A 24-year-old bme student was studying late at night for an examination. as he looked at his textbook, he realized that his left arm and left leg were numb. he dismissed the complaint, recalling that 6 or 7 months ago he had similar symptoms. he rose from his desk and noticed that he had poor balance. he queried whether his vision was blurred, and remembered that he had some blurred vision approximately 1 to 2 years earlier, but that this resolved. he had not seen a physician for any of these previous symptoms. he went to bed and decided that he would seek medical consultation the next day. the blurry vision 2 years ago was most likely: