When light catches an animal’s eyes in the dark, “eye shine” occurs. This reflection appears as eerie, glowing dots in low-light. It’s a natural biological process resulting from a specialized eye structure. This effect allows many animal species to navigate their environment after dusk.
How Animal Eyes Glow
Eye shine is scientifically explained by the tapetum lucidum, a reflective layer behind the retina in many animals. This term translates from Latin as “bright tapestry” or “shining tapestry,” describing its mirror-like function. When light enters an eye with a tapetum lucidum, it first passes through the retina; light not absorbed by photoreceptor cells then strikes this layer, which reflects it back through the retina, giving photoreceptor cells a second chance to absorb photons. This “double pass” significantly increases eye sensitivity, enhancing vision in dim conditions. Eye shine color, ranging from white, blue, yellow, green, to red, varies by animal species, observation angle, and the reflective crystals’ composition.
Animals with Green Night Eyes
Many animals exhibit a distinct green eye shine at night, often seen in Order Carnivora members.
- Domestic cats often display yellow-green or yellow-orange eyeshine, due to riboflavin and zinc in their tapetum lucidum. However, blue-eyed breeds like Siamese sometimes lack a tapetum lucidum.
- Raccoons commonly show bright yellow or yellow-green eyeshine, indicating a high concentration of light-sensitive rods.
- Certain dog breeds also exhibit green eye shine, though the hue varies. Their tapetum lucidum contains zinc-rich rodlets contributing to this coloration; puppies may display blue eyeshine before their eyes fully mature.
- Foxes typically have green eyeshine, though it can also appear orange to red.
- Some amphibians like bullfrogs can have eyes that appear greenish in the dark.
- Tigers also have a greenish tapetum lucidum.
The Purpose of Eye Shine
The tapetum lucidum provides a significant evolutionary advantage for animals, particularly those active during twilight or nocturnal hours. This adaptation greatly improves an animal’s ability to see in low-light, allowing effective use of scarce light sources like moonlight or starlight. For nocturnal predators, this enhanced vision is instrumental in locating and hunting prey; for prey animals, improved night vision allows them to detect threats, providing a better chance to evade danger. This mechanism enables animals to navigate, forage, and move safely through their environment when light is limited. The tapetum lucidum can enhance visual sensitivity by as much as 50 percent, or up to six times better than human vision in some species like cats.