Why do cats’ eyes shine? Science answers

A scientific curiosity that seems to have an answer.

Surely on some occasion we have seen a cat at night or in the dark, highlighting the brightness of their eyes especially when some kind of light focuses on them.

Although it is something that is not strange to us, it is probable that in some occasion we have asked ourselves the reason of this brightness.What is it about their eyes that makes them shine in this way and if it is of any use to them. In this article we intend to give an answer to this question.

In fact, this is a question that has aroused man's curiosity since ancient times, cats being considered the guardians of the night and of the underworld in ancient Egypt, among other aspects, due to this particularity. It was believed that the iridescence of their eyes at night was due to the fact that they saw the truth and even beyond death, and that it kept the sunlight in the world. But the brightness of a cat's eyes has a scientific explanation, the tapetum lucidum.

Why do cats' eyes shine? The tapetum lucidum

The answer to why cats' eyes shine is none other than the existence of a band of cells located behind the photoreceptors in the eyes of these animals, specifically between the retina and the optic nerve (it could be considered part of the choroid). Called the tapetum lucidum, it acts as a concave mirror inside the eye, causing light entering through the pupil to pass through the retina both as it enters the eye and as it bounces off the tapetum lucidum. Thus, the amount of light reflected on the retina is greatly increased, and can even be perceived from the outside.. Technically, it is not that their eyes shine, but that they reflect the external light.

This means that they are able to capture and make the most of the ambient light, so that during the night they are able to move more easily than other creatures and can see in the dark as long as it is not total darkness. Their visual capacity is greatly increased and serves as a deterrent to possible attacks.

The tapetum lucidum increases the sensitivity of the rods thirty to fifty times, although this would not be enough to allow them to see in total darkness. In most animals without this adaptation, much of the visual information is lost because the eye does not reflect all the light entering through the pupil. In the case of cats, although there is some loss of information, this loss is much less due to the presence of the tapetum lucidum.This causes a much higher proportion of light to be retained in the retina and the rods in the eyes can process much more information.

Not only cats

The tapetum lucidum is what causes cats' eyes to glow in the dark, but it is a Biological adaptation shared with other species. Cats are not the only creatures whose eyes glow at night. We can observe the same effect in most feline species and even in most canines. Bats, sharks, horses, crocodiles or even cows also have tapetum lucidum.

In general, these animals have nocturnal habits, both in terms of predators and prey. Evolution has generated the emergence of structures of this type so that those beings that live and act mainly at night or whose prey or predators have such habits can survive. However, mainly diurnal animals do not usually possess it, such as humans and pigs.

Can it cause difficulties for them?

Tapetum lucidum has many advantages, but one might think that it can be a disadvantage in situations where there is a lot of light, such as during the day. However, the vision of cats has other characteristics that allow them to adapt to other difficulties..

Among them they have a pupil capable of contracting to unsuspected limits, contracting to a narrow strip and managing to reduce the amount of light entering the eyes when it is intense.

Bibliographical references:

• Coles, J.A. (1971). Some reflective properties of the tapetum lucidum of the cat's eye J.Physiol.; 212(2): 393-409.