Concussions can impact brain functions in many ways. High-level cognitive functions are the most likely to be disrupted because they involve many brain regions. When just one part of the chain of mental processing is affected, our ability to function can be critically impaired.
Of all the sensory information our brains process from moment to moment, vision dominates. In sports, for example, up to 90% of information coming in is processed by vision. This is why large areas of the brain are devoted to visual processing. The latest neuroscience research also reveals that vision is integrated with the ‘command centers’ of the brain, in the frontal lobe regions.
Here we’ll cover 5 keys ways visual performance can be disrupted by Mild Traumatic Brain Injury (mTBI).
1. Eye Tracking
When following an object in motion, such as a puck, soccer ball or an opponent, your eyes need to maintain focus while moving smoothly to maintain tracking. Concussions often affect the complex muscular system around the eyes. The result is jittery movements instead of precise pursuit movements, which leads to loss of focus. In turn, this creates visual noise making it much more difficult for the visual centers of the brain to interpret what is being seen.
For this reason, some vision assessments include eye-tracking tests, using a smooth pursuit task. If jittery eye movements are revealed, even if extremely subtle, it reveals a tell-tale sign that an individual is affected by mTBI, or a related cognitive impairment.
2. Peripheral Vision
Also known as side vision, peripheral vision is what is perceived around the outer edges of the visual field. Intuitively it seems simple to be aware of what’s going on around us, for example when driving a car or crossing a road. However, processing information across the peripheral visual field comes with a heavy mental load, particularly when the environment or perceiver is in motion.
In fact, it requires the activation of much larger neural networks compared to perception in the central field of vision. It’s also fundamental to balance, as the brain uses optic flow cues to understand it’s orientation in the world. This is why some advanced concussion assessments integrate balance tasks with stimulation of the peripheral vision, revealing effects of mTBIs that otherwise go unnoticed.
3. Visual Acuity
Visual acuity relates to clearly seeing, inspecting, identifying and understanding objects viewed at a near or far distance. It relies on accurate focus, requiring each eye to align precisely with an object being viewed. Dynamic visual acuity involves maintaining a clear focus on moving objects, including moving closer to, or further away from, the perceiver. This means both eyes must not only have accurate alignment but also maintain that accuracy simultaneously while changing viewing angles.
Similar to eye tracking issues, visual acuity places demands on fine grain ocular motor skills. Small impairments can significantly impair a person’s ability to focus on things in front of them. It’s a concern for athletes in post-concussion recovery phases. Particularly in team sports, fast changing, dynamic scenes place a constant strain on visual acuity. This stimulation can regress athletes back to being symptomatic after they had seemingly recovered.
4. Depth perception
Depth perception is the ability to see the world in three dimensions, coupled with the ability to judge the relative distances of objects – how far or near they are. There are many perceptual processes involved which utilize visual cues such as stereoscopy, perspective, texture, and tonal gradients. These cues are processed in separate regions of the visual centers of the brain, then pieced together by higher-order visual systems to generate a realistic sense of distance for everything in the environment.
Again, perceiving depth with absolute or relative motion will complexify demands on the brain. Depth perception is a critical factor in how we navigate the world safely, especially when driving.
If a concussion impacts any of the processes used to interpret depth, then the world around can become a very confusing place. As depth perception is a high-level visual function, interventions like NeuroTracker are used by concussion specialists to stimulate recovery of lost function and to bring athletes back to Return-to-Play status.
It may not sound like a visual skill, but attention and vision actually go hand in hand. The vast river of sensory data that flows into our brain far outweighs what we can actually process. To be efficient, attentional systems are used to detect what information is critical to our needs, and what is not. The visual centers of the brain then filter out what’s unnecessary, and prioritize mental resources onto what’s most important.
When this ability to selectively filter and process visual information is impaired by the effects of a concussion, even everyday activities like walking through a shopping center can become overwhelming. This type of sensory overload can quickly trigger mTBI symptoms such as dizziness, nausea and headaches.
Training the brain’s visual attentional systems through the concussion recovery process requires a Goldilocks approach. Visual stimulation that’s not too little, or too much, can be used to build back attention over time, step-by-step. NeuroTracker is used in this way by clinicians, who adapt the difficulty of the task to the precise needs of the individual, on a case by case basis.
As we’ve seen, vision is a complex system which can be affected in many ways by a concussion injury. Vision care professionals, such as neuro-optometrists, can play an extremely important role in rehabilitating visual functions to aid recovery. Furthermore, a great deal of neuroscience research is being devoted to discovering new ways to assess and regains visual functions impacted by mTBIs.