A concussion, medically known as a mild traumatic brain injury, is caused by a blow to the head or body that results in a temporary change in normal brain function. This injury disrupts the brain’s internal signaling and communication pathways rather than causing major structural damage visible on standard imaging. Since the brain heavily processes visual information and controls eye movement, up to 90% of people who sustain a concussion experience visual or ocular dysfunction. Observable changes in the eyes offer reliable, immediate indicators of a potential injury, guiding prompt action.
Disrupted Eye Movement and Alignment
A common consequence of a concussion is the brain’s impaired ability to coordinate the muscles that control the eyes, leading to difficulties with eye movement and alignment. A specific sign is nystagmus, which appears as repetitive, uncontrolled, and rapid eye movements. This is particularly noticeable when the eyes attempt to track a moving object or look far to one side, reflecting instability in the brain’s gaze-stabilizing systems.
Another disruption is saccadic dysfunction, where the eyes struggle to make quick, accurate jumps from one fixed point to another. This difficulty manifests as the person frequently losing their place while reading or being unable to smoothly shift their gaze between two stationary targets. When following a moving target (smooth pursuit), the eyes may track the object in a jerky or hesitant manner instead of a continuous, fluid motion.
A further observable sign is convergence insufficiency, occurring when the eyes cannot effectively turn inward to focus on a close object. When focusing on something nearby, one or both eyes may visibly drift outward, indicating poor eye teaming. This muscular inefficiency strains the visual system and is a hallmark of post-concussion visual problems. This lack of coordination causes the brain to receive conflicting visual information, resulting in symptoms like double vision and eye fatigue.
Pupil Response and Light Sensitivity
Disruption to the autonomic nervous system frequently affects the eyes and is observed in the pupils’ reaction to light. Pupils normally constrict quickly and equally in response to a light source, but following a concussion, they may exhibit a sluggish or minimal reaction. This slow response, or failure to constrict fully, is a physical sign of neurological compromise.
It is possible to observe anisocoria, where one pupil appears noticeably larger than the other, indicating an irregularity in the nerve signals controlling pupil size. Because the brain’s ability to process visual data is compromised, the autonomic nervous system may become dysregulated. This can cause pupils to dilate more than they should in normal ambient light, allowing excessive light to enter and overload the visual pathways.
This overstimulation is the underlying mechanism for photophobia, or extreme sensitivity to light, a common complaint after a concussion. The person may react strongly to normal light levels, such as fluorescent indoor lighting or sunlight, by squinting, wearing sunglasses indoors, or actively shielding their eyes. This visible behavior indicates an underlying issue with the brain’s ability to manage visual input.
Subjective Visual Disturbances
A person with a concussion often reports changes in visual perception that can be inferred from their behavior, beyond the physical mechanics of the eyes. One common complaint is diplopia, or double vision, where the person sees two distinct images of a single object because their eyes are not aligning properly. This symptom can lead to difficulties with balance and coordination.
Blurred vision is another frequent subjective symptom, where sight is hazy or out of focus, often due to an inability to sustain focus. The person may be seen rubbing their eyes or trying to blink away the blurriness, especially during tasks requiring close attention. They may also report significant visual fatigue, noting that their eyes feel strained after only a short period of visual work, such as looking at a computer screen.
The person may exhibit signs of issues with visual processing speed, showing difficulty in scanning a complex environment or navigating a crowded space. They may bump into objects or appear clumsy, which traces back to problems with depth perception or an inability to process visual information quickly. These behavioral changes are a consequence of the visual system’s post-concussion dysfunction.
Immediate Steps After Identifying Eye Symptoms
Observing any unusual eye movement, pupil asymmetry, or significant light sensitivity following head trauma requires an immediate protocol for safety and medical evaluation. The first step is to remove the person from any activity that carries a risk of further injury and ensure they are resting physically and cognitively. While a medical professional should evaluate all suspected concussions, the presence of certain “Red Flag” symptoms requires an immediate call to emergency services.
Anisocoria (one pupil being significantly larger than the other) is a specific red flag that may indicate a severe, expanding brain injury requiring urgent intervention. Other severe symptoms demanding emergency care include seizure or convulsion, slurred speech, or increasing confusion or drowsiness. A headache that rapidly worsens or repeated vomiting are serious signs that necessitate an emergency room visit.
If no immediate emergency signs are present, the person should still be seen by a healthcare provider trained in concussion management within 24 to 48 hours. During this initial period, management should focus on relative rest, meaning the person should avoid activities that worsen their symptoms, such as reducing screen time and demanding visual tasks. Avoiding visual strain and allowing the brain time to recover is the primary recommendation before a formal medical evaluation guides a specific recovery plan.