Which CN palsy is the closest differential to Divergence Insufficiency?

Which CN palsy is the closest differential to Divergence Insufficiency?

• A. CN 3 Palsy
• B. CN 6 Palsy
• C. CN 4 Palsy
• D. CN 5 Palsy

Answer: (B)

Divergence relies on the lateral rectus to move the eyes outward for distance viewing. When divergence is insufficient, you get an exodeviation that is worse at distance, with relatively preserved near alignment. The closest differential to this pattern is a sixth nerve palsy, because weakness of the lateral rectus directly reduces outward movement, producing exotropia that resembles divergence insufficiency—especially more pronounced when viewing at distance. In a CN VI palsy you’ll typically see limited abduction of the affected eye, matching the outward drift seen in divergence-related cases. Other cranial nerve palsies don’t fit this horizontal divergence pattern as well: a CN III palsy disrupts several muscles and often alters eyelid position and vertical or complex misalignment; a CN IV palsy causes vertical misalignment and torsion; a CN V palsy affects sensation and mastication and does not primarily produce the divergence-type exotropia described here.

Divergence relies on the lateral rectus to move the eyes outward for distance viewing. When divergence is insufficient, you get an exodeviation that is worse at distance, with relatively preserved near alignment. The closest differential to this pattern is a sixth nerve palsy, because weakness of the lateral rectus directly reduces outward movement, producing exotropia that resembles divergence insufficiency—especially more pronounced when viewing at distance. In a CN VI palsy you’ll typically see limited abduction of the affected eye, matching the outward drift seen in divergence-related cases.

Other cranial nerve palsies don’t fit this horizontal divergence pattern as well: a CN III palsy disrupts several muscles and often alters eyelid position and vertical or complex misalignment; a CN IV palsy causes vertical misalignment and torsion; a CN V palsy affects sensation and mastication and does not primarily produce the divergence-type exotropia described here.