Oculosympathetic

Oculosympathetic refers to the sympathetic innervation that affects the eye and its adnexa, including the pupil, eyelid, and facial sweat glands. It is mediated by the oculosympathetic pathway, a three-neuron chain that courses from the brain to the eye.

Anatomy and pathway: The first-order neuron begins in the hypothalamus and descends to the ciliospinal centre of Budge at the level of the spinal cord (C8 to T2). The second-order, or preganglionic, fibers exit the spinal cord and ascend the sympathetic chain to the superior cervical ganglion. The third-order, or postganglionic, fibers travel from the superior cervical ganglion with the internal carotid plexus to the dilator pupillae muscle in the iris, the Mueller (superior tarsal) muscle of the eyelid, and, to some extent, to sweat glands of the face.

Functions: The oculosympathetic fibers control sympathetic dilation of the pupil, subtle elevation of the upper eyelid, and autonomic innervation of certain facial sweat glands. Disruption of this pathway can affect pupil size, eyelid position, and facial sweating.

Clinical relevance: Impairment of the oculosympathetic pathway can cause Horner syndrome, characterized by ptosis, miosis, anisocoria that is more evident in the dark, and sometimes facial anhidrosis or enophthalmos. Causes range from central lesions (e.g., brainstem or hypothalamic disease) to preganglionic etiologies (e.g., thoracic outlet or apical lung tumors) and postganglionic issues (e.g., carotid dissection).

Diagnosis and evaluation: Clinicians may use pharmacologic tests such as apraclonidine or cocaine tests to confirm sympathetic denervation, followed by imaging (MRI/CT) to identify an underlying lesion, especially when Horner syndrome is present.