MRCP2-2971
A 65-year-old woman presents with a three-month history of diplopia and blurred vision in her left eye. She reports no pain or other neurological symptoms and has no significant medical history except for smoking 20 cigarettes per day and drinking alcohol in moderation.
During her examination, her right eye has a visual acuity of 6/6 while her left eye is only 6/36. She has left partial ptosis and mild proptosis with conjunctival injection. The left pupil is smaller than the right but reacts normally to light. There is some limitation of abduction of the left eye, and fundoscopy reveals a pale left optic disc. The left corneal reflex is reduced, but the remainder of her neurological examination is normal.
Routine blood tests, including a full blood count, urea and electrolytes, liver function tests, thyroid function, serum calcium, serum creatine kinase, and autoantibody screen, were all normal. Her electrocardiogram and chest radiograph showed no abnormalities. Slit lamp examination was normal, and intraocular pressures were within the normal range.
Based on these findings, where is the most likely site of the lesion causing her symptoms?