Nature 2026 study finds bird inner retinas run entirely on anaerobic glycolysis with zero oxygen, resolving a centuries-old paradox in vertebrate physiology.
Key Takeaways
Microsensor measurements in zebra finches, pigeons, and chickens confirmed the inner retina operates in chronic anoxia; outer retina retains some blood vessels and aerobic respiration.
Spatial transcriptomics showed anaerobic glycolysis genes active in the avascular inner retina; the pecten oculi pumps glucose in and exports lactic acid out rather than delivering oxygen.
The inner retina consumes 2.5x more glucose than other bird brain regions, making it the most energetically demanding known vertebrate tissue running without oxygen.
Evolutionary timeline places the adaptation after the avian split from crocodilians but before modern birds, likely in theropod dinosaurs; reptile relatives show normal retinal oxygen levels.
Removing blood vessels may improve visual resolution by eliminating occlusion; this could also explain maintained retinal function during high-altitude, low-oxygen flight.
