MS-4080

A 32-year-old woman with a BMI of 32 kg/m² visits her general practitioner complaining of sudden onset diplopia. She reports that she experiences double vision mainly when reading. Apart from a chronic headache that worsens with Valsalva manoeuvres, she has no significant medical history.

During the examination, there is no anisocoria observed. However, her left eye has a slight medial deviation, and there is a defect in abduction on the same side.

Which cranial nerve is most likely affected in this patient?