Concussion Testing: What to Expect When Your MRI Is Normal

How Do Doctors Test for a Concussion?

A standard visit usually covers the history of the injury, a scored symptom checklist such as the SCAT, and a bedside neurological exam, often with a quick eye and balance screen such as the VOMS or the BESS. Concussion assessment tools are based mainly on what you report (Harris, 2022). A critical review of concussion assessment scales sorts the tools into 3 tiers: screening tests such as the SAC, the BESS and the King-Devick test; confirmatory tests such as the SCAT, ImPACT and the VOMS; and objective examinations such as physiologic markers, imaging studies and brain network analysis (Kaufman, 2021). If your workup so far has been questions, a symptom score and a scan, you've had the first 2 tiers. The third tier's physiologic markers are where something about your brain is measured instead of asked. This kind of testing is for symptoms that are still there after the first 7 to 14 days, whether that's weeks or years later.

Our team's starting point is that how your brain functions drives how you feel. If you're still having symptoms, there's a high likelihood that areas of your brain still aren't working the way they should. Finding them takes markers other than a scan.

Even the diagnostic criteria have disagreed with each other. When 178 adults with mild to moderate brain injuries were interviewed at the study's 3-month follow-up, the DSM-IV and ICD-10 definitions of post-concussion syndrome, the 2 criteria sets in use at the time, agreed only slightly on who had it, a kappa of 0.13, because fewer patients met the DSM-IV's cognitive deficit and clinical significance requirements (Boake, 2004). In our team's view, a label that 2 rulebooks couldn't agree on is a weak target for treatment, so a functional exam asks a different question: which systems have changed, and by how much.

Does an MRI or CT Show a Concussion?

Often it doesn't. CT is used in acute trauma care to exclude life-threatening lesions, and it's often normal in people with a mild traumatic brain injury, including those with persistent symptoms. Conventional MRI may pick up more, and many patients still show no clear abnormality despite ongoing clinical impairment (Jeong, 2026). Research sequences such as diffusion tensor imaging are being studied (Richter, 2024), and they aren't part of a routine scan.

A normal scan is still useful, because it rules out a life-threatening injury. It doesn't mean you've recovered. In the CENTER-TBI cohort, patients with a mild injury and a normal CT could have persistent symptoms for months to years (Richter, 2024). Why symptoms last that long is covered in do concussions heal on their own.

Our team's framing is that the hardware is usually pretty good, and what you can see are errors in the way things work. Those errors tell you which parts of the brain aren't doing their job.

1 published case shows what that looks like in practice. After a motor vehicle collision, a patient with persistent post-concussion syndrome had an unremarkable head CT and an unremarkable brain MRI, and a multimodal functional assessment found abnormalities across 8 domains, including infrared pupillometry, computerized dynamic posturography, saccadometry and 24-hour heart rate variability (Jay, 2026). It's 1 case, and it shows the gap a functional exam looks for: the structure was normal while 8 functional domains were off.

Why Aren't Symptom Checklists Enough?

A checklist measures what you report. The standard sport concussion tools are based mainly on subjective reports of physical, cognitive and emotional symptoms, those symptoms are underreported, and the authors of a meta-analysis of sideline tests wrote that objective measures of impairment would be valuable to assist diagnosis (Harris, 2022).

The same review found 8 studies in sport, all of the King-Devick test, a timed number-reading task, and pooled 4 of them: sensitivity 0.77, specificity 0.82, with the credibility of the evidence rated very low (Harris, 2022). In our team's reading, those numbers make it a screen. The King-Devick is itself a quick eye test, which is why the research our team leans on is recorded eye tracking (Snegireva, 2018).

Our team takes your symptoms as the starting point and then asks a second question: which systems are producing them. In our team's view, a symptom score, however carefully filled in, can't tell you that.

What Does a Functional Concussion Exam Measure?

A functional exam measures how well specific systems work, under conditions that load them. The table lists the tests a functional concussion exam can include and what the research says each can show after a concussion.

