Domestic cats have vertical pupils for two reasons:
- On a scientific level it is said that a vertical pupil provides better depth perception which allows a domestic cat to measure distance better and/or focus on prey better. A scientific study by researchers at the University of California, Berkeley, decided that with vertical slits, predators see vertical lines behind the point of focus quite sharply but horizontal lines at the same distance are blurred. This allows them to have a greater ability to pinpoint prey animals.
- The vertical pupil in conjunction with the eyelid allows the cat to restrict light to the retina more effectively than a circular pupil under bright light conditions. The eyelid passes down the vertical pupil like a blind which, to use a photographic term, stops down the lens to a smaller aperture than normal. This is needed to protect the retina which has a mirror-like film behind it (the Tapetum lucidum), which reflects light back to magnify the capture of light so that they can see better under dark conditions.
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