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The pupillary light reflex (PLR) or photopupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity of light that falls on the retinal ganglion cells of the retina in the back of the eye, thereby assisting in adaptation of vision to various levels of lightness/darkness.
The pupil function or aperture function describes how a light wave is affected upon transmission through an optical imaging system such as a camera, microscope, or the human eye. More specifically, it is a complex function of the position in the pupil [ 1 ] or aperture (often an iris ) that indicates the relative change in amplitude and phase ...
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 (accommodation) and is controlled by the ciliary muscle.
The Stiles–Crawford Effect is quantified as a function of distance (d) away from the center of the pupil using the following equation: () =,where η is the relative luminance efficiency, and d is defined as positive on the temporal side of the pupil and negative on the nasal side of the pupil.
Some skates and rays have crescent shaped pupils, [17] gecko pupils range from circular, to a slit, to a series of pinholes, [18] and the cuttlefish pupil is a smoothly curving W shape. Although human pupils are normally circular, abnormalities like colobomas can result in unusual pupil shapes, such as teardrop, keyhole or oval pupil shapes ...
Muscles around the iris change the size of the pupil, regulating the amount of light that enters the eye [3] and reducing aberrations when there is enough light. [4] The eyes of most cephalopods, fish, amphibians and snakes have fixed lens shapes, and focusing is achieved by telescoping the lens in a similar manner to that of a camera. [5]
The state of the pupil is closely influenced by various factors, primarily light (or absence of light), but also by emotional state, interest in the subject of attention, arousal, sexual stimulation, [24] physical activity, [25] accommodation state, [26] and cognitive load. [27] The field of view is not affected by the size of the pupil.
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.