TABLE EFFECT OF DRUGS ON THE PUPIL IN LESIONS OF DIFFERENT SYMPATHETIC NEURONES

HORNER'S syndrome classically consists of a tetrad of miosis, ptosis, enophthalmos, and anhidrosis on the affected side, though the last-mentioned is not a constant finding. It was first noted experimentally in 1852 by Claude Bernard, but it was not until 1869 that the findings were described by Johann Friedrich Horner, a Swiss ophthalmologist, who gave the syndrome its name (Bernard, 1853; Horner, 1869). Any interruption in the sympathetic pathway in its long course from the brain to the eye may be responsible for the syndrome on the affected side. The sympathetic pathway to the pupil consists of three neurones: (1) The central neurone commencing in the hypothalmic centre of the midbrain runs down to the ciliospinal centre in the cord. (2) The second or preganglionic neurone then passes via the ventral roots of C8-T3 to the sympathetic chain, and entering the inferior cervical ganglion it passes upwards to the superior cervical ganglion at the level of C2-3. (3) The third or post-ganglionic neurone passes via the carotid plexus and trigeminal nerve to the eye innervating the dilator pupillae and the involuntary muscles of the eyelid. According to the scheme devised by Foerster and Gagel (1932), pharmacological tests are used to determine which neurone of the pathway is involved by any par-ticular lesion. These tests determine the actions of cocaine and adrenaline on the pupil. The possible results are shown in the Table