GUANETHIDINE AND PUPILLARY REACTION

Local application of guanethidine to the eye results in miosis. The sympathicolytic action of guanethidine on the pupil was proved by the consistent appearance of a Horner's syndrome after instillation of a 10% solution into the conjunctival sac. Lack of cocaine mydriasis and unimpaired adrenaline mydriasis after guanethidine application are further evidence of this mode of action. Guanethidine is the first drug that can be consistently relied upon to produce miosis by inhibiting sympathetic impulses to the intraocular pupillary muscles; it also inhibits sympathetic impulses to Horner's muscle of the upper lid. It is a reliable sympathicolytic agent for testing the reaction of abnormal pupils.