Ok, have a look at this shot...particularly the eyes of the SEO. They look weird, right? It took me a little while to figure out why. You might pick up on this faster than I did. => The pupils are different sizes. That is very cool - something I didn't realize would happen when one eye is in the sun and the other is in shadow. Never thought about that. Here's the shot (very quick edit):
A very cool shot. I have tried and tried to find out info about the different pupil sizes that I have seen in owls. There were some burrowing owl shots awhile back that showed this as well and that started me on my veterinary ophthalmology quest. As most of you know our pupils are supposed to be equal and respond equally to light. So even if one eye is totally covered it will respond and remain at an equal size to an eye that is in bright light...why? Nerve fibers from each optic nerve meet at the optic chiasm and then fibers from each eye pass to both sides of the brain. So, light shined into one eye elicits a response in both.
I guess I need to do more research
Eric
It does happen to people, when they get a hard hit on the head. In fact it's a diagnostic sign that says, "Concussion." Hope it's not as serious in owls!
Mark
So, here's the skinny on owls' eyes/pupils. This is totally normal as owls can independently control their pupil size...therefore the pupil in the dark will be larger than the one in the light. The muscle fibers of the iris in humans is very different than birds/owls. People have irides made of smooth muscle and owls striated muscle. What's the advantage...striated muscle (like the muscle in your legs, arms) responds much quicker and allows these birds to quickly change their iris size when going from light to dark, (bright sun to shadow or darkness in a forest for example).
Mark, you are correct that abnormal pupil size can certainly be a sign of head trauma but in these birds it's just an evolutionary advantage...isn't nature amazing!
Eric
Here is a pretty good illustration. The owl on the left has two different size pupils and you can see that light is hitting each eye a bit differently. The left eye, with more light, has a smaller pupil and the right a bit larger...certainly not as exaggerated as in the SEO but pretty clearly different. Its sibling which sits in the shade has equal pupils related to equal amount of light delivered to each eye.
Eric http://eyelaser.smugmug.com/Nature/Owls/i-dqhPh4F/0/XL/4A9C0947-EditMom3chicks-XL.jpg
eyelaser wrote:
Here is a pretty good illustration. The owl on the left has two different size pupils and you can see that light is hitting each eye a bit differently. The left eye, with more light, has a smaller pupil and the right a bit larger...certainly not as exaggerated as in the SEO but pretty clearly different. Its sibling which sits in the shade has equal pupils related to equal amount of light delivered to each eye.
Eric http://eyelaser.smugmug.com/Nature/Owls/i-dqhPh4F/0/XL/4A9C0947-EditMom3chicks-XL.jpg
