Balance plays a critical role in mobility and vision plays a critical role in balance. This session will focus on the impact of vision loss on balance and gait, discuss issues for professionals, and suggest strategies for instruction and intervention with students who have balance problems.

The Balancing Act:
What Role Does Vision Play?
Presented by Denise Gobert, PT, PhD
Texas State University, San Marcos, TX dgobert@txstate.edu
Objectives:
 How sensory systems are used for balance and coordination
 Assessment criteria for gait deficits associated with visual impairments
 Helpful points to aid prescription of devices used to improve gait
Sensory Feedback Supporting Gait & Posture
QuickTime™ and a
decompressor are needed to see thi s pi ctur e.
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Balance Using the Senses
Gobert -2008
NeuroCom International, Inc. Body Movement
Modified from Neurological Rehabilitation 5thEd., Umpherd, 2007
Determination of Body
Position
Choice of
Movement
Compare, Select &
Combine Senses
Vision Vestibular
System
Environmental
Interaction
Somatosensation
Generation of
Body Movement
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Egocentric vs. Exocentric
 Egocentric –Internal body reference system (internal body map)
 Exocentric –External body reference system (External environmental map)
Egocentric Information
 4 –6 y/o motor reflexes more chaotic than 3y/o
 < 7 y/o unable to correctly use conflicting sensory information for balance
 Adult-like gait developed at 7 yrs old
Ankle Strategy Hip Strategy
Figure 3: Ankel and hip strategies in stance posture
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Vestibular Input
 Egocentric Information
 Helps to distinguish between exocentric & egocentric motion
 Keeps Gaze platform stable
 Reference to verticality
Vestibular Anatomy greater saccular nerve
QuickTime™ and a
decompressor are needed to see this picture.
endolymphatic sac
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Static Vestibular Angles
 Linear Acceleration
 Uticle is in horizontal plane
 Saccule is in vertical plan
Quic kTime™ and a
dec ompres sor are needed to see t his pic ture.
Linear Acceleration
Utricle is in horizontal plane
Saccule is in vertical l plane
Angular acceleration of head
Semicircular canals are orthogonal to each other
Lateral canal inclined to 30°
Superior/posterior canals 45° off of sagittal plane
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Spatial Hearing
Interaural Difference
= 0.63 ms Delay Exocentric information
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Visual Input
Exocentric information
Peripheral Optic Flow = postural control
The “2-sec” action window
Decreased visual info = decreased hip strategies for balance
Ankle Strategy Hip Strategy
Figure 3: Ankel and hip strategies in stance posture
Visual Input
 Helps determine gait speed
◦ Double optical flow = increased perception of stride length
◦ Tilt visual field = tilt of head/trunk
Vision Supports Proactive Strategies
Avoidance strategies
◦ Change in foot placement
◦ Increase ground clearance to avoid obstacle
◦ Change direction of gait (obstacle can’t be cleared
◦ Stopping
Accommodation
◦ Reduce step length on slippery surfaces
◦ Shift propulsive power from ankle to hip/knee
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Visual Deficits Lead to Postural Deficits
 Head Tilt with control during ambulation
 WBOS –slowed/ shuffling pattern
 Neglect of specific areas of body/ space
 Incorrect posturing to negotiate obstacles
Assessment
….How many resources are available for successful gait? ….
Basic Assessment Areas
 Residual Visual Function
 Static vs. Dynamic Posture
 Gait & body coordination skills and other gross motor techniques
 Cognitive abilities
What do the eyes see?
(Pictures of two boys with balls and cross section of the brain including the eyeball and optic nerve.)
Basics of Visual Function
 Normal Vision = 20/20
 Vision Services needed = 20/70
 For school aged children
 Day-time driving only 20/40
 Legally Blind = 20/400
 Residual sight may still be present
(Pictures of various eye charts)
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“Counting Fingers” Visual Scale
Vision worse than 20/400 as Count Fingers (CF at a certain number of feet)
Hand Motion (HM at a certain number of feet),
Light Perception (LP) or No Light Perception (NLP)
The conversion of Snelllen Acuity to Count Fingers Acuity is as follows:
20/800 (Count Fingers at ten feet)
20/1000
20/1143
20/1333
20/1600
20/2000
20/2666
20/4000
20/8000
Functional Spatial Orientation
Directionally specific neuronal activity associated with movements.
