Are you legaly blind when you have optic nerve atrophy?

Optic atrophy. Legal blindness is usually defined by having visual acuity worse than 20/200 or loss of a certain amount of visual field (peripheral vision). The legal definition can vary from one state to another. See your eye doctor for more information.
Not necessarily. Optic atrophy can occur from several etiologies that do not reduce the central vision to 20/200 or worse or severely constrict the visual field. Those are the criteria that need to be met to consider a person legally blind.