What is the flashlight test for concussion?

The Flashlight Test: A Quick Check for Concussion

When a head injury occurs, one of the fastest ways to assess potential concussion is the flashlight test—a simple but telling method used by trainers, paramedics, and medical professionals alike. While not a definitive diagnosis, it offers immediate insight into brain function following trauma.

The test involves shining a low-beam flashlight from the outer edge of each eye toward the nose. In a healthy individual, the pupils should quickly constrict—get smaller—as they react to the light. This reflex, known as the pupillary light response, is controlled by the brainstem and is usually prompt and symmetrical in both eyes.

However, a slow or uneven response can signal trouble. If one or both pupils react sluggishly to light, it may indicate increased intracranial pressure (ICP)—a dangerous buildup of pressure inside the skull that can follow a concussion or more severe brain injury. In some cases, one pupil may even appear larger than the other, a sign called anisocoria, which also raises red flags.

It's important to remember that the flashlight test is just one piece of the puzzle. A person can have a concussion without abnormal pupil responses, and not all delayed reactions mean serious injury. But when combined with symptoms like confusion, dizziness, nausea, or loss of consciousness, an abnormal test strengthens the need for immediate medical evaluation.

While this quick assessment isn’t a substitute for professional care, it’s a valuable tool in sports sidelines, emergency settings, or even at home when used wisely. If in doubt after a head impact, always err on the side of caution—seek medical help without delay.