New Observations Regarding the Anatomy of the Pupillary Light Reflex: Animal Studies

In humans and other primates, an increase in luminance in either eye elicits bilateral pupilloconstriction that is essentially equal in both eyes. Our current thinking regarding the subcortical pathway for this pupillary light reflex owes much to the early studies of Magoun and Ranson and to later studies of Carpenter and colleagues. Textbook models of the pupillary light reflex pathway explain the behavior of this clinically-important reflex by proposing that a pretectal nucleus receives direct retinal input and projects bilaterally to the Edinger-Westphal nucleus, which contains the parasympathetic, preganglionic neurons controlling pupilloconstriction.