Optic Neuritis

Which of the following is the most common site of demyelination in optic neuritis?

A 32-year-old woman with a 3-month history of optic neuritis in the right eye (now recovered to 6/9 vision) presents for follow-up. MRI brain at the time of optic neuritis showed one T2 hyperintense lesion in the right optic nerve and two additional demyelinating lesions in the periventricular white matter. She is asymptomatic neurologically. What is the most appropriate next step in management?

A 28-year-old woman presents with acute loss of vision in the left eye over 24 hours. She reports pain on eye movements and colour vision appears washed out. Examination reveals a relative afferent pupillary defect (RAPD), normal fundus appearance, and visual acuity of 6/60 in the affected eye. MRI brain with contrast shows T2 hyperintense lesions in the periventricular and juxtacortical regions. What is the most likely diagnosis?

A 28-year-old woman presents with sudden onset of painless vision loss in the right eye over 6 hours. She reports eye pain on lateral gaze and mild headache. On examination, visual acuity is 6/60 in the right eye with a relative afferent pupillary defect (RAPD). Fundoscopy shows a normal-appearing optic disc. MRI brain with contrast reveals T2/FLAIR hyperintense lesions in the periventricular and infratentorial regions. What is the most likely diagnosis?

A 32-year-old man presents with progressive blurring of vision in the left eye over 4 days, accompanied by pain on eye movements. He denies any systemic symptoms or prior neurological illness. Visual acuity is 6/36 in the left eye with a positive RAPD. Fundoscopy shows mild optic disc swelling with blurred margins. Formal visual field testing reveals a central scotoma. What is the most appropriate first-line investigation to confirm the diagnosis and assess for demyelinating disease?