A concussion is defined as a mild traumatic brain injury (mTBI) that causes a temporary disturbance in how the brain functions. This injury occurs following a bump, blow, or jolt to the head, or a forceful hit to the body that causes the head and brain to move rapidly. The sudden movement can cause the brain to twist or bounce inside the skull, leading to chemical changes and stretching of nerve cells. A concussion is a serious medical event that requires professional attention.
The Neurological Basis for Visual Changes
The visual problems accompanying a concussion arise because a large portion of the brain is dedicated to processing visual information and controlling eye movement. Approximately half of the brain’s circuitry is involved in the visual system, making it highly susceptible to trauma. When the brain moves violently within the skull, it disrupts the neural pathways responsible for sight and eye coordination.
The primary visual processing center is the occipital lobe, located at the back of the brain, which interprets signals from the eyes. Impairment to this area can lead to difficulties with visual perception, spatial awareness, and depth perception. The mechanical control of the eyes is handled by three specific cranial nerves: the oculomotor (III), trochlear (IV), and abducens (VI) nerves. Their disruption can lead to a breakdown in the eyes’ ability to work together, as they coordinate eye movement and pupil response.
Observable Physical Signs in the Eyes
A bystander or caregiver can often observe several objective signs in the eyes of a person who has sustained a concussion. These physical manifestations reflect the neurological disruption caused by the injury.
Pupil Irregularities
One major red flag involves pupil irregularities, which are controlled by the oculomotor nerve. The pupils may become unequal in size, a condition called anisocoria, or they may be noticeably dilated. The reaction to light may also be sluggish or delayed. When a light is shined into the eye, the pupil should constrict quickly, but a slow or absent response indicates an issue with the nerve pathway.
Eye Tracking and Alignment Issues
Eye tracking and alignment issues are common physical signs of oculomotor dysfunction. The eyes may fail to move together smoothly, resulting in a disconjugate gaze. One eye may also appear misaligned, which is known as strabismus. When asked to follow an object, the eyes might struggle to track the movement in a coordinated manner, often moving in a jerky fashion.
Nystagmus
Another visible sign is nystagmus, which is the involuntary, repetitive, and uncontrolled movement of the eyes. This rapid, shaky motion often occurs when the person tries to focus or look to the side. Nystagmus is a sign of damage to systems that control eye stability, such as the vestibular system. These signs are often accompanied by the patient reporting symptoms of blurred or unstable vision.
Subjective Visual Symptoms Reported by the Patient
While some visual signs are observable, many common post-concussion visual issues are subjective experiences reported by the injured person. These symptoms stem from the same underlying neurological disruption but are felt rather than seen.
Photophobia
Extreme sensitivity to light, known as photophobia, is a frequently reported visual symptom after a concussion. This sensitivity can make environments with bright sunlight or fluorescent lighting painful. It results from the brain’s inability to properly modulate sensory input. Photophobia is considered the second most common symptom of a concussion overall.
Blurred Vision and Diplopia
Many patients report blurred vision or diplopia, which is the perception of double images. Double vision occurs when the eyes cannot align precisely to focus on a single point, causing two different images to be sent to the brain. Blurred vision may also be related to accommodative insufficiency. This is the eye’s reduced ability to focus on near objects, leading to difficulty with reading and screen time.
Visual Field Changes
Patients may also describe visual field changes, such as seeing spots, floaters, or flashing lights, a phenomenon known as photopsia. These visual disturbances can be transient and result from the spontaneous firing of neurons in the occipital lobe upon impact. Some individuals may experience an overall feeling of “tunnel vision,” where their peripheral vision feels constricted, or they might struggle with depth perception.
Seeking Immediate Medical Attention
Any suspicion of a concussion, especially one involving visual symptoms, warrants immediate professional medical evaluation. Certain visual signs, such as pupils of unequal size or an inability to track objects, can indicate a more severe injury, like bleeding in the brain, and require emergency care.
A healthcare provider trained in concussion management will perform a neurological assessment that often includes tests of the visual and oculomotor systems. The Vestibular Ocular Motor Screening (VOMS) is a common clinical tool used to challenge the visual system through various eye movements. If these specific visual tasks provoke or worsen symptoms like headache, nausea, or dizziness, it provides objective evidence of brain dysfunction.
Even if visual symptoms seem mild, like slight light sensitivity or minor blurring, they should be reported to a medical professional. These symptoms are frequently used to monitor the recovery process and guide decisions regarding a safe return to daily activities. Ignoring visual complaints can delay recovery and potentially lead to chronic issues with headaches or balance.