Mechanism

Mechanism

Choroid dissected from a calf's eye, tapetum lucidum appearing iridescent blue

The tapetum lucidum, which is iridescent, reflects light roughly on the interference principles of thin-film optics, as seen in other iridescent tissues. However, the tapetum lucidum cells are leucophores, not iridophores.

The tapetum lucidum is a retroreflector of the transparent sphere type. Because it is a retroreflector, it reflects light directly back along the light path. This serves to match the original and reflected light, thus maintaining the sharpness and contrast of the image on the retina. The tapetum lucidum reflects with constructive interference,^[3] thus increasing the quantity of light passing through the retina. In the cat, the tapetum lucidum lowers the minimum threshold of vision 6-fold, allowing the cat to see light that is invisible to human eyes.