A 26 year-old female presents to the emergency department with reduced vision in the left eye. There is no associated pain. She has had an episode of painless visual loss in the right eye 6 months ago. She has previously been investigated for episodes of numbness of the right arm and the left leg which lasted a few weeks each before making a near complete recovery. Fundoscopy reveals bilateral optic disc pallor. Her visual acuity is 10/20 on the right, but reduced to finger counting on the left. A MRI performed 6 months ago is shown below. She is given a course of oral methylprednisolone, but her visual acuity in the left eye does not improve after two weeks. Which of the following is most likely to be found?