The pupillary light reflex pathway

Abstract

Since Wernicke¹ publicized the matter in the 1880s, it has been considered practically a ‘law of nature’ that the pupillary light reflex pathway is a simple brainstem reflex. The afferent arc is formed by the retinal receptors, bipolar and ganglion cells; the impulse travels to the pretectal nuclei in the dorsal midbrain, and via the intercalated neurons to the Edinger-Westphal subnu-cleus of the ocular motor nucleus, and finally reaches the iris along the efferent arc carried by the oculomotor nerve and the short ciliary nerves. Thus, the pupillary light reflex was thought of as a purely subcortical activity, which was entirely consistent with the involuntary character of pupillary function.