It is an asymmetry of the size of the pupils, due to a dilation of this structure, either due to a myosis or an abnormal and unilateral mydriasis. Causes: a) vascular: cerebral vascular accidents, brain aneurysms. b) tumor: brain, Claude Bernard-Horner syndrome produced by thoracic tumors c) infectious: meningitis, encephalitis, brain abscess d) ophthalmological drugs: atropine, cyclopentolate and phenylephrine. E) others: glaucoma. The abrupt origin, after a brain injury, points to a possible hemorrhagic cause; On the other hand, a picture of gradual appearance, with a history of headache, double vision, explosive vomiting, points more to a tumor pathology. If there is fever and headache, in addition to a stiff neck, meningitis may be considered. If the onset is sudden, with severe eye pain or headache, and loss of vision in one eye, then glaucoma should be considered.

Treatment: It depends on the underlying cause, but the most common cause is the focal lesion.