Happy Holidays! I hope you all had a wonderful Holiday Season and 2024 is treating you well so far! Now come down the rabbit hole with me that is Tapetum Lucidum!
First off, before I get into what the heck Tapetum Lucidum is, I must address the above photo of our beloved Fran: it is so strange. I love it. I placed two glowing golf balls by his fur to see what it would look like (and you can see the colors on his fur are super cute and Christmas-y) but what I did not expect to happen was the light bouncing off his eyes, making them glow! He looks like a cyborg. And at the time I had no idea why the light reflected into opposite eyes the way it does, but I did a little research and found that:
"Cats and dogs with a blue eye color may display both eyeshine and red-eye effect."
Now, you may find yourself wondering, "So what exactly does that mean?"
Well, many animals, bugs, and fish have a little something that humans don't called Tapetum Lucidum, which is "a layer of tissue in the eye... lying immediately behind the retina, it is a retroreflector. It reflects visible light back through the retina, increasing the light available to the photoreceptors... {It} contributes to the superior night vision in some animals."
Ah, science. How fun it is to dissect what the heck all that means.
Humans do not have Tapetum Lucidum. Cats do. Hence, we have found ourselves back to Franklin and the strange picture featured above. Basically what all of these science quotes mean is that, because of this extra layer in Franklin's eye that is there for his nocturnal vision, the light from the golfballs caused the green and red-eye glowing effect. Yes, the golfballs themselves are green and red, but it is the glow, the cyborg-like appearance, that is from the extra layer in Franklin's eyeballs. The green eye is from eyeshine found in blue-eyed animals, and the red-eye is from the red-eye effect of eyeshine (which is much more common amongst animals).
Eyeshine can come in many different colors, depending on the animal and the color of the iris. It is the visible glowing effect when a lot of light shines into an animal's eye and is reflected back. In blue-eyed animals, as stated above, each eye may reflect the two different colors of red and green at the same time. In Tiger's, with their yellow eyes, the eyeshine in both appears green, while in horses the eyeshine in both appears blue.
If you would like to read more about Tapetum Lucidum, I have linked the Wikipedia article here. Now of course, as we all know, Wikipedia is not the most factual source on the web, but it is commonly the easiest for us non-scientists like myself to understand. With a little more digital digging I found these articles as well, should you want to continue down the rabbit hole with more official science lingo and terms:
Science Direct: Tapetum Lucidum
National Library of Medicine: Comparative Morphology of the Tapetum Lucidum (among selected species)
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