Usher syndrome: The most common disease that diminishes both hearing and vision, a group of genetic disorders in which retinitis pigmentosa (an eye disease that causes vision to deteriorate over time) is combined with congenital deafness. The hearing loss in a patient with Usher syndrome occurs in both ears as a result of nerve deafness. Some patients also have balance problems because of lack of vestibular reflexes for balance. About half of all deaf-blind people have Usher syndrome. The syndrome is inherited in an autosomal recessive manner.