Changes in Occupational Performance Resulting from Visual Field Deficit

1
Changes in Occupational Performance Resulting
from Visual Field Deficit
2
Behavioral Changes

• Four behavioral changes occur following onset of
  VFD
• They explain the limitations observed in
  occupational performance

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Behavioral Change 1

• Adoption of a narrow, restricted search pattern
  confined to midline and sound side
• Person narrows their scope of scanning
• Seems paradoxical in that one would expect the
  patient to widen their scanning in an effort to
  see around the blind spot
• Occurs because of perceptual completion

4
Perceptual Completion

• Normal perceptual mechanism used to increase
  speed in visual processing
• CNS samples visual array internally completing
  scene based on expectation of what will be found
  in array

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Even with a visual field deficit as large as a
hemianopsia, the CNS will perceptually complete
the missing field
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Because of Perceptual Completion

• Initially person is unaware of VFD
• Gradually discovers loss through interaction with
  environment
• Experiences collisions etc
• But often misinterprets mistakes as being due to
  altered depth perception
• Learns to distrust deficit side and focuses
  attention on sound field
• Reduces visual search to deficit side
• Person restricts scanning to midline and sound
  side

7
Restriction in Scanning

• Will prevent person from noticing obstacles in
  environment contributing to
• Collisions
• Disorientation
• Will prevent person from noticing objects in
  environment contributing to
• Difficulty locating items needed for ADLs
• Appearance of neglect
• (but person does not have neglect)

8
Behavioral Change 2

• Even when aware of deficit, person scans very
  slowly towards deficit side
• Cause because of perceptual completion, person
  doesnt have the benefit of a distinct boundary
  between the seeing and the blind field
• Doesnt know when hes in the blind field or how
  far to go to locate a target

9

• You can imagine the dilemma of the hemianopic
  person by picturing yourself at the front of a
  long tunnel. The tunnel is pitch black inside.
  You are instructed to run down to the end of the
  tunnel as fast as you can. Not to worry-youll
  know when youve reached the end of the tunnel
  because there is a wall down there and youll run
  into it.
• WILL YOU RUN FAST OR SLOW DOWN THE TUNNEL WHEN
  YOU CANT SEE WHERE YOU ARE GOING??

10
Slowed Search

• Prevents person from completing activities in a
  timely manner
• Very frustrating
• In dynamic tasks, like driving, may prevent
  person from safely completing the task

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Behavioral Change 3

• Missing and/or mis-identifying visual detail on
  the blind side
• Occurs if foveal area in macula is involved
  creating macular scotoma
• Person will miss visual information falling into
  the scotoma

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Missing/Mis-identification

• Can significantly impair reading performance
• Omits or transforms words
• Can cause incomplete performance of tasks
• Only eats part of the food on plate
• Can cause inaccurate task completion
• Dials the wrong telephone number because he
  misread the numbers on the pad

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Behavioral Change 4

• Reduced visual monitoring of the hand during
  completion of activities
• Only occurs if VFD is on the same side as the
  dominant hand
• And the VFD affects the foveal/macular area

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Reduced Visual Monitoring

• Can reduce
• Legibility of handwriting
• Accuracy in pouring
• Completion of tasks requiring fine dexterity
• Sewing/threading a needle

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Behavioral changes create deficits in orientation
and mobility and reading and writing. These
deficits, in turn, cause limitations in a variety
of daily living activities.
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Orientation and MobilityAmbulation

• Shortened and uncertain stride
• Due to inability to monitor support surface
• Uncertainty approaching, negotiating changes in
  support surfaces
• Curb etc.
• Frequent collisions with unexpected objects
• Adoption of shoe/floor gazing
• Using of trailing and other tactual strategies

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Orientation and MobilityPostural Adaptation

• Often complain of decreased balance
• Rondot, Odier, Valade (1992)
• Persons with hemianopsia display greater
  displacement of body weight towards VFD side
• 4x times greater displacement than norms
• Still present 7 years post
• Balance instability may be due to reduction in
  peripheral visual input on blind side
• Shift of gravity center towards VFD may
  contribute to collisions with objects on VFD side

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Orientation and MobilityOrientation to Space

• Often see significant deficits due to
• Erroneous perception of field provided by
  perceptual completion
• Inability to scan fast enough over a dynamic
  scene to comprehend the scene as a whole
• CNS doesnt get enough visual input to build
  working topographical memory

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Orientation and MobilityOrientation to Space

• Disorientation
• Literally get lost in space as CNS doesnt get
  pertinent visual cues
• Double whammy if occipital lesion occurs as
  person may also lose ability to make saccades
  towards acoustic targets
• Affects safety in dynamic environments
• Adapt by following others and avoidng dynamic
  environments

