Loss of conjugate movement when looking to the left in the six cardinal directions of gaze suggests damage to which cranial nerve?

Loss of conjugate movement when looking to the left in the six cardinal directions of gaze suggests damage to which cranial nerve?

• A. Cranial Nerve II (CN II)
• B. Cranial Nerve IV (CN IV)
• C. Cranial Nerve V (CN V)
• D. Cranial Nerve VII (CN VII)

Answer: (B)

Focus on how the six cardinal directions of gaze are produced by the eye muscles and their nerves. When you look to the left, the left eye must abduct and the right eye must adduct. The eye that adducts (the right eye in this leftward gaze) relies on the medial rectus for adduction and on the superior oblique muscle to help position and depress the eye appropriately as it moves into adduction. The superior oblique is controlled by the trochlear nerve. If the trochlear nerve is damaged, the superior oblique doesn’t function properly, so the adducting eye cannot move smoothly and in sync with the abducting eye. This disruption leads to a loss of conjugate movement when looking left.

Focus on how the six cardinal directions of gaze are produced by the eye muscles and their nerves. When you look to the left, the left eye must abduct and the right eye must adduct. The eye that adducts (the right eye in this leftward gaze) relies on the medial rectus for adduction and on the superior oblique muscle to help position and depress the eye appropriately as it moves into adduction. The superior oblique is controlled by the trochlear nerve. If the trochlear nerve is damaged, the superior oblique doesn’t function properly, so the adducting eye cannot move smoothly and in sync with the abducting eye. This disruption leads to a loss of conjugate movement when looking left.