|MadSci Network: Biochemistry|
My last dog had eyes that always glowed red in the dark. My new dog's eyes glow green. Why should this be so?
Animals which spend part of their time using their eyes in dim light (or whose ancestors did so) have reflective retinas. You see, not all light is absorbed by visual pigments in the retina; some of it passes through. A mirrored layer called the tapetum lucidum, behind the retina, reflects some of this light back through the retina so it has more chance of being captured. The animal loses some visual acuity this way, but makes more efficient use of low light.
As to why your two dogs have eyes that glow different colors, I have no real clue. Are their irises different colors? It is also possible that one of them has visual pigments which absorb shorter wavelengths (so the non-absorbed light would look red) than the other.
Information in this answer was cribbed from this article in Outside magazine.
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