Pharmacology of the human iris: development and use of challenge strategies in the study of antidepression response.

Basic physiological and neurochemical control mechanisms of human iris musculature are reviewed. The advantages and limitations of using pupillary responses to cholinergic and adrenergic drug challenges as peripheral indices of neuronal receptor sensitivity, are examined. A group of 15 depressed patients were tested with ocular instillation of pilocarpine and phenylephrine before and during treatment with Tranylcypromine. No change of pilocarpine sensitivity was found. A significant enhancement of phenylephrine sensitivity during weeks 3-5, but not during the first or second week of treatment was noted. The above potentiation of alpha-adrenergic responsiveness was correlated with clinical recovery.