After the Hit: Understanding Concussion and Your Vision
You didn’t lose consciousness. The scans look normal, and you are told that you should be ‘fine in a few weeks’. Yet weeks — or months — later, you still can’t read a page without your eyes hurting, crowds make you feel sick, bright lights are unbearable, and you can’t concentrate the way you used to. You start to wonder if it’s all in your head.
In a way, it is — but not the way you might think. Concussion is a genuine brain injury, and the visual system is one of the most commonly affected areas of the brain following a head knock. This blog explains what concussion actually does to your brain and vision, why standard medical tests so often miss the damage, and what an appropriately trained optometrist can do to help you recover.
What Is a Concussion?
Concussion is classified medically as a mild Acquired Brain Injury (mABI) or mild Traumatic Brain Injury (mTBI). These terms are used interchangeably in both clinical and research settings. It sits at the less severe end of the traumatic brain injury spectrum, but ‘mild’ does not mean insignificant.
Concussions can result from a wide range of incidents, including:
Falls and workplace injuries
Sports-related head knocks (football, cycling, martial arts, equestrian sports)
Motor vehicle accidents
Assaults
Blast or explosion injuries
Critically, you do not have to lose consciousness to sustain a concussion. Many people are concussed without ever “blacking out”, and some do not experience symptoms immediately — symptoms can emerge hours after the event. This delayed onset is well documented in the literature, and it’s why early and appropriate assessment matters so much.
It is also worth knowing that females, on average, sustain concussions more readily and experience longer-lasting symptoms than males in comparable sporting situations. Factors such as thinner skulls, less neck musculature, hormonal differences, and fewer years of experience absorbing contact all contribute to this difference (Wunderle et al., 2014).
What Happens Inside the Brain After a Concussion?
Concussion causes a complex neurometabolic cascade — a chain of biochemical events that disrupts normal brain function. The force of injury stretches and shears the delicate axons (nerve fibres) and cell membranes of neurons, especially at the junction between the brain’s white and grey matter.
This triggers the following sequence:
An initial excitatory phase, during which neurons fire abnormally, and ion balance is disrupted.
A depressive phase follows, during which brain activity is suppressed.
The brain’s sodium-potassium pump works overtime to restore balance, rapidly depleting the brain’s energy supply (ATP).
Elevated calcium levels disrupt mitochondrial function, forcing the brain to switch to a less efficient form of energy production (anaerobic glycolysis), which is approximately nine times less efficient.
The result is a profound brain energy crisis: energy demand far outstrips supply (Barkhoudarian, Hovda & Giza, 2011).
This energy crisis, combined with physical damage including micro-vessel bleeding, cell wall rupture, glia injury, and axonal shearing, underpins the wide range of symptoms concussion sufferers experience.
Common symptoms include:
Persistent headaches, often made worse by exercise or concentration
Poor concentration and memory difficulties
Easy mental and physical fatigue
Irritability and mood disturbances
Intolerance to light and sound
Anxiety, depression, and sleep disturbance
Visual disturbances: blurred vision, double vision, difficulty reading, sensitivity to light and movement
“But My Scan Was Normal” — Why Standard Eye Tests Miss Concussion
One of the most distressing experiences for concussion sufferers is being told that their CT or MRI scan is ‘clear’ yet continuing to experience significant symptoms. Standard CT and MRI scans are designed to detect structural abnormalities such as fractures, bleeds, or tumours. They are almost always normal in concussion patients, because the damage is functional and metabolic rather than grossly structural.
More sophisticated imaging such as functional MRI (fMRI) does reveal abnormalities in neural network activity. Research demonstrates altered activity in the networks responsible for eye movement control, reading comprehension, spatial localisation, navigation, and spatial working memory — all systems critical for daily functioning (Rockswold et al., 2019).
Importantly, a 2025 study of 28 patients with chronic concussion and normal visual acuity found that 64% reported ongoing vision problems and 68% were light-sensitive. Sophisticated analysis also identified subtle changes along the primary visual pathway, including in the optic radiations and occipital lobe, changes that ordinary scans would miss entirely (Rasdall et al., 2025).
