Have you ever wondered why cat’s eyes are the way they are? In bright light the pupils of cats look like slits whereas in dim light their pupils look circular. I have documented this phenomenon in the pictures of Science Cat below.
Cats are predators that are biologically designed to hunt at night. The shape of cat’s pupils is an adaptation that reduces the amount of glare during the day and increases the amount of light that enters the eyes during the night. Whereas circular pupils such as those of humans can expand their area 15-fold in going from a fully constricted to a fully dilated shape, those of cats undergo a 135-fold change during this transition. But what allows cats to see better at night is that the density of a type of light receptor in their eyes called “rods” is 6 to 8 times higher than that of a human. Rods permit the detection of very faint light signals. Additionally, cats have a layer of tissue in the back of their retinas called the tapetum lucidum which reflects light back into the light receptors of the eye increasing the amount of light that they can detect. This is why if you use flash photography at night on a cat, like I did with Science Cat below, they look like little demons!
The photographs of Science Cat are property of the author and can only be used with permission.
The reflection of light by the eyes is considered by many painters to be an important detail that can make or break the whole painting in terms of making it look lifelike, and such reflection has been depicted by various painters over the years in many shapes and locations on the pupil and iris of the eyes of the individuals they painted. Below is a sampler that I have put together from my collection of photographs.
Painting of Russian Princess Anna Alexandrovna Galitzin by Elisabeth Louise Vigee Le Brun (c. 1797). Baltimore Arts Museum, Baltimore, U.S.A.
Painting of Eunice Brown Fitch, wife of American businessman Timothy Fitch, by Joseph Blackburn (1760). Peabody Essex Museum in Salem, Massachusetts, U.S.A.
Painting of Archduchess Maria Karoline of Austria when she was Princess-Abbess of the Theresian Royal and Imperial Ladies Chapter of the Castle of Prague from 1844 to 1852 (painter unknown). Rosenberg Palace, Prague Castle, Prague, Czech Republic.
Painting of American art collector and Amateur photographer Sarah Lawrence Brooks by John Singer Sargent (1890). The Peabody Essex Museum in Salem, Massachusetts. U.S.A.
But the importance of depicting the reflection of light by the eyes goes beyond art. For some living things it can be a matter of life and death. Many butterflies, moths, and caterpillars have evolved eye spots on their wings or bodies that imitate eyes to deter predators, and these eye patterns also have spots that mimic that twinkle in the eyes!
Butterfly image from pikist is free for use under a public domain license. All other photographs are property of the author and can only be used with permission.