We all admire the bright, colourful and shining eyes of a cat. But apart from the colourful prettiness, it also has some unique features.
Fellow blogger (Mr. Amit Misra, pradyot.net) gave a constructive suggestion that instead of always writing about amazing creatures, sometimes strange facts about our everyday creatures also could be written. In addition, today is 181st birthday of French ophthalmologist Ferdinand Monoyer (who invented the eye testing visual acuity chart). So this post is about the special characteristics of the eyes of our domestic cat.
It is assumed that cats can see in total darkness, but this is not true. However, cats can see clearly in only one sixth amount of light that we humans require to see. All eyes have a lens through which the light passes and the amount of the light passing through the lens is controlled by an aperture or pupil. This light then falls on the retina to form an image. The retina is rich with receptor cells — rods and cones. The rods detect light and the cones detect colour.
In the cats, this rods to cone ratio is higher than that in the humans. So, they can detect much more light and have a better vision in dim light. Higher count of rod cells also allows the cats to detect even slightest movement.
The shape of the cat’s pupil is like a slit or elliptical shaped. The opening and closing movements of such pupil are faster than the round pupil of human eye. This helps the cat to quickly adjust to the changes in the surrounding light. (Therefore the cats do not get blinded by sudden brightness like we do).
When the light is in abundance, the slit-like pupil closes to reduce the amount of light entering the eye and thus protects the sensitive retina.
The cats are considered as colourblind; however, they do see the colours but in much less intense hues. The receptors cone cells which are responsible for colour detection are less in number and these cells are not concentrated. So, for the cats some colours are muted than they are to us. They can differentiate blue-violets better than the red side of the colour spectrum.
The cats have a layer of reflective mirror-like cells at the back of the retina. These cells are called as Tapetum lucidum. These cells collect and reflect all the available light within the eyes and so the cats are able to see even when there is hardly any light. These same reflective cells give a jewel like shine to the cat’s eyes in the darkness of the night.
Most nocturnal carnivores and deep sea animals have this layer of cells. It improves the ability to see in the dark but reduces visual acuity.