Pupillary reflex

In medicine, the pupillary reflex or pupillary light reflex, is the reduction of pupilsize in response to light. It is a normal response and dependent on the function of the optic nervesand oculomotor nerves.

Pupillary constriction is sometimes used as a synonym for pupillary reflex but something more general. Pupillary constriction may be induced pharmacologically by parasympathomimeticsand is also seen in accommodation(when the eyes focus on something close).

Emergency roomphysiciansoften assess the pupillary reflex because it is useful for gauging brain stemfunction. Normally, pupils react (constrict) equally (or consenually). Lack of the pupillary reflex or an abnormal pupillary reflex can be caused by optic nerve damage, oculomotor nerve damage, brain deathand things that mimic brain death, such as barbiturates. The optic nerve is responsible for the afferentlimb of the pupillary reflex, or in other words, senses the incoming light. The oculomotor nerve is responsible for the efferentlimb of the pupillary reflex; in other words, it drives the muscles that constrict the pupil. Dependent on how the pupils constrict or do not constrict one can determine which of the cranial nervesis damaged.

If the optic nerveis damaged on one side: the pupil on that side will constrict if light is shone into the other eye. However, it will not constrict if light is shone in that eye. If the oculomotor nerveis damaged on one side the pupil will not constrict on that side. However, if light is shone into that eye (and the afferent limb of the reflex is intact) the other eye will constrict.

The reflex pathway consists of retinal ganglion cells, which convey information from the photoreceptorsto the optic nervewhich connects to the pretectal nucleusof the high midbrain. It bypasses the lateral geniculate nucleusand the primary visual cortex. From the pretectal nucleus neurons send axons to neurons of the Edinger-Westphal nucleuswhose axons run along both the left and right oculomotor nerves. Oculomotor nerve axons synapse on ciliary ganglionneurons whose axons innervate the constrictor muscle of the iris.

External links

Animation of pupillary light reflexpl:Odruch źreniczny

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It uses material from the http://en.wikipedia.org/wiki/Pupillary+reflex Wikipedia article Pupillary reflex.