What thin, circular structure in the eye controls the diameter and size of the pupils and the amount of light reaching the pupil?
Human eye μm) in thickness near its center. The posterior chamber constitutes the remaining five-sixths; its diameter is typically about 24 mm. The cornea and sclera are connected by an area termed the limbus. The iris is the pigmented circular structure concentrically surrounding the center of the eye, the pupil, which appears to be black. The size of the pupil, which controls the amount of light entering the eye, is adjusted by the iris' dilator and sphincter muscles. Light energy enters the eye through the cornea, through the pupil and then through the lens. The lens shape is changed for near focus
Pupil of all wavelengths across the full diameter of the lens, even in bright light. It has also been suggested that in ambush predators such as some snakes, vertical slit pupils may aid in camouflage, breaking up the circular outline of the eye. In a study of Australian snakes, pupil shapes correlated both with diel activity times and with foraging behaviour. Most snake species with vertical pupils were nocturnal and also ambush foragers, and most snakes with circular pupils were diurnal and active foragers. Overall, foraging behaviour predicted pupil shape accurately in more cases than did diel time of activity, because