Pupillary light reflex

Lesions of the afferent pathway.

• • Lesions of the optic radiation, visual cortex, or sup. colliculi have no effect on the pupillary light reflex.

  • A lesion of the pretectal area, h/e, abolishes the reflex.

  • This indicates that the former structures don't participate in the reflex arc, and that the afferent arm of the reflex arc must traverse the pretectal area, though the precise anatomical localization of this pathway isn't yet fully clear.

  • Similarly, optic nerve lesions, which interrupt the afferent arm of the reflex arc at a different site, impair the pupillary response to illumination of the eye on the side of the lesion: neither the ipsilat. nor the contralat. pupil will constrict nmlly.

  • Illumination of the other eye is followed by nml constriction of both pupils.

  • These fi imply the presence of an afferent papillary defect.

Lesions of the efferent pathway.

• • If the oculomotor nerve or ciliary ganglion is damaged, the impulses from the Edinger-Westphal nucleus can no longer reach the sphincter pupillae musc. of the ipsilat. eye.

  • The result is mydriasis w/ absence of the light reflex.