If your scan is normal but your symptoms are real, please know you are not imagining it. The damage is real. It is simply occurring at a level of detail that standard imaging cannot detect.
How Common Are Visual Problems After Concussion?
The visual system is particularly vulnerable to concussion because it relies on such a vast proportion of the brain’s processing resources. The sheer extent of vision-related brain circuitry means that almost any concussion will disrupt some aspect of visual function.
Research comparing concussed individuals with healthy controls has found striking differences (Capo-Aponte et al., 2012):
Convergence insufficiency (difficulty pointing both eyes inward at a near object): 55% of concussed patients vs 5% of controls
Pursuit impairment (difficulty smoothly tracking a moving object, or lines of text): 60% vs close to 0%
Accommodative dysfunction (difficulty focusing): 65% vs 15%
Vertical eye misalignment: 55% vs 5%
Saccadic impairment (difficulty making rapid, accurate eye movements): 30% vs close to 0%
A separate study found that 76% of post-concussion patients had accommodative insufficiency (difficulty adjusting focus) and 56% had convergence insufficiency. Reduced reading rate was present in 82% and reduced reading efficiency in 68% (Tannen et al., 2015). These are not trivial problems — they profoundly affect your ability to work, study, drive, and manage daily life.
For context, convergence insufficiency occurs in only around 4% of the general population and accommodation dysfunction in around 6% — the concussion-related rates are many times higher.
The Specific Visual Conditions You May Experience After a Concussion
Accommodation Dysfunction
Accommodation is your eye’s ability to change focus between distances, such as shifting your gaze from your phone to the television. Following concussion, this system is frequently disrupted. You may experience blurred vision at near, difficulty sustaining reading, eye fatigue, and headaches after visual tasks. This is the most commonly affected visual function after acquired brain injury, yet it is rarely identified by non-optometric clinicians.
Convergence Insufficiency
Convergence is the ability to turn both eyes inward simultaneously to maintain single, clear binocular vision at close range. When this system is compromised, reading becomes an exhausting struggle. Words may blur, double, or appear to move on the page. Reading speed slows dramatically, comprehension drops, and the effort required often triggers headaches and nausea.
Photophobia and Pattern Glare
Many concussion patients become highly sensitive to light. It is important to distinguish between two related but distinct conditions:
Photophobia: increased sensitivity to light, particularly outdoors, while remaining relatively comfortable indoors.
Pattern glare: significantly increased sensitivity to both indoor and outdoor light, accompanied by discomfort from repetitive visual patterns — such as striped clothing, patterned carpets, fluorescent lighting, venetian blinds, and even lines of small print.
Lines of standard reading print (approximately 12–14-point font) are, in effect, alternating light and dark stripes, and can trigger blurring, movement, or distortion of text. Flickering light sources such as fluorescent office lighting, driving under streetlights, or scrolling text on screens can be profoundly disabling.
The severity of photosensitivity is influenced by multiple factors: the number of concussions sustained, anxiety, sleep disturbance, the time elapsed since injury, dry eye, and certain medications (Jotie et al., 2024).
Visual Motion Hypersensitivity (VMH)
Also referred to as visual vertigo or visually induced dizziness, VMH occurs when the visual, vestibular (balance), and somatosensory (body position) systems fail to communicate accurately. After a concussion, the brain struggles to integrate information from these three systems, resulting in an overwhelming and often disabling mismatch (Petrosyan, 2019).
You may recognise VMH in yourself if you experience:
Nausea, dizziness, or vertigo in busy environments such as shopping centres, crowded areas, or sporting venues
Feeling as though the car is still moving after stopping at traffic lights
Supermarket aisle shelves appearing to move as you walk past them
Feeling better as the driver of a vehicle than as a passenger
Nausea from scrolling on a phone or computer screen
Discomfort from escalators, lifts with windows, and fast-moving images on television
Palinopsia
A less well-known but genuinely distressing symptom is palinopsia — the persistent recurrence of a visual image either while it is still moving, or after it has been removed from view. A ball in flight may leave a trail of ghost images; a car passing by may leave a visual echo. This is thought to be related to disruption of eye movement and visual input processing in the brain.
