by: Aubrey Breithaupt, OD
Have you ever tried balancing on one foot or standing heel-to-toe with your eyes closed? It is not as easy as one would think to maintain proper body positioning and balance without the use of our vision. Attempting this, you might start to sway, wobble, or tip over and eventually have to catch yourself by putting your other foot down or stepping to the side. What is it about our vision that helps keep us balanced and centered?
Most of us are aware that the light that enters our eyes is sent to our brain to be interpreted as what we call “vision,” but did you know that some of this information is NOT used for vision as we think of it? Most of the visual information captured by our eyes is sent to the posterior (back) part of our brain to be processed and interpreted as what we “see.” This is called the “focal” visual system, and it provides us with conscious, detailed information about WHAT we are looking at – what colors we see, what objects we are looking at, how large the objects are, and all of the other detailed information that allows us to analyze and discriminate what we are viewing. That said, however, 20% of the visual information we receive through our eyes is actually sent to a different part of the brain that is not used to analyze WHAT we see, but to interpret WHERE we are in space in relation to other people and objects. This important part of our vision is called the “ambient” visual system, and it is responsible for helping us understand the space around us and how to move about efficiently within our environment.
Before we can interact effectively with our visual world, we first need to have a sense of “center” for our bodies to understand the space around us and to control our balance and posture. This sense of center is called our “midline,” and if our ambient vision and other sensory systems are integrated and functioning properly, our midline is centered between both the right and left halves of our body and the front and back halves of our body. The ambient visual system provides about 1/3 of the sensory information that contributes to our midline, but the other 2/3 of this information comes from both the vestibular system (interprets movement and acceleration) and the proprioceptive system (provides sense of limb/body positioning and movement). These three sensory systems must be integrated properly to provide accurate information about our midline and the space around us, otherwise we can experience dizziness, motion sickness, poor balance, poor depth perception, and poor spatial awareness.
Several of the symptoms listed above are common complaints of individuals who have suffered an acquired brain injury (ABI) such as a concussion or stroke, which are frequently attributed to poor organization and integration of the ambient vision, vestibular, and proprioceptive systems. Other individuals that may experience these types of symptoms and poor integration of their sensory systems are individuals with neurological conditions such as general developmental delays, autism, Down Syndrome, cerebral palsy, and Parkinson’s disease to name a few. Often times these individuals will also experience difficulty understanding and interpreting movement as well because the same three sensory systems contribute to our ability to process motion. Other common deficits include poor eye movements/tracking, difficulty teaming the eyes together, and inaccurate focusing skills. Our eyes must first know WHERE to look (ambient visual system) before we can expect our visual system to understand WHAT we are looking at (focal visual system) and to move and adjust efficiently to the visual task at hand.
Though the effects and symptoms related to dysfunction of our ambient vision and related sensory systems can be frustrating for those who experience these difficulties, the good news is that vision therapy can help! Most individuals who pursue treatment through vision therapy have very successful outcomes with reduction of symptoms and improved quality of life. Therapy can also help improve other foundational skills of our visual system, such as how our eyes are teaming together, tracking, and focusing. Improving these functions to their fullest potential can help maximize performance for activities such as reading, working, and learning to improve productivity and efficiency throughout our daily lives.
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