4th June 2023

A 70-year-old gentleman presents with a severe headache and double vision

A 70-year-old gentleman presents with a severe headache and double vision. He has a past medical history of type 2 diabetes mellitus, hypertension, and osteoarthritis. On examination, he has complete ptosis of the right eye, which is held downwards and outwards. His right pupil is fixed and non-reactive to light. What is the most likely underlying cause?