A syndrome associated with defective sympathetic innervation to one side of the face, including the eye. Clinical features include miosis; mild blepharoptosis; and hemifacial ANHIDROSIS (decreased sweating)(see hypohidrosis). Lesions of the brain stem; cervical spinal cord; first thoracic nerve root; apex of the lung; CAROTID ARTERY; cavernous sinus; and apex of the orbit may cause this condition. (From Miller et al., Clinical Neuro-ophthalmology, 4th ed, pp500-11)