Fourth cranial nerve
palsy or trochlear nerve palsy, is a condition affecting cranial nerve 4 (IV),
the
trochlear nerve
The trochlear nerve (), ( lit. ''pulley-like'' nerve) also known as the fourth cranial nerve, cranial nerve IV, or CN IV, is a cranial nerve that innervates a single muscle - the superior oblique muscle of the eye (which operates through the pu ...
, which is one of the
cranial nerves
Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and f ...
. It causes weakness or paralysis of the
superior oblique muscle
The superior oblique muscle or obliquus oculi superior is a fusiform muscle originating in the upper, medial side of the orbit (anatomy), orbit (i.e. from beside the nose) which abducts, depresses and internally rotates the eye. It is the only e ...
that it innervates. This condition often causes vertical or near vertical double vision as the weakened muscle prevents the eyes from moving in the same direction together.
Because the trochlear nerve is the thinnest and has the longest intracranial 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.
See also
*
Harada–Ito procedure
References
External links
Disorders of ocular muscles, binocular movement, accommodation and refraction
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