The optic nerve is a part of the white matter in the central nervous system and can easily be observed with a funduscope. Neuro-ophthalmologic studies of the optic nerve is useful in monitoring disorders in the central nervous system. In this paper we presented four cases of optic nerve diseases and discussed them from the standpoint of neuro-ophthalmology. Case 1, a 9-year-old girl, had left retrobulbar optic neuritis and right papillitis which occurred one year after the onset of left optic neuritis. She was treated with a three day course of methylprednisolone (500 mg). Her left optic disc became atrophic, but her right optic disc became normal. Her visual acuity recovered to 1.0 in each eye. Relative afferent pupillary defect was seen in her left eye. Steroid therapy for optic neuritis and pupillary light reaction were discussed. Case 2 was a 7-year-old girl with teratoma in the chiasmal region, and case 3 was a 10-year-old boy with craniopharyngioma. Visual field changes caused by tumors in the chiasmal region were discussed. Case 4 was a 7-year-old boy with right optic atrophy and left papilledema, an example of Foster Kennedy syndrome. The effects of papilledema on visual function was discussed.