A 30-year-old man with relapsing remitting multiple sclerosis on interferon therapy has new onset right visual loss for one week. Clinically he has normal visual acuity on the left eye. However, he has only count "fingers on the right eye with right relative pupillary reflex. His fundus examination is normal. Rest of neurological exam is normal. His laboratory investigations within normal limits. What will be the most appropriate treatment for him?