Adrenergic iris neurons were pharmacologically studied in 30 migraineurs, 11 cluster headaches and 30 controls.
The pupillary diameter was measured by photographic technique. When compared with controls, migraineurs showed minor fenfluramine mydriasis and greater, more prolonged guanethidine miosis. No significant differences between the affected and unaffected side were observed by testing with guanethidine in unilateral migraineurs.
A poor concentration and synthesis of noradrenaline in the pupil terminals is hypothesized. Moreover, increased mydriasis observed with phenylephrine suggests alpha adrenoceptor supersensitivity from a defect of neuronal transmitter.
In cluster headaches, only a minor tyramine mydriasis was found in the affected pupil. This suggests low availability of neuronal transmitter or a defect of the synaptic tyramine re-uptake in the affected cluster pupil. A disorder of the iris adrenergic neurons could mirror an impairment in the central aminergic systems of idiopathic headaches.