What a functional concussion exam measures

Test	What it measures	What it can show after a concussion	Page that explains it
Eye movements and gaze	Video oculography: infrared cameras record saccades, pursuit and how still the eyes hold a target.	Saccade and pursuit deficits that a clinical examination may miss, in acute concussion (Snegireva, 2018).	What part of the brain controls eye movements
Pupils	Infrared pupillometry: how fast and how far each pupil reacts to light.	A light reflex that is slower and smaller in both eyes (Ciuffreda, 2017).	Pupils different sizes after head injury
Balance	Balance with eyes closed and walking with a second task running: sway and walking speed.	Larger eyes-closed sway and slower gait more than 2 weeks out, past the point the sideline BESS calls recovered (Wood, 2019; Buckley, 2016).	Covered below
Autonomic reflexes	Heart rate and heart rate variability with posture and with exertion.	Changes that are clearer under exertion than at rest (Blake, 2016; Pathmanathan, 2025).	Autonomic testing
Blood flow and vision	The red saturation screen at the bedside, then Doppler ultrasound of the flow itself.	In the clinic's video, 1 patient (not described as concussed) had 1 eye dim when the head turned. No study has tested this screen after a concussion.	Post-concussion treatment at the clinic
Structural scan	CT and MRI: bleeding, lesions and structure.	Often nothing after a concussion, even with persistent symptoms (Jeong, 2026).	Covered above

Sources for the table: Snegireva 2018 (PMID 30523971), Ciuffreda 2017 (PMID 30202579), Wood 2019 (PMID 31219809), Buckley 2016 (PMID 30356901), Blake 2016 (PMID 26671602), Pathmanathan 2025 (PMID 40719257), Jeong 2026 (PMID 42111454). The blood flow row describes the clinic's bedside screen as shown in the video; its validity hasn't been studied.

Eye movements and gaze

Eye tracking measures how your eyes jump to a target (saccades), follow a moving one (pursuit) and hold still on one (gaze). In a meta-analysis of eye-tracking studies in sport concussion, people with an acute concussion differed from controls on all 7 variables compared, and the authors concluded that most saccadic and pursuit deficits may be missed during a clinical examination (Snegireva, 2018). The single variable compared in later concussions didn't differ, so the strongest evidence is early, and for people months or years out it's thinner. Our team uses goggles to record the eyes and to record them again after treatment, so the 2 recordings can be compared in the same person.

In our team's view, eye movements are the most direct window we have on function across the whole brain, because so many areas take part in holding and moving them, and healthy people have healthy eye movements. The circuits behind that, and the saccade and pursuit detail, are on what part of the brain controls eye movements.

Pupils

Infrared pupillometry records how each pupil reacts to a flash of light. After a mild traumatic brain injury the light reflex is delayed, slowed and reduced but symmetrical, the baseline pupil is smaller than in healthy people, and several pupil parameters separated people with light sensitivity from those without it (Ciuffreda, 2017). The word symmetrical matters: the change shows up in both pupils, which is a different finding from 1 pupil sitting larger than the other. Pupil size, the flashlight question and the emergency rules are on pupils different sizes after head injury.

Balance

Balance testing ranges from the sideline BESS, where you hold 3 stances with your eyes closed, on firm ground and on foam, while someone counts errors, to a force plate that records how your center of pressure sways. The difference matters once the first weeks have passed. In a meta-analysis of 22 studies, people tested more than 2 weeks after a concussion had a larger sway area with their eyes closed, and they walked 0.12 m/s slower on a single task and 0.06 m/s slower while doing a second task at the same time (Wood, 2019). The BESS has unacceptably low sensitivity and, repeated, can't accurately identify recovery, while instrumented measures of quiet stance and gait have found impairments well beyond BESS recovery, for at least 1 month after the injury (Buckley, 2016).

Autonomic reflexes

The autonomic nervous system sets your heart rate and blood pressure as you stand, breathe and exert yourself. A systematic review of 36 studies found that only 3 failed to find anomalies in autonomic measures after concussion, and concluded that concussion likely causes autonomic nervous system anomalies (Pertab, 2018). Where the changes show up is the practical point. The evidence on cardiac autonomic function at rest conflicts, while there's evidence of an elevated heart rate and reduced heart rate variability during low-intensity, steady-state exercise up to 10 days after a concussion (Blake, 2016), and a 2025 review in adolescents found mixed results, with possible cardiac autonomic dysfunction that was more apparent under exertion, and said methodological limits prevent firm conclusions (Pathmanathan, 2025). In children, the autonomic measure used most in the research is cardiovascular reflex testing with orthostatic stressors, and the results so far are mixed (Ramsay, 2026).

Put plainly, the evidence that concussion disturbs the autonomic system is consistent but low in quality, and the evidence for which bedside test to use is still early. In our team's exam that means heart rate and blood pressure are measured with posture and with effort, because a seated, resting reading can look normal. What each autonomic test measures is on autonomic testing, which is written for POTS; the tests are the same.

