A concussion, classified as a Mild Traumatic Brain Injury (mTBI), is a temporary disruption of normal brain function. It is caused by a blow or jolt that makes the brain move rapidly within the skull, triggering neurophysiological changes that affect various systems, including those responsible for sight. While complete and permanent blindness is extremely rare, nearly 90% of patients report some form of visual disturbance following the injury. These symptoms usually relate to the brain’s ability to coordinate the eyes, rather than a problem with the eyes themselves.
Understanding Cortical and Ocular Mechanisms of Vision Loss
Severe visual impairment or blindness post-trauma stems from two distinct mechanisms: damage to the brain’s processing centers or direct injury to the eye’s physical structures. The most severe brain-related vision loss is Cortical Visual Impairment (CVI). CVI occurs when trauma affects the occipital lobe, the primary area of the brain dedicated to interpreting visual information. In CVI, the eyes are healthy, but the brain cannot process the signals, resulting in a loss of visual field or total sight.
The alternative mechanism involves direct ocular or orbital trauma, often associated with more severe head injuries than a typical concussion. This damage includes injury to the optic nerve, which transmits visual signals from the eye to the brain. The optic nerve can be compressed by a severe orbital fracture or swelling, leading to immediate and sometimes permanent vision loss in one eye. A detached retina is another form of structural damage, where impact causes the light-sensitive tissue to pull away from its blood supply, potentially resulting in blurred vision or complete blindness if not treated promptly.
Common Functional Visual Disturbances After Concussion
The majority of vision problems after a concussion are functional, arising from the brain’s temporary inability to coordinate the oculomotor system efficiently. One common issue is Convergence Insufficiency (CI), where the eyes struggle to turn inward to focus on near objects. This failure causes eye strain, headaches, and often leads to double vision (diplopia). Accommodative Dysfunction is also prevalent, manifesting as difficulty shifting focus smoothly between objects at different distances.
Another frequent complaint is photophobia, or increased sensitivity to light, affecting over half of concussed individuals. This symptom involves the disruption of pathways that regulate light processing, making normal lighting painful and debilitating. The brain’s control over eye movements is also routinely impaired, leading to problems with visual tracking. This results in difficulty following a moving object (smooth pursuits) or quickly shifting gaze between targets (saccades), which makes reading or navigating busy environments challenging.
These functional disturbances occur because the concussion temporarily impairs neural communication between the brainstem and the visual cortex. The resulting lack of coordination means the patient works harder to see clearly, leading to visual fatigue and difficulty sustaining concentration on visual tasks. These symptoms are typically temporary, but if they persist, specialized vision therapy focusing on retraining the eye-brain connection can be highly effective.
When Vision Symptoms Require Emergency Medical Attention
While many visual symptoms after a concussion are temporary, certain warning signs require immediate emergency medical attention. Any sudden, total loss of vision in one or both eyes should be treated as an emergency, as it may signal a catastrophic event like a detached retina or acute optic nerve compression. Pupils that are unequal in size or react sluggishly to light may indicate increased pressure within the skull, which demands urgent assessment.
Physical changes around the eye, such as noticeable bulging or the presence of clear fluid or blood draining from the ears or nose, must prompt an immediate hospital visit. This drainage may suggest a skull fracture that has compromised the integrity of the brain cavity. If double vision is persistent and rapidly worsening, or if it is accompanied by a severe, unrelenting headache, these symptoms could signal a developing hematoma or other intracranial bleeding.