A 35-year-old man is brought to the emergency department with a 3-week history of progressive headache, vomiting, and blurred vision. On examination, blood pressure is 150/95 mmHg, and fundoscopy reveals bilateral optic disc swelling with blurred margins, obscuration of vessels at the disc, and cotton-wool spots. Visual acuity is 6/6 bilaterally. There is no pain on eye movement. What is the most likely diagnosis?