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In humans, the pupil is circular, but its shape varies between species; some cats, reptiles, and foxes have vertical slit pupils, goats and sheep have horizontally oriented pupils, and some catfish have annular types. [3] In optical terms, the anatomical pupil is the eye's aperture and the iris is the aperture stop.
The human eye, showing the iris and pupil. In 1802, philosopher William Paley called it a miracle of "design."In 1859, Charles Darwin himself wrote in his Origin of Species, that the evolution of the eye by natural selection seemed at first glance "absurd in the highest possible degree". [3]
The pupil of the human eye can range in size from 2 mm to over 8 mm to adapt to the environment. The human eye can detect a luminance from 10 −6 cd/m 2, or one millionth (0.000001) of a candela per square meter to 10 8 cd/m 2 or one hundred million (100,000,000) candelas per square meter.
In humans, eye color is a highly sexually dimorphic trait. [18] Several studies have shown that men are more likely to have blue eyes than women, while women are more likely to have darker eye colors (green and brown eyes) than men. [18] [19] Sex is therefore a major factor in the expression of eye color genotypes. [18]
Pupils of both sexes dilated after seeing pictures of people of the opposite sex. In females, the difference in pupil size occurred also after seeing pictures of babies and mothers with babies. This examination showed that pupils react not only to the changes of intensity of light (pupillary light reflex) but also reflect arousal or emotions.
Chief rays and marginal rays determine the location and the size of the entrance pupil, respectively. A camera lens adjusted for large and small aperture. The visible opening is the entrance pupil of the lens. The apparent location of the anatomical pupil of a human eye (black circle) is the eye's entrance pupil location. The outside world ...
Ever wonder why seeing pictures of adorable puppies turns humans into piles of emotional mush? Stanford University Professor Robert M. Sapolsky looked into the phenomenon and came up with some ...
Researchers examined the effect of head and eye movement on changing gaze direction in humans and other great apes. A human experimenter, observed by either a human infant, a gorilla, a bonobo, or a chimpanzee, did one of four actions: Tilted his head up while closing his eyes; Looked at the ceiling with his eyes while keeping his head stationary