Why do domestic cat eyes reflect light?

The domestic cat has a tendency to be more active at night although they are not wholly nocturnal. They are described as crepuscular, meaning active at dawn and dusk when hunting is more successful. In general, when possible they tend to be active when it is dark and for this reason evolution has been kind to them. It is given them a reflective layer behind the retina of their eyes which is called a photoreceptor and the Latin, scientific term is Tapetum lucidum.

The light reflecting cat eye
The light reflecting cat eye. Image: PoC.
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Its purpose is to contribute to better quality nightvision by reflecting the light received by the eye back onto the retina. The retina gets two goes at receiving the light before passing a signal via the optic nerve to the brain. Apparently, the Tapetum lucidum slightly blurs the image but no doubt this is a reasonable trade-off.

For the domestic cat and other cats it increases the sensitivity of the eyes by 44%. This is almost a 150% improvement in nightvision for the domestic cat over other species such as the human. Nearly imperceptible objects for humans become visible to cats. Of course, humans do not have this reflective layer behind their eyes. This is because as a species we are active during the daytime.

Reflecting eyes
Source: Tapetum lucidum

This specialist photoreceptor is iridescent and its tissues are leucophores. In tigers the colour of the tapetum lucidum is greenish. Night-time photographs with directed light (e.g. a torch) or flash photography of domestic cats indicates that the colour of their Tapetum lucidum varies between hues of yellow, green and even cyan/blue. Although often the reflection is so bright that the colour is burnt out to a white.

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