CVI: Visual Guidance of Lower Limbs

Written by: Rachel Bennett

At Perkins, we are a gathering place of ideas. The CVI visual behaviors synthesize current research and build on the work of leading theorists in the field. CVI is a lifelong disability and we want to ensure that all individuals with CVI are fully understood. The CVI visual behaviors are an ongoing need, they can change and they can improve for some, but the need never goes away. No one area is separated from the other—the CVI visual behaviors are highly connected and all can impact the individual with CVI at any time.

What is Visual Guidance of Lower Limbs?

Visual Guidance of the Lower Limbs refers to visual motor skills in relation to foot-eye coordination. Some people with CVI may demonstrate:

reduced visual attention to their lower limbs
difficulty placing their feet correctly on targets
navigation challenges, resulting in tripping or frequent falls
overstepping or under stepping when approaching changes in depth
challenges walking over uneven ground

Visual guidance of the lower limbs may be further impacted by: the floor surface, visual crowding of the environment, size and contrast of the items on the floor, motion in the environment, changes in light, and simultaneous auditory input.

Navigating steps, sidewalks, patterned surfaces, and patterned carpets is almost impossible for me if I don’t use a cane. Patterned carpets are a nightmare.
Dagbjört, adult with CVI, from Why music is my vision: Dagbjört talks about living with CVI as an adult

What are some compensatory strategies related to Visual Guidance of Upper Limbs?

Many with CVI build strategies to compensate for difficulty with visual motor skills. Some of these strategies include:

Using mobility supports, such as a white cane
Using tactile skills and cues: toe-tapping the surface before advancing; sliding feet on stairs; heavily relying on holding a railing when navigating changes in depth
Slowing down, pausing, or bringing their body lower to the ground at changes in depth, thresholds, floor changes
Step counting
Scheduling travel for when there is less commotion and noise
Relying on memory to travel within familiar or reliable environments
Relying on a trusted person when navigating
Using changes in color and presence of shadows to note a change in depth or change in surface
Avoiding patterned and cluttered surfaces all together

I’m learning to use a white cane now. I can’t see steps at all. I have poor depth perception.
Albie, from Albie’s CVI Perspective

What are some look fors/questions when observing your child with CVI?

When it comes to observing visual motor skills, take into consideration how these skills are impacted by color, motion, field, clutter, light, recognition, competing sensory information, familiarity of object or environment, in addition to fatigue and time of day.

Does your child with CVI navigate subtle changes in depth (i.e., single curb) with ease or difficulty? Do they ascend stairs with ease or difficulty? Do they descend stairs with ease or difficulty? Does familiarity with the environment impact these abilities?
Do they consistently over- or under-step when navigating changes in depth?
Does color high-lighting impact the individual’s ability to efficiently navigate changes in depth?
Is your child’s ability to navigate changes in depth decreased or not impacted by visually busy environments?
Do they heavily rely on the railing when navigating changes in depth?
Do they rely on assistive devices when navigating changes in depth (i.e., white cane)?
To what extent do they use tactile supports when navigating changes in depth? For example, sliding foot on the stair, over-relying the hand railing, toe-tapping the ground to locate and judge changes?
Do they slow down, pause, or bring their body lower to the ground at changes in depth, thresholds, or floor changes?

CVI gives me a better understanding of my son’s interaction with the world. We were visiting a lake yesterday and he went out on a narrow pier. He got very fearful and told me to be careful as it was very unstable and wiggly. When I walked out on it I found it to be rock solid and no movement at all but I noticed the water to be very choppy. My son got off the pier and proceeded to throw rocks into the water for 20 minutes… to help regulate after this scary moment on the dock.
Delia, CVI parent

What are some examples of adaptations and accommodations?

All accommodations must be based on assessment. The following are meant to inspire and provide a general idea. Accommodations and instructional approaches must be student-specific. Access is individual.

A team must consider all the other CVI visual behaviors when supporting visual motor tasks, along with the student’s whole-child needs. What compensatory skills can we leverage to make sure navigating the multiple environments in both the school and community are fully accessible? Here are some adaptations and accommodations that can support safe navigation for some with CVI.

Allow for navigation when hallways and spaces are quiet and less busy. Getting around the school when the hallways are filled with people and noise can be extremely overwhelming and fatiguing for a student with CVI, and it can keep them from being able to engage in safe and independent navigation. Allowing them to go to the lunch room before it’s busy or changing their classroom before everyone else is in the hallway can make for a more accessible and sustainable school day.
Use bright, bold colors to highlight railings, top and bottom of stairs, and ramps to support visual attention and recognition, and alert the person with CVI that these elements are in the environment. Use visual and tactile markers to note approaching changes in depth.
Use of a white cane to support safe navigation in a wide variety of environments. A white cane, and other mobility devices, can help navigate changes in depth, obstacles, uneven surfaces, busy/patterned surfaces, change in surfaces, and when in new, busy environments.
Provide verbal cues and support in new environments. Talk through changes in depth and surface. Practice compensatory strategies to navigate and learn this new space.
Use of step counting to support navigation of stairs, hallways, and out in the community.

Find more examples from a guide to common CVI IEP accommodations in the CVI Now IEP Guide.

