Ever wonder why Kitty’s eyes gleam in photographs? It turns out that many mammalian species that need to see well in the dark—like dogs, cats, deer, and cows—have a shiny, reflective surface on the top part of their retina called the tapetum lucidum, which is Latin for “bright tapestry.” The reason for this name? Well, you guessed it—because people noticed that these animals’ eyes gleamed green, blue, yellow, or red. (My favorite photo of my chocolate Labrador is one with her eyes flashing bright red as she demonically plays with her stuffed Dudley the Dinosaur.) The tapetum lucidum sits just behind the retina, and reflects light back into the retina, which really improves night vision.
A few weeks ago, I was able to see the tapetum lucidum in a whole new way, using an ophthalmoscope for the first time. An ophthalmoscope is basically a combined light source and set of magnifying glasses. Because this was our first time using it to examine the eye, we started off with the basics: shutting off the lights, turning on the ophthalmoscope, then finding the eye, which you spot as an explosion of bright color caused by our friend the tapetum lucidum. I was blown away by how colorful our teaching Beagle’s tapetum was—swirls of yellow and green on a base of bright orange, so bright and cheerful it reminded me of lighting up a Christmas tree in the middle of winter.
Once you spot the tapetum lucidum, you bring yourself (and the ophthalmoscope) closer, changing magnification as needed as you look at different structures of the eye. I had a very hard time seeing anything other than the tapetum, but I realized it was because I was focusing on the top part of the retina; if I wanted to see anything else, like blood vessels or the optic nerve, I’d have to angle downward and examine the bottom part of the retina. I think I saw some blurry blood vessels, but honestly I thought I was doing just fine for my first time using an ophthalmoscope and working with an overly affectionate Beagle!