Question

a patient has horizontal diplopia that worsens when looking at distant objects. what is the most likely diagnosis?
trochlear nerve palsy
abducens nerve palsy
bells palsy
optic neuritis

Explanation:

• Trochlear nerve palsy: Usually causes vertical diplopia, not horizontal.
• Abducens nerve palsy: The abducens nerve (cranial nerve VI) innervates the lateral rectus muscle. When there is abducens nerve palsy, the eye cannot abduct (move outward). Horizontal diplopia that worsens at distance (because when looking at distant objects, the eyes need to be more abducted for binocular vision) is a key feature.
• Bell's palsy: Affects the facial nerve (cranial nerve VII) and causes facial muscle weakness (e.g., drooping of one side of the face), not diplopia.
• Optic neuritis: Affects the optic nerve (cranial nerve II) and causes visual loss (e.g., decreased visual acuity, central scotoma), not diplopia.

Answer:

Abducens nerve palsy