Autonomic components of the human pupillary light reflex.

TLDR

The study investigates the autonomic components of the human pupillary light reflex using infrared pupillometry and selective cholinergic or alpha‑adrenergic blockade, and proposes that redilation is driven mainly by parasympathetic relaxation modulated by cholinergic inhibition of the dilator muscle and central sympathetic inhibition of the Edinger‑Westphal nucleus. Infrared pupillometry was performed with partial local cholinergic (tropicamide) or alpha‑adrenergic (thymoxamine) blockade, and the pupillary response curve was analyzed using parameters identical or similar to those used in prior studies of autonomic components. Tropicamide increased baseline pupil area and altered five of eight response parameters, whereas thymoxamine lowered baseline area without affecting parameters, confirming a cholinergic contribution to the constrictive phase but revealing no peripheral alpha‑adrenergic activity during redilation.

Abstract

To investigate the autonomic components of the pupillary light reflex in humans, we used infrared pupillometry combined with a partial local cholinergic (tropicamide) or alpha-adrenergic (thymoxamine) blockade. The pupillary response curve was analyzed using parameters identical or similar to those employed previously to study the autonomic components of the pupillary light reflex. Tropicamide increased baseline pupil area and affected five of the eight measured parameters. Thymoxamine lowered baseline pupil area but did not affect any of the parameters. We found the expected cholinergic contribution to the constrictive phase of the pupillary light reflex but no evidence for peripheral alpha-adrenergic activity during redilation. We propose that redilation primarily involves parasympathetic relaxation, modulated by cholinergic inhibition of the dilator muscle and central sympathetic inhibition of the Edinger-Westphal nucleus.