Is Century-Long Biological Health Possible? Lessons from the Greenland Shark

(Posted on Thursday, January 15, 2026)

Can living organisms truly maintain themselves, down to their most delicate tissues, for centuries? This question, once the realm of speculation, finds a striking example in the Greenland shark. The eyes of these 400-year-old sharks provide insight into preserving vision over a lifetime. A recent study shows that the Greenland shark, the longest-living vertebrate, maintains an intact and functional visual system despite advanced age, low light, cold water and chronic eye parasites.

These sharks inhabit Arctic waters, where their eyes frequently host small parasites once believed to cause near blindness. However, both the eyes and the associated nerves remain healthy for more than a century, showing none of the age-related vision problems common in humans. Investigating these mechanisms may inform future strategies to maintain human vision with age.

How Greenland Sharks Defy Vision Loss

Prior to this research, the Greenland shark was recognized primarily for its exceptional lifespan, which can reach 400 years. Living in deep, cold Arctic waters, it often carries parasites, called copepods, which can sometimes cover a large part of the cornea. This makes the eye appear cloudy or even gives the shark a ghostly look. Despite this, the shark’s visual adaptations allow it to see well enough to navigate and hunt in the dark, deep sea, even when much of the eye is covered.

Research found that the shark’s eyes contain rod cells—specialized cells highly sensitive to dim light—which allow it to see in the deep ocean where sunlight is scarce. The eye also has a mirror-like layer, called the tapetum lucidum, that reflects light back through the retina. This increases the chances of detecting faint light.

While the shark cannot see colors or fine details, it is extremely good at detecting small movements and shapes in near-total darkness. Tests revealed that the shark’s vision is most sensitive to blue wavelengths, which are the most common light in deep ocean waters.

Another key finding is that the Greenland shark’s eyes do not exhibit the cellular degeneration typical of aging human eyes. Sharks over 130 years old show no evidence of cell loss or other age-related visual decline. The eyes possess robust cellular repair mechanisms, which likely contribute to their sustained function over the course of centuries.

What Shark Eyes Teach Us About Preserving Human Vision

The Greenland shark’s ability to preserve retinal neurons for centuries is significant, as human retinal diseases such as age-related macular degeneration and inherited degenerations result from progressive, unrepaired damage. Identifying the biological strategies that support long-term neural health in the shark’s retina may inform new approaches to protect human vision.

The Greenland shark demonstrates that eyes can maintain function for extended periods, even in challenging environments. This finding challenges the assumption that visual decline is inevitable with age. It’s important to note that the study’s scope is limited by the small sample size and the difficulty of accurately determining shark ages. It also did not assess visual performance in natural settings. Despite these limitations, available evidence indicates that Greenland shark eyes remain healthy for exceptionally long periods.

Studying the shark’s cellular repair processes may reveal methods to enhance human ocular health and disease resilience. These themes are also explored in the book Better Eyesight: What You and Modern Medicine Can Do to Improve Your Vision, which discusses the latest advances in eye care, including new treatments and technologies that support lifelong healthy vision.

The Future: Can Human Eyes Match The Shark’s Longevity?

The Greenland shark’s eyes force us to rethink what is possible when it comes to vision and aging. If a living system can maintain itself for centuries—like the eyes of this shark—should this be the goal of regenerative medicine for humans? Science still needs to find out exactly how the shark’s eyes repair themselves and whether other long-lived animals do the same. As we learn more, we might be able to focus on preventing human eye diseases before they start, rather than just treating them. While these discoveries are just beginning, the Greenland shark offers hope that a lifetime of healthy vision could become a reality—and invites us to consider whether our own biology might one day match this extraordinary feat.