Is it normal for optic nerve tumors to cause impairment in vision (neurofibromatosis 1)?

Usually. The symptoms are caused by tumor growing and pressing on the optic nerve and nearby structures. Symptoms may include: •involuntary eyeball movement, eyes bulging outward, squinting, loss of vision in one or both eyes leading to eventual blindness this may be losso of peripheral vision or more general loss.
Possible. Neurofibromatosis type i can sometimes involve optic nerve gliomas (tumors of the main nerve for the eye), and this can definitely affect vision. Discuss your symptoms with your doctor.