When a solution of epinephrin is instilled into the conjunctival sac, no noteworthy effect is produced on the pupil of the eye. After complete excision of a superior cervical ganglion of the sympathetic nervous system, however, similar introduction of epinephrin causes a dilatation of the pupil on the operated side. This was demonstrated by Meltzer1 at the Rockefeller Institute for Medical Research in 1904. The degree of pupillary dilatation depends on the quantity instilled. It can easily be made maximal and may last for some time. The myotic effect of physostigmin is also overcome by instillation of epinephrin.
The dilatation of the pupil is accomplished by the contraction of a muscle, the dilator pupillae, just as the constriction of the pupil is accomplished by the contraction of the constrictor pupillae. These muscles are exact antagonists. When one is contracted the other is relaxed; and it seems to be an
THE SIGNIFICANCE OF THE PUPILLARY REACTION TO EPINEPHRIN. JAMA. 1915;LXIV(23):1916-1917. doi:10.1001/jama.1915.02570490032018