The trochlear nerve, also known as cranial nerve 4 (CN IV), controls the superior oblique muscle in your eye. This muscle allows you to move your eyeball down and shift your gaze from side to side.

Gong, Q., Janowski, M., Tang, H. et al. Magnetic resonance imaging of the functional anatomy of the superior oblique muscle in patients with primary superior oblique overaction. Eye 31 , 588–592 ...

In 1906 Duane reported the first case with uniocular rotatory nystagmus involving the superior oblique muscle. 1 In 1970 Hoyt and Keane termed SOM as an acquired abnormality in the innervation of ...