April 19, 2017
The Eyes Have It: Dynamic Systems At Work
For the last 2 posts, I have been discussing some of the details regarding functional vision – what it is, how it develops and its important contribution to movement. If you missed these, you can read them here and here.
It can be challenging as a PT to decipher the information regarding the impact of functional vision, as much of it is discussed in the context of reading skills. However, if we consider that visual-vestibular sensory input is the primary information for postural control until we are 3 years old1, its importance to movement becomes crystal clear. (Following on from that, from 4-6 years we begin to use this visual-vestibular information in combination with somatosensory input for postural control, at 8 years we begin to be able to utilize sensory selection and usually by age 12, we can solve conditions of sensory conflict1-3).
My last post looked at some of the basic eye movements that contribute to visual efficiency. It is important that PTs be able to complete a functional vision screen to assess how well the eyes are working together. Remember that if they are not working well together, then depth perception will be disrupted and this in turn has a huge impact on movement. My functional vision screen includes the quality of these skills: vergence, saccades, smooth pursuits, fixation and peripheral vision (you can see these demonstrated in the videos in my last post). In each of these, we are looking for whether the child can complete the skill, how smoothly the eyes move together or if one eye is slower than the other, if the eyes lose focus on the object and if that point is consistent (always on the left or when crossing midline or 3″ from the nose etc), if the eyes jump ahead of the object and lastly the size of the peripheral visual field, if the fields are equal left and right and whether the child can utilize peripheral and central vision.
I recommend testing these skills in the child’s natural posture in sitting and in standing. (Testing only in sitting may be fine if you are only concerned with function in sitting, but as PTs we are going to be interested in how a child uses their eyes in standing and eventually walking/playing as well so we need to screen in at least one position further up against gravity as well.) Then re-test in sitting using the optimal alignment that supports central stability and note any differences in functional visual skills in these two postures. (If you want to read more about this, you can refer to blogs here and here or you can take my online course Dynamic Core for Kids to learn a total approach to assessment and treatment of central stability for children with motor and sensory challenges). Sometimes it will take a few sessions for the child to develop the necessary central stability in sitting, so you can wait and re-screen at that time (this is also why I don’t re-screen immediately in standing as it takes longer for the child to develop stability in this position).
To experience the impact of alignment on visual function, you can try this experiment. Sit and slump down in your chair (like the man in the picture) , then perform the simple vergence activity several times. Do you find the activity difficult to complete or tiring for your eyes? Now adjust your alignment; place your pelvis in just a suggestion of anterior tilt and stack your rib cage overtop of your pelvis. Perform the vergence activity again. Some of you will notice that it is easier to perform the activity in the adjusted posture. This is the impact of alignment, stability and neuromotor recruitment!
Lastly, if the child can participate, play a bean bag toss game as part of the screen for eye-hand-body or visual motor coordination. Sitting across from the child, instruct them to follow the beanbag with their eyes. Toss a bean bag from your right hand, to child’s left hand, child passes bean bag to right hand and tosses to your left hand. After several repetitions, we reverse the direction (this is known as a one-bag rectangle in Bal-A-Vis-X training). We are watching for how the child positions themselves for the task, any changes in position or alignment during the task, how they visually track the bean bag, can they cross midline with the bean bag and with their eyes. All of these speak to the quality of their eye-hand-body coordination.
Once we address central stability and have gained some mastery of these activities in sitting, it is time to progress to standing and then to balance activities. We remember that quality anti-gravity function is crucial for quality functional vision and that it is particularly challenging as the kids come further up against gravity. We often have to address increased recruitment and strength in more difficult anti-gravity flexion activities and then carefully layer this with gross motor function and visual function.
During the initial activities, we are watching for the impact of central stability on functional vision. Most often a functional vision assessment with a developmental optometrist is the best option for care. You can see from the picture below that the first step in vision therapy is gross motor control (balance & gait). As therapists we have the most in-depth, up-to-date understanding of core stability and postural control so teamwork is essential.
Finally, treatment progresses to higher level activities that can combine balance, rhythm, vision and cognition. One of my favourites is the Infinity Walk. Here is a simple demonstration/explanation of the activity but the variations are endless!
So that’s it, we’ve come to the end of this 3-part series on functional vision. I hope it has helped to introduce you to some of the vision basics, it’s impact on movement and a few of the foundational concepts of assessment and treatment. Ultimately we understand that visual, vestibular and motor networks really are dynamic systems, interconnected in so many ways and we impact on multiple levels during every part of our intervention.
1. Foudriat BA, Di Fabio RP, Anderson JH. Sensory organization of balance responses in children 3-4 years of age: a normative study with diagnostic implications. Int J Pediatr Otorhinolaryngol. 1993; 27(3): 255-71.
2. Rinaldi NM, Polastri PF, Barela JA. Age-related changes in postural control sensory reweighing. Neurosci Lett. 2009; 467(3): 225-9.
3. Fujiwara K, Kiyota T, Mammadova A, Yaguchi C. Age-related changes and sex differences in postural control adaptability in children during periodic floor oscillation with eyes closed. J Physiol Anthropol. 2011; 30(5): 197-94