June 13, 2014
Experts' Expert: How cats see in the dark
C. Claiborne Ray's June 2 New York Times Science section Q&A, below, explains how cats' eyes enable them to see far more than humans when darkness falls.
Q. Does the slit shape of a cat’s pupil confer any advantages over the more rounded pupils of other animals
A. "There are significant advantages," said Dr. Richard E. Goldstein, chief medical officer of the Animal Medical Center in New York City.
"A cat can quickly adjust to different lighting conditions, control the amount of light that reaches the eye and see in almost complete darkness," he said. "Moreover, the slit shape protects the sensitive retina in daylight."
The slit-shaped pupil found in many nocturnal animals, including the domestic cat, presumably allows more effective control of how much light reaches the retina, in terms of both speed and completeness.
"A cat has the capacity to alter the intensity of light falling on its retina 135-fold, compared to tenfold in a human, with a circular pupil," Dr. Goldstein said. "A cat’s eye has a large cornea, which allows more light into the eye, and a slit pupil can dilate more than a round pupil, allowing more light to enter in dark conditions."
Cats have other visual advantages as well, Dr. Goldstein said. A third eyelid, between the regular eyelids and the cornea, protects the globe and also has a gland at the bottom that produces extra tears. The eyes' location, facing forward in the front of the skull, gives cats a large area of binocular vision, providing depth perception and helping them to catch prey.
Times illustration (top) by Victoria Roberts.
June 13, 2014 at 12:01 PM | Permalink