Krawczyk, a University of California, Irvine associate professor of physiology and biophysics, challenges the long-held assumption that Greenland sharks are functionally blind. The study, published in Nature Communications, was co-authored by Walter Salzburger and Lily G. Fogg of the University of Basel in Switzerland, who examined the evolutionary aspects of the work.

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, and their cloudy-looking eyes often have parasites attached directly to the eyeballs. Because of those parasites and the extremely dark, murky environment the sharks inhabit, scientists have long suspected Greenland sharks may be functionally blind.

The sharks examined in the study were caught between 2020 and 2024 using scientific long lines near the University of Copenhagen's Arctic Station on Disko Island, Greenland, by John Fleng Steffensen, a professor of marine biology at the University of Copenhagen, working with Peter G. Bushnell of 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 for study. At UC Irvine, PhD student Emily Tom performed histological and vision-specific analyses; the team had to adapt techniques usually used on mouse eyeballs, which are about the size of a papaya seed, to work with the sharks' baseball-sized eyes.

The researchers found no evidence of cell death in the retina, and they 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.

The findings suggest that a DNA repair mechanism may allow Greenland sharks to preserve their eyesight for centuries without the severe retinal deterioration that might be expected in such an old animal. The results could also help guide research into age-related eye diseases including macular degeneration and glaucoma.