Sympathetic pupillary activity in infants.

In an attempt to learn the contribution of the sympathetic system to smaller pupillary size in infants, pupillary responses were tested to agents acting on this system in 12 ihfants and 23 young adults. Phenylephrine dilated the pupils of both groups by the same ratio, with infants' pupils reaching a lesser diameter. The responses to cocaine and hydroxyamphetamine were lower in children. It is concluded that in the first months of life the postganglionic sympathetic nerve releases less norepinephrine. This may be due to a lower number of sympathetic neurons. The post-synaptic apparatus may not be fully developed in infants.