Fourth nerve palsy is a condition caused by weakness or paralysis of the superior oblique muscle. This condition often causes vertical double vision as the weakened muscle prevents the eyes from moving in the same direction together.
Because the fourth cranial nerve is the thinnest and has the longest course of the cranial nerves, it is particularly vulnerable to traumatic injury.
To compensate for the double-vision resulting from the weakness of the superior oblique, patients characteristically tilt their head down and to the side opposite the affected muscle.
When present at birth, it is known as congenital fourth nerve palsy.
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