Pharmacologic Pupil Testing and Imaging for Horner Syndrome
Anisocoria greater in the dark than in the light suggests an oculosympathetic lesion in the smaller pupil due to poor dilation. The presence of an ipsilateral mild ptosis (Mueller muscle) and/or upside down ptosis and a miotic pupil with impaired dilation (dilation lag) suggests a Horner syndrome. The three neuron, oculosympathetic pathway originates in the hypothalamus and descends in the brainstem and spinal cord (first order) then ascends over the apex of the lung in to the sympathetic chain (second order) to synapse in the superior cervical ganglion. The third order neuron travels with the internal carotid artery to the cavernous sinus where it accompanies cranial nerve VI (short course) and then V1 to enter the orbit. Pharmacologic testing (e.g., topical apraclonidine, cocaine) can establish a diagnosis of a Horner syndrome. Imaging studies of the entire oculosympathetic pathway can be diagnostic for potentially life threatening etiologies.
KeywordsAnisocoria Horner syndrome Dilation lag
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