Why do cats’ eyes glow GREEN?

Well, the truth of the matter is that domestic cats’ eyes don’t only glow green in the dark. You will see a range of colours from green, yellow-green (cyan), orange and a reddish colour. We know the reason why domestic cats have glow-in-the-dark eyes. It’s because there’s a reflective layer behind the retina of each eye. When light enters the eye at 90° or perpendicular to the retina it is reflected straight back out of the eye via the lens and cornea and the reflected light takes on the colour of both the reflective layer which is called the tapetum lucidum and the retina. So, what you’re seeing in those colours is the colour of these parts of the domestic cat’s eye anatomy.

The indication is, that the tapetum lucidum is a yellow/green colour. When the reflected light is reddish, I suspect that it is the blood in the retina causing this colouration. Although you don’t see any scientific analysis of this topic.

The tapetum lucidum is made of cells with crystals which allows it to be reflective. And as the light entering the eye – which impinges upon the retina – passes through the retina and is reflected back to once again impinge upon the retina, it means the cat can see very well in the dark. The retina has a double opportunity to pick up the image as focused by the lens of the eye, which it converts to an electrical signal which is sent to the brain to interpret as an image.

Apparently, the reflective compound in the tapetum lucidum is riboflavin, a type of vitamin B. Riboflavin amplifies light to a specific wavelength which cats can see well and which also helps to increase the sensitivity of the retina to low light conditions.

Most other animals don’t have eyes like cats. Cats’ eyes are uniquely adapted to hunting and stalking. It is said that the reason why the pupil forms a slit rather than being circular is because it allows a cat to better judge depth and in doing so is better able to stalk prey successfully. Also, the slit pupil is better able to shutter the eye from bright light because it works in combination with the eyelid which passes down over it.

And the eyes of domestic cats are unusually large in relation to the size of their head. Remarkably, it is said that if people had eyes like cats, they would measure about 8 inches across. Cats’ eyes have a particularly large cornea which allows a greater amount of light enter to the back of the eye.

Also, both eyes are situated at the front of the head which allows them to use binocular vision to judge distances accurately. Sometimes this ability is enhanced by the cat swaying their head left and right before jumping onto a small object in order to precisely locate that object using binocular vision.

And the field of vision of the domestic cat is about 200° which allows them an extraordinary level of peripheral vision, with an overlap or binocular vision of about 140°.

Cats are not good at seeing objects close to them and are farsighted about 20/100 compared to normal human vision of 20/20. The reason is because the muscles that change the shape of the lens are quite weak and therefore the lens cannot refocus to close objects. Cats use their excellent sense of smell to check out their food which is under their noses but not their eyes!

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