Spotting early pupil changes after a head knock can guide you toward the right care faster than any phone app. This walk‑through shows how to check for concussion pupils safely at home or pitch‑side, then flags the red‑alert signs that call for professional help.
Fast Reference Table
| What You Notice | Flashlight Response | Likely Meaning |
|---|---|---|
| Both pupils equal & shrink briskly | <1 sec constriction | Typical finding |
| Unequal pupils >1 mm apart | Sluggish or fixed in one eye | Possible cranial nerve III issue or raised pressure |
| Both pupils wide & slow | >2 sec constriction | Autonomic disruption, drug effect, or swelling |
Why Pupils Matter After A Head Knock
The black center of the eye works like a camera aperture. A healthy brain keeps both sides equal and quick to light. When trauma bruises neural pathways, one of the first signs can be an asymmetry called anisocoria. A simple torch test often spots trouble before scans or apps load, which is why field medics still reach for a penlight first.
Safety Prep Comes First
1. Make sure the scene is safe.
2. Ask the person to sit or lie still to avoid sudden drops in blood pressure.
3. Wash or sanitize your hands, then grab a low‑beam flashlight and a watch with seconds.
4. Dim surrounding lights if possible; pupils react best against a low ambient background.
5. Tell the person you’ll shine a light so they won’t flinch.
Supply Checklist
- Penlight or phone torch set to low
- Timer
- Notebook or phone note to record findings
- Dark card or hand to block the other eye
Step‑By‑Step Pupil Exam
1. Observe At Rest
Stand in front and note baseline size in each eye. Equal diameters (usually 2‑4 mm in room light) are reassuring.
2. Swing The Light
Hold the light 4 inches from the outer edge of the right eye, then sweep inward across the pupil. It should snap smaller within a second. Repeat on the left.
3. Measure Speed
Count how long constriction takes. Anything slower than two seconds or that shows a “dampened” movement needs note.
4. Look For Re‑Dilation
After removing the light, the pupil should enlarge at a steady pace. A pupil that stays small or bounces can signify brainstem irritation.
5. Block One Eye
Cover the left eye, shine into the right, and watch the covered pupil through a gap in your fingers. Both pupils should react together. Lack of a paired response suggests pathway disruption.
6. Compare Sizes Again
If one pupil now looks >1 mm larger, write it down, then re‑check in five minutes. Persistent or widening asymmetry calls for medical review.
When To Call A Clinician Fast
Dial emergency services if you see:
- Unequal pupils that stay different for ten minutes
- No reaction to light in either eye
- Rapidly widening one‑sided pupil
- Severe headache, repeated vomiting, or seizure along with eye findings
NHS trauma guidance lists these signs as reasons to seek hospital care without delay. NHS head injury advice.
The CDC TBI portal states that uneven pupils warrant immediate evaluation because they can mark rising intracranial pressure.
Factors That Skew The Test
Medications & Eye Drops
Many allergy drops, antidepressants, or recreational substances alter pupil width. Ask about recent use before you panic.
Lighting Conditions
Bright sunlight shrinks pupils, while a dark locker room makes them larger. Always dim overhead lamps so your penlight stands out.
Contact Lenses Or Eye Trauma
A scratched cornea can make someone squint or tear, hiding true pupil size. Remove tinted contacts if safe, and rinse debris gently.
Tracking Changes Over Time
Pupils can worsen hours after impact, which is why many clinics repeat checks through the night. Parents may be told to wake children every two hours and shine a dim light.
Pupil Checks At A Glance
| Time Post‑Injury | What To Record | Next Step |
|---|---|---|
| 0–30 min | Baseline size & light reflex | Document in note app |
| 2 hr | Repeat test; note any drift | If new asymmetry → urgent care |
| Overnight | Check once if symptoms wake them | Stable? Resume normal sleep |
Myth‑Busting Corner
- “Dilated pupils always mean a concussion.” Not true. Fear, cold meds, or dark rooms widen pupils too.
- “You must wake someone every hour.” Modern NIH TBI advice focuses on worsening signs, not rote alarms.
- “If the eyes look normal, the brain is fine.” Mild concussions can hide; rely on a full symptom checklist as well.
Practical Tips For Clear Results
Keep the torch beam narrow; a broad phone flash can wash both eyes. Hold steady for one second only, since prolonged light fatigues muscles. Have a friend film the test so you can replay in slow motion and spot subtleties. Use an index card to shield the opposite eye when rooms are bright.
Quick Symptom Pairings
Combine pupil findings with these self‑reported cues to build a fuller picture:
- Blurry vision or double lines
- Ringing ears
- Balance wobble
- Nausea surge after movement
Delayed light response plus two of the above raises suspicion for mild traumatic brain injury, even if scans appear normal early on.
Wrap‑Up & Next Steps
A quick, well‑lit pupil test can steer you toward faster care and peace of mind. Follow the steps, track changes, and trust your gut. If anything feels off, head for trained evaluation—eyes rarely lie about the brain behind them.