Question

you are closely observing a patient admitted to the icu for head trauma. during his last examination, the patient demonstrated normal gaze. now the patients left eye is deviated inward, and he complains of double vision. what is your concern?

the trochlear nerve is not functioning properly.

the facial nerve is not functioning properly.

the oculomotor nerve is not functioning properly.

the abducens nerve (cranial nerve vi) is not functioning, possibly because of increased pressure inside the cranium. this is a crucial diagnostic clue.

Explanation:

1. Recall the functions of cranial nerves related to eye movement:

• Trochlear nerve (IV): Primarily for eye downward and inward movement, but deviation here is inward with double vision, and trochlear issue usually causes different deviation patterns.
• Facial nerve (VII): Controls facial muscles, not eye movement, so this is irrelevant.
• Oculomotor nerve (III): Controls most eye movements, but inward deviation with double vision and the context of head trauma (possible increased intracranial pressure) points more to abducens.
• Abducens nerve (VI): Controls lateral (outward) eye movement. If it's not functioning, the eye deviates inward (due to unopposed medial rectus muscle, controlled by oculomotor nerve). Head trauma can lead to increased intracranial pressure, which can compress the abducens nerve (it has a long intracranial course, making it vulnerable to pressure changes). Double vision (diplopia) occurs because the eyes are not aligned.

1. Evaluate each option:

• Trochlear nerve issue: Incorrect deviation pattern.
• Facial nerve: Not related to eye movement.
• Oculomotor nerve: While it controls eye movement, the specific deviation (inward with double vision in head trauma context) and the vulnerability of abducens to pressure make this less likely.
• Abducens nerve: Matches the deviation (inward, as it can't move outward), double vision, and the context of head trauma (possible increased intracranial pressure) which is a crucial diagnostic clue.

Answer:

The abducens nerve (cranial nerve VI) is not functioning, possibly because of increased pressure inside the cranium. This is a crucial diagnostic clue.