File:Corgi With Heterochromatic Eyeshine.jpg

English: I first noticed my dog’s eyes' differing reflections last year by accident. I was trying to take a photo of him in the dark, but my flash was turned on. I did some research, and I found that the reason his eyes reflect different colors is because of thin-film interference. Some animals have a thin layer of cells behind their retina called the tapetum lucidum. These cells form a reflective crystalline structure that produces thin-film interference. Thin-film interference is caused when outer and inner layers of a thin film both reflect light, causing it to interfere either constructively or destructively due to the fact that light exhibits wave-like properties. The tapetum lucidum uses constructive interference to amplify the light it receives and send it back to the photoreceptors of the eye. This helps the animal see better in low light, and causes the pupil to glow somewhat. The reason that my dog’s eyes reflect different colors is because the brown eye has a tapetum lucidum, which reflects a greenish color in this case, but blue eyes in dogs typically do not, and therefore do not reflect light as prominently. The reason for the red reflection in the blue eye is the reflection of red light by the blood vessels in the eye. This red shine is typically referred to as “red eye”, which is present in humans too. When I first noticed this quirk of my dog I had no idea how complicated and interesting the physics behind it were. This process taught me that nature can find wildly complex solutions to problems through the process of evolution.