Tuesday, 28 June 2011
Night Vision in Cats
Cats have elliptical pupils that are oriented vertically. This elliptical pupil allows it to open much larger than a human’s round pupil. The larger pupil lets in more light and enhances a cat’s vision in low light.
Another important feature of a cat’s eyes is a membrane called the tapetum lucidum. The tapetum is designed to reflect light within the eye itself and allow more light to reach the retina. The flash of a cat’s eyes in the dark, or “eyeshine” that we see, is light reflecting off of the cat’s tapetum.
The cat’s retina is also designed for vision in low light conditions because it is made up of many more rods than cones. Rods are more effective than cones at absorbing light. Cones are responsible for absorbing color and yielding color vision, which is more limited in cats than humans. Much like dogs, cats see blues and violets better than reds.
The large pupil and reflective tapetum maximize the light that reaches the retina, which is saturated with rods that are very effective at absorbing light. The structures all work together to send a signal along the retinal nerve to produce an image in the cat’s brain, even in the dark of night. The image to the right demonstrates the enhanced image a cat will see with its superior night vision.
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