(Georgopoulous 1993, 1994a, 1994b)
Spatial Concepts
 Relationship to environment
 Distance, size and directional concepts
 Sensory Maps (Smell, Hearing, Tactile)
Muscular Coordination
Bimanual Motor Coordination
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Movement Skills
 Searching Skills
 Protective Skills
 Bruininks-Oseretsky Test of Motor Proficiency (BOTMP)
 Bouchard et al. The Motor Development of Sighted & Children with Mod
Low Vision Aged 8-13”, J of Vision Impairment & Blind, Vol 94(9) 2000.
Sensory Use for Functional Gait
Cognitive Function?
 Can the client learn?
1.
New motor skills?
2.
New feedback systems?
 Southern California Figure-Ground Visual Perception Test
 Sensory Integration & Praxis Test (Ayres)
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Assistive Technology
…How might we compliment available resources for successful gait? …
Needs assessment of gait assistance
Exocentric vs. Egocentric Feedback?
 Residual vision - aid or hindrance?
Postural support for balance?
 Head/trunk positioning
Spatial Orientation for balance?
 Postural Verticality?
Avoidance / Accommodation Strategies ?
 Anticipatory postural control?
Low Tech Assistance
Cane
Sighted Guide
Adaptive Mobility Device
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Cane Mobility Strategies
 Typical cane techniques: arc, rhythm step, shore-lining, touch and slide, diagonal, stationary landmarks or other points of reference; negotiation of curbs and uneven terrains.
 What is the demand on the sensory system?
The Cane: Pros and Cons
 6”-16” below top of head “sternal Height”
 Extension of egocentric space (3’-8’) (Serina et al. Psych.Sci 2007, Vol.
18 (7): pp.612-618)
 Object / Surface preview
 Foot placement preview
 Disadvantage: No upper body protection, “touch technique” = inadequate foot placement preview
High Tech Assistance
 Artificial Exocentric Feedback:
Sonar Devices
Auditory Feedback Devices
 Extends Feedback range 12’-25’
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Artificial Visual Support of Gait
Figure 5: Obstacle detection. (a) The original image . (b) Result from
Ground Plane Obstacle Detection. (c) Result from RANSAC Dynamic Ground
Plane Recalibration.
High Tech Assistance
Sonic Pathfinder
Wheelchair Pathfinder
Laser Cane
Auditory Feedback for Gait
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Let’s Try Some Tests!
 Quick Vision Testing – Residual Vision
V-MAX Demo
 Fukuka Stepping Test – Balance
Handout
 Cognition Testing – Walkie Talkie Test
Lundin-Olsson, L., Nyberg, L., & Gustafson, Y. (1997) “Stops walking when talking” as a predictor of falls in elderly people. Lancet 349, 617.
Take Home Points
Access to Egocentric / Exocentric Feedback?
Balance & Coordination?
Cognitive Skills?
All dictate safe prescription of Mobility Assistance for the Visually
Imapired
Questions & Answers
Helpful Resources
 Association for Education & Rehabilitation of the Blind & Visually
Impaired (AER) –Division 9 – Orientation & Mobility: (703) 823 –9690
 Lighthouse International: www.lighthouse.org
 American Foundation for the Blind: www.afb.org
 Simons & Maida, (1992), Reaching, Crawling, Walking .. Orientation &
Mobility for Preschool Children : http//www.blindctr.org/bcc/pubs.htm
 Umpherd D.,(2007), Neurological Rehabilitation 5th Ed, MOSBY.
 Ayres, A. Jean.(1994), Sensory Integration and the Child. Los Angeles:
Western Psychological Services.
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