Cardinal Positions of Gaze (Extraoccular movements)
To evaluate oculomotor function, ask the patient to keep his/her head still and visually track a bright light (pen light) along an “H” path. Evaluate the patient’s eye movements in each of the six cardinal positions of gaze. CN 3 (the oculomotor nerve) produces 4 of the 6 positions, CN 6 (the abducens nerve) produces 1 position, and CN 4 (the trochlear nerve) produces 1 position.
1. Eye muscle innervation.
A. The CN 3 innervates the majority of the extraocular muscles: the medial rectus, superior rectus, inferior rectus, and inferior oblique.
B. The CN 6 innervates the lateral rectus muscle.
C. The CN 4 innervates the superior oblique muscle.
2. Eye movements. The “H” path provides the six cardinal positions of gaze, which we divide into horizontal and vertical gaze.
A. Horizontal gaze comprises abduction (lateral rotation) and adduction (medial rotation).
a. The lateral rectus produces eye abduction.
b. The medial rectus produces eye adduction.
B. Vertical gaze comprises superior rotation (elevation) of the eye and inferior rotation (depression) of the eye. Different muscles are responsible for superior and inferior rotation depending on whether the eye is abducted or adducted.
a. When the eye is abducted, superior rectus directs the eye superiorly and inferior rectus directs the eye inferiorly.
b. When the eye is adducted, superior oblique directs the eye inferiorly and inferior oblique directs the eye superiorly.