With regard to the inclusion criteria: abnormalities of the optic nerve, retina disorders, glaucoma, Stargardt disease, macular degeneration, retinitis pigmentosa, congenital toxoplasmosis, congenital cataracts, congenital Leber's amaurosis, detached retina and astrocytoma. The exclusion criteria: medical diagnosis of injury affecting balance in the previous three years; use of medication affecting the central nervous system, coordination or balance; current symptoms of vertigo or dizziness; medical neurological diagnosis or symptoms suggestive of vestibular disorder; and past surgery or clinical condition of lower limbs or spinal column that can affect balance and gait. The subjects will be defined as independent if capable of locomotion without the assistance of others in all environments with or without the use of a guide stick.