Groundbreaking research into the eyes of the world’s longest-living vertebrate could pave the way for new therapies to combat glaucoma and age-related macular degeneration, according to a study published in Nature Communications.1
The research challenges long-held assumptions about the Greenland shark (Somniosus microcephalus) and reveals remarkable mechanisms for preserving retinal integrity over centuries. It was led by UC Irvine Associate Professor Dorota Skowronska-Krawczyk in collaboration with University of Basel researchers Walter Salzburger and Lily Fogg.
DEFYING EXPECTATIONS
Greenland sharks, which can live up to 400 years, inhabit the exceptionally dim Arctic deep sea at depths approaching 3,000 metres. Their eyes are frequently parasitised by copepods (Ommatokoita elongata), which attach to the cornea, leading scientists to long suspect these sharks were functionally blind.
However, the new research provides evidence that Greenland sharks retain functional vision despite extreme longevity, corneal parasitisation, and minimal light. “Evolutionarily speaking, you don’t keep the organ that you don’t need,” Assoc Prof Skowronska-Krawczyk explained. “After watching many videos, I realised this animal is moving its eyeball towards the light.”
PRESERVED RETINAL STRUCTURE
Researchers examined retinas from adult Greenland sharks estimated to be over a century old and found no obvious signs of retinal degeneration.
The implications are striking when compared to human ageing. “At published rates of age-related rod loss (approximately 0.2–0.6% per year), a human living to 400 years of age would be expected to lose over 50–90% of their rod photoreceptors,” the study noted.
A TUNEL assay revealed no DNA fragmentation in the retinal sections, suggesting no ongoing DNA damage and cell death within the retina.
DNA REPAIR MECHANISMS
The key to preservation appears to lie in robust DNA repair mechanisms. Researchers found that the Greenland shark exhibits elevated expression of ERCC4 (XPF) compared to other sharks. The ERCC1-XPF DNA repair complex is known to play an important role in supporting retinal health and has been linked to retinal ageing across a range of species.
In humans, mutations in the ERCC1-XPF complex cause xeroderma pigmentosum, a progeroid syndrome characterised by UV sensitivity and early-onset vision loss. Similarly, ERCC1 knockout mice exhibit accelerated retinal degeneration, highlighting the complex’s role in protecting ocular tissues.
“The preferential retention and elevated expression of DNA repair genes linked to retinal degeneration suggests a potential mechanism underpinning their long retinal health span,” the study authors wrote.
ADAPTATIONS FOR SCOTOPIC VISION
The research also revealed that Greenland sharks possess a pure-rod retina with densely packed, elongated rods and comparatively thin inner retinal layers. Spectroscopic analysis of purified rhodopsin revealed a maximum absorbance wavelength of 458 nm, extremely blue-shifted even compared to other deep-sea species, reflecting adaptation to the highly transparent, blue-dominated light environments of deep Arctic waters.
Emily Tom, a UC Irvine PhD student who worked on the study, conducted histological analyses and found that rhodopsin in the shark retinas remains active and is tuned to detect blue light, with no signs of cell death.
Interestingly, corneal transmission measurements revealed that despite chronic parasitism, Greenland shark corneas ranged from 70 to 100% transmittance (compared to 95% in human corneas), allowing adequate light to reach the retina.
CLINICAL IMPLICATIONS
For Assoc Prof Skowronska-Krawczyk, who gleans insights into the molecular mechanisms of ageing by studying processes that control age-related eye diseases, the findings open significant possibilities. “The findings open the door to discovering new approaches to avoiding age-related vision loss and eradicating eye diseases such as macular degeneration and glaucoma,” she said.
“Not a lot of people are working on sharks, especially shark vision,” Ms Tom observed. “We can learn so much about vision and longevity from long-lived species like the Greenland shark.”
Reference
1. Rebolledo, C. Eye-Opening Research. UC Irvine News Jan 2026. Available at news.uci.edu/2026/01/05/eye-openingresearch [accessed Jan 2026].