Dilated Pupils and Concussion: What It Means and When to Worry

When someone suffers a concussion, one of the first things medical professionals check is the person’s pupils. Dilated pupils can be a sign of a head injury, but what does it really mean? How serious is it, and what should you do?

This guide explores the connection between dilated pupils and concussions, explaining what causes pupil changes, why doctors perform pupil exams, and when dilated pupils indicate a medical emergency.

Understanding Pupil Dilation

Your pupil is the black circle in the center of your eye that controls how much light enters. It constricts (gets smaller) in bright light and dilates (gets larger) in the dark.

Pupil size is influenced by several factors:

• Light: Pupils dilate in dim light and constrict in bright light.
• Stress or excitement: The body’s "fight-or-flight" response can cause pupils to widen due to an adrenaline release.
• Medications or substances: Some eye drops, stimulants, or recreational drugs can cause dilation.
• Injury or illness: Neurological conditions or injuries can affect the nerves controlling the pupil.

Normally, pupils are equal in size (about 2–4 mm in bright light, up to 8 mm in the dark) and react symmetrically to light. This reflex is a quick way to gauge if the brain’s autonomic and cranial nerve functions are intact.

What Is a Concussion?

A concussion is a mild traumatic brain injury (TBI) caused by a bump or jolt to the head. This sudden movement can cause the brain to move inside the skull, leading to chemical changes and temporary dysfunction of brain cells.

Key facts about concussions:

• They are serious injuries, even if often called "mild."
• Loss of consciousness is not required for a concussion to occur.
• Common symptoms include headache, confusion, dizziness, nausea, and sensitivity to light or noise.
• Rest is crucial for recovery.

Medical professionals check the pupils after a head injury to perform a quick neurological exam, often using the acronym PERRLA (Pupils Equal, Round, Reactive to Light and Accommodation). Any changes can provide critical clues about the severity of a brain injury.

Dilated Pupils and Concussions: The Connection

So, does a concussion cause dilated pupils? The answer is sometimes, but it's not a definitive sign.

• Mild concussions often do not cause noticeable pupil changes. Many people with a concussion have perfectly normal-looking pupils.
• Stress and adrenaline from the injury can temporarily widen the pupils. However, these pupils will still react to light and return to normal as the person calms down.
• Light sensitivity (photophobia) is a common concussion symptom. This can make a person prefer a dark room, which naturally causes their pupils to dilate. The key is that their pupils will still constrict when light is introduced.
• One pupil being larger than the other is a red flag. This is not a typical sign of a mild concussion and could signal a more severe problem like internal bleeding causing pressure on the brain.

Myth vs. Reality

The idea that dilated pupils are a guaranteed sign of a concussion is a myth, often perpetuated by movies. In reality, concussions are diagnosed based on a range of symptoms, not pupil size alone. Checking the pupils is vital because it helps rule out more severe brain injuries that can initially mimic a concussion.

"Anisocoria (unequal pupil sizes) following head trauma should be treated as an emergency until proven otherwise," note the Brain Trauma Foundation guidelines.

When Dilated Pupils Signal a Serious Problem

While a concussion is a mild TBI, a blow to the head can cause more severe injuries like brain bleeding (hematoma) or swelling. Abnormal pupil findings are a classic sign of these emergencies.

Seek immediate medical attention for these pupil-related signs:

• One pupil is dilated and the other is not (unequal pupils), especially if the larger pupil does not react to light. This can indicate pressure on a cranial nerve from bleeding or swelling.
• Both pupils are dilated and do not respond to light, particularly in an unconscious person. This is a grave sign of widespread brain damage.
• Both pupils are extremely constricted (pinpoint) and unresponsive, which can indicate certain brainstem injuries or a drug overdose.

If you see these signs after a head injury, call 911 immediately. These are life-threatening situations where time is critical.

Table: Concussion vs. Severe Brain Injury Signs

Feature	Concussion (Mild TBI)	Severe Brain Injury (e.g., Brain Bleed)
Pupil Size	Usually equal and reactive. May be slightly larger due to adrenaline but will still react to light.	Often unequal (one "blown" pupil) or both fixed and dilated. Unreactive to light.
Onset of Signs	Symptoms appear within minutes to hours. Pupil changes are not expected to worsen later.	A pupil may suddenly dilate minutes to hours after the injury as pressure builds.
Other Symptoms	Confusion, headache, dizziness, nausea, light/noise sensitivity. Loss of consciousness is brief or absent.	Worsening headache, repeated vomiting, declining level of consciousness, seizures, one-sided weakness.
Action	Seek medical evaluation. Requires rest and monitoring.	Medical emergency! Requires immediate hospitalization and possible surgery.

Other Visual Symptoms of Concussion

Even with normal pupils, a concussion can cause various other visual problems:

• Blurred or double vision (diplopia)
• Eye strain and fatigue, especially with reading
• Difficulty tracking moving objects
• Heightened sensitivity to light (photophobia)

These symptoms are usually temporary and improve with rest. If they persist, vision therapy from a neuro-optometrist may be helpful.

