What is the commonest cause of loss of vision in Neurofibromatosis type 1?

Optic nerve glioma ,pilocytic astrocytoma, typically occurs in young children. It gives a fusiform enlargement of nerve and may present with -slowly |sing painless proptosis, -visual impairment (often marked), -optic atrophy -strabismus. Can be B/L and may extend posteriorly to involve chiasma, optic tract and hypothalamus. Hamaomatous lesions (Lisch nodules) are found on iris of pre pubeal children who suffer from Neurofibromatosis. Generally do not cause loss of vision. Acoustic neuroma (CP angle tumour ) is seen in NF type 2. NF Type 1 can also be associated with glaucoma