Recovery: What to Expect
Research suggests that 80–90% of people who sustain a concussion will recover spontaneously, generally within two weeks for adults and four weeks for children and adolescents, according to the Berlin Concussion Guidelines. However, 10–20% of concussion sufferers develop what is known as post-concussion syndrome — a prolonged period of symptoms that can last months or years.
A critical warning: secondary concussion occurring within 12 months of the first carries a five-to-six-fold increased risk compared to a person who has not been concussed. Each additional concussion compounds the cumulative risk of long-term brain and vision complications. This is why appropriate management, including being removed from sport and avoiding premature return to full activity, is so important — even if it feels frustrating in the short term.
If your symptoms are persisting beyond a month, or are significantly affecting your quality of life, work capacity, or study, waiting and hoping they resolve on their own is not a sound strategy. Early optometric assessment has been shown to contribute meaningfully to recovery outcomes.
How Can an Optometrist Help?
Optometrists trained in neuro-optometric rehabilitation offer a level of assessment and management that goes far beyond what is available in a standard eye examination. A comprehensive assessment for concussion-related visual dysfunction will typically cover specific levels of care (Ciuffreda et al., 2015):
Standard vision examination: refraction, basic accommodation, ocular motility, and health.
Oculomotor assessment: comprehensive binocularity, accommodation, vergence, eye movement, and vestibular interaction testing.
Non-oculomotor visual assessment: photosensitivity, pattern glare, visual motion hypersensitivity.
Non-visual issues: anxiety, depression, cognitive impairment, and migraine may also be present. These non-visual issues interact with and may compound visual symptoms.
Even apparently minor refractive errors (such as a small amount of long-sightedness that the brain previously compensated for easily) can become significantly decompensated after concussion. Many patients present complaining of blurred vision despite wearing their existing glasses, or despite being told their vision is ‘6/6’ (20/20). This is because central vision quality depends on stable peripheral visual processing — and it is that stability which concussion disrupts.
What treatments are available?
Corrective lenses: Updated glasses or low-powered reading additions can make an immediate and meaningful difference to comfort and function.
Prism lenses: Used to reduce the effort required for binocular vision when eye alignment is disrupted.
Precision chromatic filters (tinted lenses): Individually prescribed colour filters can substantially reduce pattern glare and visual motion sensitivity. The optimal colour varies from person to person and is determined using a specialised instrument called the Intuitive Colorimeter. Wraparound spectacle styles can additionally reduce discomfort from peripheral movement.
Vision therapy: A structured programme of in-office and home-based exercises designed to retrain the visual and visuomotor systems.
OCT imaging and contrast sensitivity testing: Advanced investigations that can reveal subtle changes in optic nerve fibre layer thickness and visual processing not detectable by standard examination.
What Does the Evidence Say About Treatment?
The evidence base for optometric intervention in concussion is growing rapidly and is now compelling. Of particular significance is the landmark CONCUSS randomised clinical trial (Alvarez, Scheiman et al., 2025), which provides the highest level of clinical evidence available:
In-office sequential vision therapy for post-concussion convergence insufficiency was found to be highly effective.
Watchful waiting (simply hoping symptoms resolve) did not produce equivalent improvement.
Importantly, pencil push-up exercises performed at home were no better than a placebo. Effective vision therapy is a clinical procedure, not a set of exercises you can simply look up online.
Companion fMRI neuroimaging data from the same clinical trial showed that vergence and accommodative rehabilitation produced measurable changes in the brain networks that support binocular vision and eye teaming (Sangoi et al., 2025). This is direct evidence that vision therapy is not just symptom management — it is driving neurological recovery.
Current evidence also supports a broader multidisciplinary approach to concussion management, in which optometrists trained in neuro-optometric rehabilitation serve as a critical component of the care team (Baxstrom, 2016). Including optometric assessment in the recovery team has been shown to improve outcomes for patients with both visual and vestibular symptoms.
