A 49-year-old female without systemic illness started complaining of hazy vision in the right eye four days ago. She complains of a mild double vision with an extreme lateral gaze. At the office, she is found to have 20/100 acuity on the right eye and bilateral horizontal nystagmus. Also, she has a prominent intention tremor on the right hand with a scanning speech. There is no motor weakness; soft and deep pain is normal. What is the most probable diagnosis causing her symptoms?
A. Multiple sclerosis
B. Parkinson's disease
C. Wilson's disease
D. Systemic lupus erythematosus