What To Do If You Suspect a Concussion

If you witness or experience a head injury, follow these steps:

1. Ensure Safety: Remove the person from any immediate danger (e.g., stop play in a sports game).
2. Check for Red Flags: Call 911 for severe symptoms like loss of consciousness, seizures, worsening headache, repeated vomiting, or unequal pupils.
3. Observe for Concussion Signs: Ask simple questions to check for confusion, assess balance, and note any other symptoms like headache or dizziness.
4. Monitor Closely: Symptoms can develop or worsen over 24-48 hours. Follow a doctor's advice on monitoring.
5. Seek Medical Evaluation: Anyone with a suspected concussion should be evaluated by a healthcare professional.
6. Do Not Return to High-Risk Activity: An athlete or worker should not return to play or their job on the same day. A second head injury before the first has healed can be extremely dangerous (second impact syndrome).

While a quick pupil check can be part of first aid, it is not a definitive test. A concussion can exist with perfectly normal pupils.

Treatment and Recovery

For a typical concussion, treatment focuses on physical and cognitive rest, followed by a gradual return to activities. Pupil size does not affect this recovery protocol.

However, if abnormal pupil signs were present, the patient would undergo urgent evaluation (like a CT scan) to rule out a brain bleed. The presence of a "blown pupil" shifts the focus from concussion management to emergency neurosurgical intervention.

Frequently Asked Questions (FAQ)

Q: Do dilated pupils always mean a concussion has occurred? A: No. Pupils can dilate due to darkness, adrenaline (stress/fear), or other factors. Many people with concussions have normal-sized, reactive pupils. While dilated pupils can occur with a concussion, the sign by itself isn’t enough for a diagnosis. Conversely, you can have a concussion even if your pupils are not dilated.

Q: If someone has a concussion, will their pupils be different sizes? A: Typically no. In a straightforward concussion, pupils are generally equal in size and reactive. If someone’s pupils are noticeably different sizes after a head injury (anisocoria), it should be treated as a potential emergency, as it could indicate a more serious brain injury like internal bleeding.

Q: How long do pupils stay dilated after a concussion? A: In most concussions, any pupil dilation related to stress or adrenaline is temporary and resolves as the person calms down. There is no prolonged, noticeable pupil dilation from a simple concussion. Persistent dilated pupils, especially if they don’t react to light, would signal a more severe or worsening brain issue requiring immediate medical attention.

Q: Should I use a flashlight to check my child’s pupils if I suspect a concussion? A: As a first-aid step, a single, quick pupil check can be reasonable if done gently. However, do not rely on a home exam to rule out a concussion. Even if pupils seem normal, the child should be monitored for other symptoms and evaluated by a healthcare provider. If pupils are unequal or unreactive, seek emergency care immediately.

Q: Can anything else cause one pupil to dilate besides a brain injury? A: Yes. Unequal pupils can be caused by direct eye injuries, certain medications or eye drops, migraines, or congenital conditions like physiological anisocoria. However, in the context of a head injury, a new onset of unequal pupils should always be treated as a potential sign of serious brain trauma.

Q: Can a concussion cause permanent pupil changes? A: A simple concussion is very unlikely to cause permanent changes to pupil size or reactivity. Permanent changes usually result from more severe nerve damage, direct trauma to the eye itself, or a severe TBI that damages cranial nerve pathways. Once the brain recovers from a concussion, the autonomic control of the pupils should return to normal.

Expert Insight

“If one pupil is larger than the other after a head injury, that’s a big red flag. It usually suggests a more serious issue like bleeding in the brain, not just a concussion. That person needs to be in the ER immediately. In a routine concussion, the pupils are typically equal and reactive.” — Dr. Mark Halstead, sports medicine physician

“We always say: When in doubt, sit them out. No game or practice is worth risking a second head injury. Whether or not their pupils look dilated, if a player shows any concussion signs, they’re done for the day. I’ve seen plenty of concussions with normal pupils. That doesn’t mean the athlete is okay to continue.” — Jane McDevitt, certified athletic trainer

Prevention Tips

The best way to treat a concussion is to prevent it.

• Wear appropriate helmets for sports, biking, and other high-risk activities.
• Always use seatbelts and properly installed child safety seats in vehicles.
• Make living areas safer to prevent falls, especially for children and older adults.
• Follow safety rules in sports to minimize dangerous plays.

Conclusion

While dilated pupils can be a clue after a head injury, they are just one piece of the puzzle.

• Most concussions involve normal pupils. Don't rule out a concussion just because pupils look fine.
• Unequal or unreactive pupils are a medical emergency. This is a red flag for a severe brain injury and requires immediate medical attention.
• Always prioritize safety. When in doubt about a head injury, seek a medical evaluation and ensure the brain has adequate time to heal before returning to high-risk activities.

Understanding the role of pupil evaluation and recognizing the broader symptoms of concussion can help you respond safely and effectively.

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Resources & Further Reading:

• CDC: Concussion Signs and Symptoms – An overview from the Centers for Disease Control and Prevention on concussion indicators and emergency danger signs. cdc.gov/headsup
• Mayo Clinic: Concussion – Detailed information on concussion symptoms, causes, and when to see a doctor. mayoclinic.org
• BrainLine: Vision Problems after TBI – An article discussing how traumatic brain injuries can affect vision and treatment options. brainline.org
• Concussion Recognition Tool 5 (CRT5) – A guide from the Concussion in Sport Group to help non-medical personnel identify possible concussions. bjsm.bmj.com

Disclaimer: This article is for informational purposes only and is not a substitute for professional medical advice. If you suspect a concussion or any head injury, consult a qualified healthcare provider.