The amount of light entering the eye is restricted by the aperture in the iris, the pupil. In a dark room, a person’s pupils are large, perhaps 8 mm (0.3 inch) or more in diameter. When the room is lighted, there is an immediate constriction of the pupils, the light reflex. This is bilateral, so that even if only one eye is exposed to the light, both pupils contract to nearly the same extent. After a time, the pupils expand even though the bright light is maintained, but the expansion is not large. The final state is determined by the ...(100 of 31643 words)