Emergency Medical Technician (EMT) Intermediate Practice Exam

What does a dilated and unreactive pupil in a head injury patient indicate?

1. Increased intracranial pressure

2. Pressure on the optic nerve

3. Pressure on the oculomotor nerve

4. Brain stem injury

The correct answer is: Pressure on the oculomotor nerve

A dilated and unreactive pupil in a patient with a head injury strongly indicates pressure on the oculomotor nerve. The oculomotor nerve is responsible for controlling pupil constriction as well as several eye movements. When there is an increase in intracranial pressure, such as from swelling or a mass effect (like bleeding), it can lead to pressure exerted on the nerve itself. This pressure impairs the nerve's ability to function properly, resulting in pupil dilation since the constrictor muscle, which is normally activated by the oculomotor nerve, cannot operate. Consequently, the pupil fails to react to light, meaning it remains dilated and unresponsive. This symptom serves as a critical indicator in the assessment of brain injuries, as it can point towards serious underlying conditions including potential herniation or other life-threatening issues. In this context, while increased intracranial pressure may lead to various symptoms and findings, the direct implication of pupil dilation is more specifically linked to the impact on the oculomotor nerve rather than just an overall increase in pressure or damage elsewhere in the brain.