ROLE OF SYMPATHETIC AND PARASYMPATHETIC SYSTEMS IN REFLEX DILATATION OF THE PUPIL

Abstract

THE ROLE of the sympathetic and parasympathetic mechanisms in the dilation reflexes of the pupil is still under discussion. Originally the cervical portion of the sympathetic chain was thought to be responsible for pupillary dilation; this belief was held until, back in 1861, Balogh¹discovered that reflex dilation persisted after excision of the superior cervical ganglion. In 1878 C. R. Vulpian²observed reflex dilation after removal of both the upper cervical and the stellate ganglion; he concluded that this dilation was mediated by sympathetic dilator fibers outside the cervical sympathetic chain. In 1883 von Bechterew³suggested that pupillary dilation to pain stimuli might be caused by inhibition of the third nerve, rather than by impulses running over the peripheral sympathetic fibers. Braunstein⁴expressed himself in favor of Bechterew's hypothesis, since, after having cut the third nerve intracranially, he could no longer obtain reflex dilation to pathic