May 16

Eyeshine from a doctors point of view

A listener writes “Wes, after listening to the “light” podcast I wanted to share some observations from an eye doctors point of view.

Timothy mentioned the light was white until he shined a green laser at them and then it turned red. What I think is happening is that the creature was unaware they were there or was looking in another direction. When the laser was shined in their eyes, Timothy mentions a “f stop like camera change”. This sounds like their pupils constricting. After that point the reflex is red because I believe that NOW the creature is looking directly at them. It not that they are mad but they totally have your attention and they looking directly at them.

Here is my theory.

They have a tapetum lucidium that reflects about 50% of the red spectrum of light while looking eye to eye. In most creatures with a tapetum lucidium, 40-50% of light reflection is the norm. Humans only reflect about 10% of the red spectrum to give you a comparison. The thickness of the tapetum lucidium is greatest at the center of vision where their macula is and thins as it progresses from the direct center in the back of the eye to the sides of the eye. The other thing that changes from the center to the side of the eye is the rod/ cone composition.

Center vision has more cones for color reception. Peripheral vision has more rods for night vision. This might explain the change in colors. It totally changes based on the angle the light enters. It might also explain their swaying side to side to better use their peripheral vision to see at night. Pilot’s and the military are trained to use their side vision at night for just such a purpose.

My estimate (from pictures I have been given) is their pupils are twice the size of ours. That’s a huge potential for light going in their eyes at night. If the moon is emitting .1 lux ( .1 lumen /m2) and 50% is reflected, I believe that reflection could be observable . Imagine a 13mm mirror. Don’t you think you might see a reflection of it in the moonlight? The difference from a mirror and their eyes is their eyes collect light from multiple directions when their pupils are large at night. They eye is bowl shaped unlike a mirror. So I believe ambient moonlight might appear to glow. Timothy said the lights appeared like the brightness of a Christmas tree light(led) which on average emit approximately only 0.4 to 4.0 lumens. Compare this with a candle that emits 12.57 lumens. I entirely believe that is possible to see this from 200 yards of a candle can be detected for miles.

I am working on a model that might demonstrate this. I need your help. I need some good eyeshine, glow, or close up daytime eye pictures to totally work this out. Any help would be appreciated. You can thank Gumshoe for his help so far.

I had an eyeshine experience at age 13 myself from about 12 feet and that is why I am trying to figure this out. And yes, I wish I had never seen it….

Thanks for being there for us”

9 Responses to “Eyeshine from a doctors point of view”

  1. Cindy W

    Thank you so kindly for explaining the light to us. It totally makes sense and maybe that’s why some folks say the eyes glowed instead of eyeshine. My husband is a professional photographer and he has tried to explain eyeshine to me as well but I understood your explanation as well. Thank you again for posting.

  2. Wolf W

    Great information.
    The excellent night vision these animals possess is IMO the single biggest contributing factor in their ability to avoid human contact.

    The swaying explanation makes perfect sense. I also tend to think they sway to both load their muscles ready for rapid movement and in order to see better through leaves and branches (which would explain the swaying often seen during the day).

  3. Diana M

    Could the change of head position when they are swaying back and forth or trying to see better with their peripheral vision also account for the changing eye color during some encounters? Is there any type of structure or structures possible in the eye that could cause the light to be reflected back in different colors depending on which part of the eye the light hits?

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