Accommodation and convergence dysfunctions, even when severe or long standing, can often be substantially normalised with the appropriate combination of lenses, prisms, and vision therapy. Treatment makes a meaningful difference to reading, rehabilitation progress, and quality of life.
Finding the Right Optometrist
Not all optometrists have specialist training in neuro-optometric rehabilitation.
Adrian Rossiter is an ACBO Fellow and has completed The Australasian College of Behavioural Optometrists (ACBO) Accreditation in Neuro-Optometric Care (ANOC) programme, which involves an extensive program of neuro-optometric education.
There are currently around 90 accredited optometrists across Australia and New Zealand who have completed this programme. If your symptoms are persisting beyond one month, or are significantly affecting your daily life, ask for a referral to one of these practitioners, or ask your current optometrist to refer you.
A directory of practitioners can be found at: https://www.acbo.org.au/for-patients/about-vision/336-neuro-optometric-care
Practical Tips While You Seek Assessment
While you are waiting for your optometric appointment, or working through the early stages of management, the following strategies may help reduce visual discomfort:
Reduce screen brightness to the lowest comfortable level.
Switch your screen to a dark mode (white text on dark background) to reduce the ‘striped’ effect of print.
Increase text size on screens to increase the gap between lines of text.
Print documents rather than reading from a screen where possible.
Avoid fluorescent lighting in favour of warm incandescent alternatives where possible.
Wear wraparound sunglasses outdoors to reduce peripheral light exposure and movement.
Avoid scrolling rapidly on phones or computers, and limit exposure to fast-moving imagery on television.
Conclusion
Concussion is a real brain injury. Its effects on the visual system are extremely common, often profound, and frequently unrecognised by the broader healthcare system. If you are struggling with visual symptoms after a head knock — whether that was last month or last year — you deserve a thorough assessment by someone with the training to identify and treat what is happening.
The good news is that with appropriate assessment and evidence-based management, many of these conditions can be significantly improved. You do not need to simply endure them. A normal scan does not mean a normal brain, and a normal brain does not mean a normal visual system. Seek out the right expertise and give your recovery the attention it deserves.
References
Ciuffreda, K.J., et al. (2016). Traumatic Brain Injury: Visual Consequences, Diagnosis and Treatment. In Advances in Ophthalmology and Optometry. Elsevier, Philadelphia, pp. 307–333.
McCrory, P., et al. (2017). Consensus Statement on Concussion in Sport — the 5th International Conference on Concussion in Sport Held in Berlin, October 2016. British Journal of Sports Medicine, 51(11), 838–847.
Petrosyan, T. (2019). What Is Visual Motion Hypersensitivity? Visual Development & Rehabilitation, 5, 8–13.
Rasdall, M.A., et al. (2025). Primary Visual Pathway Changes in Individuals With Chronic Mild Traumatic Brain Injury. JAMA Ophthalmology, 143, 33–42.
Rockswold, S.B., et al. (2019). Functional Magnetic Resonance Imaging and Oculomotor Dysfunction in Mild Traumatic Brain Injury. Journal of Neurotrauma, 36(7), 1099–1105.
Sangoi, A., et al. (2025). Functional Activity Changes After Vergence and Accommodative Rehabilitation of Concussion-Related Convergence Insufficiency: CONCUSS Clinical Trial fMRI Results. Frontiers in Neuroscience, 19, 1303781.
Tannen, B., et al. (2015). Vision and Reading Deficits in Post-Concussion Patients: A Retrospective Analysis. Visual Development & Rehabilitation, 1, 206–213.
Wunderle, K., et al. (2014). Menstrual Phase as Predictor of Outcome After Mild Traumatic Brain Injury in Women. Journal of Head Trauma Rehabilitation, 29, E1.
This blog was prepared drawing on the WAVE 2026 presentation ‘Concussion = mild acquired brain injury (mABI)’ by Steve Leslie, B Optom FACBO FCOVD Dip Cert Oc Ther Spec Cert MNOD, and cited peer-reviewed literature. It is intended as general health information only and does not constitute optometric or medical advice. Please consult a qualified health professional for individual assessment and management.
