Congenital Horner syndrome is a rare neurological disorder characterized by relative pupillary miosis and blepharoptosis, evident at birth, caused by interruption of the oculosympathetic innervation at any point along the neural pathway from the hypothalamus to the orbit. Often additional symptoms, such as enophthalmos, facial anhidrosis, iris heterochromia, conjunctival congestion, transient hypotonia and/or pupillary dilation lag, may be present. Association with birth trauma, neoplasms or vascular malformations has been reported. The disease is Monarch Disease Ontology term MONDO_0007735 (congenital Horner syndrome). Also known as: congenital Claude-Bernard-Horner syndrome, congenital Horner syndrome (disease).