What is trochlear nerve palsy (fourth nerve palsy)?

Updated: Oct 08, 2019
  • Author: Zafar A Sheik, MD, MD; Chief Editor: Andrew G Lee, MD  more...
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Trochlear nerve palsy is mentioned in ophthalmology texts dating to the mid nineteenth century. However, it received little more than a brief mention and was no doubt an underrecognized entity. In 1935, Bielschowsky correctly noted that trochlear nerve palsy was the most common cause of vertical diplopia and introduced his classic head-tilt test. With greater clinical interest, the number of identified fourth nerve palsies has increased.

Key Considerations

A fourth nerve palsy is a common cause of binocular vertical oblique diplopia in isolation.

The fourth cranial nerve exits dorsally and has the longest intracranial course.

An isolated fourth cranial nerve palsy can usually be diagnosed using the three-step test.

The primary action of the superior oblique muscle is intorsion.

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