NBEO Neuroscience Practice Test 2026 – Your All-in-One Guide to Exam Success!

Oculomotor nerve palsy affects both eye movement and parasympathetic control of the pupil and lens. When this nerve is weakened, you get ptosis from loss of the levator palpebrae superioris, and the eye tends to sit down and outward because the unopposed lateral rectus and superior oblique pull it that way, producing diplopia. If the parasympathetic fibers are involved, the pupil becomes fixed and dilated and accommodation is impaired due to ciliary muscle weakness. This combination—ptosis, a down-and-out eye, diplopia, and pupil involvement with a fixed dilated pupil and impaired accommodation—captures the classic presentation. If the pupil is spared, you can still have movement problems and ptosis, which fits microvascular causes, whereas pupil involvement often points to compressive lesions like an aneurysm. The other options describe incomplete or mismatched signs, such as no diplopia, preserved pupil responses, or normal motility with isolated dilation, which don’t fit the full CN III palsy picture.