Blood flow and vision

The first major branch off the internal carotid artery, the main supply to the brain, is the ophthalmic artery, and it runs to the back of the eye: the left carotid feeds the left eye and the right carotid feeds the right. In our team's experience, when flow through that artery drops, the coloration or the intensity of vision changes in that eye. The red saturation test uses that. You cover 1 eye, then the other, look at the same red target and compare the hue, then repeat with your head turned. In eye care, a red difference between the 2 eyes is a classic sign of an optic nerve problem, which is 1 reason our team treats this as a bedside screen and checks the flow itself with Doppler ultrasound. The clinic adds 2 caveats of its own: a problem in the lens or the structure of the eye changes the result too, and the test isn't a way to diagnose yourself. The instruments used on the diagnostic day are listed on post-concussion treatment at the clinic.

Head neutral Head turned left

In 1 case our team saw (the video doesn't say it was a concussion), an artery on 1 side had audible turbulence and the radial pulse on that side was diminished. With the head facing forward everything looked normal, and with the head turned to the left the left eye went dark with black splotches. The finding was read as the head position compressing the artery, the rehab was aimed at taking pressure off it, and the symptoms dissipated. That's a single case, and it shows why the screen is run in several head positions.

What Does the Gaze Test Look Like in the Clinic?

You sit with a pair of goggles on. Inside them, infrared cameras watch each eye, and on a screen in front of you a single dot appears 15 degrees to the left. Your only job is to hold your eyes on it. Then the dot appears 15 degrees to the right and you do the same. The cameras record whether your eye oscillates, how fast, how big the movements are, how often they come, in which direction, and what your head is doing at the same time. The goggles record the shaking so it can be measured, and measured again after treatment to see whether anything changed.

The person in the video had been hurt 5 years earlier and was still having severe headaches, dizziness, trouble thinking, fatigue that needed naps during the day, irritability that was out of character, and blurry vision. Looking left, both eyes shook back and forth while trying to hold the dot. Looking right, the flickers came more often. Our team's reading of that finding is simple: if your eyes can't be still, the rest of your brain can't be still, because it's taking in the world through a moving picture.

Before 3 days later

Left target Right target

Replay

The treatment over the next 3 days used whole-body rotation in a mechanical chair to stimulate the inner ear, head and neck movements combined with eye tasks, shoulder work, and eye movements in different head positions. At the retest the left trace was almost still, and the right still had a little flicker, far less than 3 days before. His headache was gone, he wasn't dizzy or stumbling off the sidewalk, and he could think and get out and work. That's 1 person, with no numbers reported beyond what the traces show, so the case shows the pattern without proving it. Our team sees both courses: sometimes symptoms ease immediately once the eyes settle, and sometimes the brain keeps healing over weeks, the way a workout pays off with repetition.

In our team's exam, the blood flow check from the red saturation video sits beside the gaze test: listening over the carotid arteries, feeling the radial pulse, comparing the red target with your head in different positions, and then measuring the flow with Doppler ultrasound.

What Do the Results Change?

In our team's view, the point of testing is aim. Watching what the eyes do is a window into where in the brain things aren't working well, so treatment can be aimed there, and a retest tells whether the treatment is working. The case on camera is that logic: a test, a plan built on it, and a retest 3 days later.

Unsteady eyes put a huge tax on your brain, in our team's words, because energy goes into getting simple things right, and that makes complex tasks like reasoning, planning and thinking hard. Settling the eyes is where our team starts for that reason, and in our team's exam the other systems in the table are measured so the plan covers each system that's off.

What the research shows about the rehab for each of those systems is on post-concussion syndrome treatment, and how the testing day is arranged at the clinic is on post-concussion treatment at the clinic.

What Should You Bring and Ask?

Bring these:

• Your imaging reports, including the normal ones.
• A symptom list with what makes each one worse. Screens, standing, turning your head, exertion, noise, a full day at work. Our team uses the trigger to decide which system to test first.
• Prior test results. Eye exams, balance or vestibular testing, neuropsychological testing and any heart rate or blood pressure records.
• Your current medications and supplements. Ask your prescriber which of yours can change heart rate, pupils or balance.

Ask these:

• Which systems were measured, and which came back off?
• What were the numbers, and what would normal look like?
• What would a retest look like if the treatment is working?
• How does the plan change if it isn't?

What Happens After Testing?

In our team's practice the exam ends with a list of the systems that aren't doing their job, treatment is aimed at them, and a retest checks whether each system is changing. What the research shows about the rehab for each system is on post-concussion syndrome treatment. To book the diagnostic day at the clinic, start with post-concussion treatment at the clinic, and the 3D tour walks through the lab where the testing happens.

Concussion Testing: FAQ