Autonomic control of the eye and the iris

The vertebrate eye receives innervation from ciliary and pterygopalatine parasympathetic and cervical sympathetic ganglia as well as sensory trigeminal axons. The sympathetic and parasympathetic pathways represent the classical “core” of neural regulation of ocular homeostasis. Sensory trigeminal neurons are also involved in autonomic regulation by both providing the afferent limb of various reflexes and exerting their peptide-mediated local effector function. This arrangement is remarkably conserved throughout vertebrate classes although significant modifications are observed in anamniotes, in particular their irises. In higher primates and birds, intrinsic choroidal neurons emerged as a significant additional innervation component. They most likely mediate local vascular regulation and other local homeostatic tasks in foveate eyes. This review across the vertebrate classes outfolds the complex neuronal regulatory underpinnings across vertebrates that ensure proper visual function.