When light falls across an animal at night, the eerie glow that peers back at you from the dark can be disconcerting.
The very reason that animals produce this glow and people do not is what allows them to see so well in the dark. This eye-shine is made of light reflected back from a layer of cells that lie below the retina at the back of the eye.
In horses and other animals, this layer of cells is called the tapetum. It covers the upper half of the ocular fundis, which is the back curvature of the inner eye. It gives the light a second chance to hit the cones and rods that it missed in its first pass across the retina. This increased light exposure is the key to low light vision.
The next time you see eyes shining in the dark, from a pet, a horse, or wild animal; just remember that you’re seeing light reflected from a single layer of cells.
Watch a video of a horse eye exam here.