Horner syndrome is a clinical syndrome caused by damage to the sympathetic nervous system leading to ptosis (drooping upper eyelid from loss of sympathetic innervation to the Müller or superior tarsal muscle), upside-down ptosis (slight elevation of the lower lid), and miosis (constricted pupil) and dilation lag, anhydrosis (decreased sweating) on the affected side of the face, loss of ciliospinal reflex and blood shot conjunctiva may occur depending on the site of lesion
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