My son took to his white cane really quickly, and he’s often hesitant to try new things. Over the course of the past three years, I’ve seen his confidence and independence increase when he’s out in the community. His white cane and learning blindness skills allows him to build agency.
CVI parent

Following the science

Connecting current research of the brain, our visual system, and CVI to better understand the CVI visual behaviors.

Optic Ataxia is impaired coordination and accuracy of visually guided movements of limbs and body not related to motor complexities. Optic Ataxia results in difficulty completing visually guided tasks. This impacts the ability to judge distance, depth, and weight, which is needed for motor action. Damage or interruption to the posterior parietal cortex is connected to optic ataxia.

Depth perception (stereopsis) is the ability to judge the distance between objects and see the world in 3D. Research shows that depth perception is absent or altered in many with CVI. The early visual pathway, primary cortex, and ventral visual pathway all play a role in the ability to perceive depth. Ocular impairments such as strabismus and nystagmus can reduce depth perception, along with damage or interruption of the ventral pathway. Our visual system uses many cues and processes so we can use depth perception to make sense of the visual world, all of which is done without conscious thought. These are complex processes. Here are some highly simplified examples:

Linear Perspective – parallel lines converge as they travel away from us
Relative Size – things closer to us appear bigger
Texture Gradient – seeing textures more clearly when close to us
Interposition – if something blocks the view of another object, it’s closer
Shading – the way shadows fall tells us how close things are to us
Motion Parallax – things appear to move at different speeds based on distance
Optic Flow – the way things move on our retina tells the distance, also incorporating relative size
Disparity – two versions from different angles combined into one. The difference indicates the depth, and the angles change with distance.
Vergence eye movements – two eyes move differently based on if something is close (convergence, move inward) or far away (divergence, move outward) in order to maintain binocular vision

Visual-spatial mapping: The dorsal visual stream (occipital to parietal to frontal lobes) plays a major role in creating an unconscious 3D map of the world around us. Why is this important for visual guidance of limbs? When this 3D mental map doesn’t match the reality of the surrounding environment, the result is Optic Ataxia. According to Dr. Gordon Dutton in CVI Scotland’s lesson on Optic Ataxia: “This 3D map matches where things are in the real world, in terms of how far away they are, and gives every visual detail the properties of depth and distance in your mind. To move through the real world without bumping into people and things and to reach for things with accuracy, these two worlds (world 1 is the reality of the surroundings, and world 2 is the non-conscious mental copy of them) need to match.”

Here are three examples of how some with CVI use their compensatory skills to go down the stairs: slide their heel along stairs, rely on the railing, and toe-tap to make sure there are no more stairs.

References

Atkinson, J. (2017). Visual Brain Development: A review of ‘‘Dorsal Stream Vulnerability’’—motion, mathematics, amblyopia, actions, and attention. The David Teller Award Lecture, 2016. Journal of Vision, 17(3): 26, 1-24.

Atkinson, J., & Braddick, O. (2011). From genes to brain development to phenotypic behavior: “dorsal-stream vulnerability” in relation to spatial cognition, attention, and planning of actions in Williams syndrome (WS) and other developmental disorders. Progress in Brain Research, 189, 261–283.

Chokron, S. & Dutton, G. N. (2016). Impact of cerebral visual impairments on motor skills: Implications for developmental coordination disorders. Frontiers in Psychology 7(1471), 1-15.

Chokron, S., Klara, K., & Gordon D. (2021). Cortical Visual Impairments and Learning Disabilities. Frontiers in Human Neuroscience 15, 573.

Fazzi E, Signorini SG, Bova SM, La Piana R, Ondei P, Bertone C, Misefari W, Bianchi PE. (2007). Spectrum of visual disorders in children with cerebral visual impairment. J Child Neurol. 22:294-301.

Goodale, M. A. (2013). Separate visual systems for perception and action: a framework for understanding cortical visual impairment. Developmental Medicine and Child Neurology, 55(4), 9-12.

Greulich, R. S., Adam, R., Everling, S., and Scherberger, H. (2020). Shared functional connectivity between the dorso-medial and dorso-ventral streams in macaques. Sci. Rep. 10, 1–17.

Kelly, J., Phillips, J., Saneto, R., Khalatbari, H., Poliakov, A., Tarczy-Hornoch, K., & Weiss, A. (2021). Cerebral visual impairment characterized by abnormal visual orienting behavior with preserved visual cortex activation. Investigative Ophthalmology and Visual Science, 62(6), 1-11.

Lueck, A. H., & Dutton, G. N. (2015). Vision and the Brain: Understanding Cerebral Visual Impairment in Children (pp. 497-536). New York, New York: American Foundation for the Blind Press.

Philip, S.S. and Dutton, G.N. (2014), Cerebral visual impairment in children: a review. Clin Exp Optom, 97: 196-208.

Roman-Lantzy, C. (2018). Cortical Visual Impairment: An Approach to Assessment and Intervention. 2nd ed., New York, NY: AFB Press.

Van Polanen, V., and Davare, M. (2015). Interactions between dorsal and ventral streams for controlling skilled grasp. Neuropsychologia 79, 186–191.

Whitwell,R., Sperandio, I., Buckingham, G., Chouinard, P., Goodale, M. (2020). Grip Constancy but not Perceptual Size Constancy Survives Lesions of Early Visual Cortex. Current Biology. Vol 30, Issue 18. https://www.sciencedirect.com/science/article/pii/S0960982220310186