This loss of vision in the peripheral visual field can be due to optic nerve damage caused by glaucoma, high internal eye pressure, retinal detachment, occlusion of blood supply as in eye stroke, optic neuritis,
and optic nerve edema. Tunnel vision is also possible after a history of head injury,
concussion, brain damage and stroke, though all these causes may not be applicable in your son's case. Do discuss this with your son's doctor. Take care!