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Limitations in Reading

• Occur if fovea and macula are involved
• Affected by both left and right hemianopsia
• Miss or misread words
• Lose place on line, skip lines
• Experience reduced speed and accuracy
• Caused by alteration of perceptual (visual) span

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Perceptual (visual) Span

• Field of useful vision during eye fixation
• Can be thought of as a window
• Relies on foveal and parafoveal field
• Foveal acute detailed vision to see letters
• Parafoveal less acute, provides gross feature
  detection
• and perception of length and shape of words
• Has spatial and temporal dimensions
• Spatial
• Approximately 8 degrees or 10-15 characters wide
• Asymmetrical, extending farther to right than
  left
• Temporal
• fixation time of 200-250 ms within the perceptual
  span is required for skilled reader to recognize
  a word

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Perceptual Span continued

• Person fixates in the middle of a word
• Shifts gaze fixation from middle of one word to
  the middle of the next word
• Skips over small words, spaces
• Gaze shift is driven by parafoveal vision which
  detects presence of letters to right side
• Foveal and parafoveal input is used by reader to
  maintain continuous acquisition of text
  information reducing recognition time

23
Perceptual Span in Reading


President Ge
Bush went to
George Bus
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Reading Comprehension

• For comprehension to occur
• Word recognition must be completed within a
  specific time period
• Words must be read with fluency (accuracy and
  rhythm)
• The fewer the fixations and the shorter their
  duration, the faster the reading speed

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Hemianopsia

• Shortens the perceptual span
• Causes misidentification or omission of words
• Snow is read as now
• Hanger is read as hang
• Person is forced to commit a regression (re-read
  the word)
• Or in the case of RVFD, forced to spell the word
  for it to make sense
• Both types of errors reduce reading speed and
  accuracy

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• Significance of reading deficit is determined by
  the degree of field sparring
• The closer the scotoma border is to the fovea,
  the more impaired the reading
• Most reading errors are made by persons with 1-2
  degrees of field sparring
• Rt VFD 67
• Lt VFD 84
• Reading speed is slowed as person is unable to
  use parafoveal vision to assist in guiding
  reading saccades

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Patient with left homonymous hemianopsia imaged
with a scanning laser ophthalmoscope
Reading performance is influenced by how closely
the border of the scotoma (ds) comes to foveal
fixation Example 1 scotoma border is less that
2 deg from fixation and and influences
reading more than Example 2 where border is
farther away
Fixation
Example 1
Fixation
Example 2
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Reading DeficitsRight vs.Left VFDZihl J, Eye
Movement Patterns in Hemianopic Dyslexia, Brain,
1995

• LVFD oculomotor changes
• Smaller amplitude of long saccade to left
• Normal subjects 14 degree
• LVFD subjects 9.4 degree
• Increase in number of saccades to left
• Increase in number of repetitions of saccades to
  left

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How would this oculomotor deficit affect reading
performance?
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How would this oculomotor deficit affect reading
performance?

• Cause person to skip lines or
• Begin reading in middle of line
• Reduce reading speed
• Poor page navigation
• Decreased comprehension

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• RVFD oculomotor changes
• Significantly longer fixation durations
• Increased of regressive saccades
• Increased of repetitions in saccades to the
  right
• smaller amplitude of saccades to the right

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How would this oculomotor change affect reading
performance?
33
How would this oculomotor change affect reading
performance?

• Cause omission of endings of words
• Leading to misidentification or spelling of words
• Poor page navigation
• Significantly reduced reading speed
• And reading comprehension

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Reading DeficitsRight vs. Left

• Persons with RVFD read 3x more slowly than norms
• Reading saccades are more disorganized
• Persons with LVFD read 2x more slowly than norms
• Greatest difficulty locating beginning of text
  line
• Both groups have particular difficulty with
  numbers
• No context to check accuracy

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Additional Factors in Reading Performance

• Difficulty using/adapting to bifocal
• Experience blurry vision due to increased eye
  movement
• Often need single lens reading glasses
• Presence of hemi-inattention
• Increases errors especially omissions to left
• Presence of aphasia-language deficit
• Short term memory loss
• Other disruptions in concentration

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Reduced Eye Hand CoordinationWriting

• Legibility is reduced
• Drift up or down
• on line
• Write on top of
• other words
• Position incorrectly

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ADL Challenges Caused by VFD

• The daily activities affected are those that
• Depend on vision to complete the task
• Require monitoring of a wide visual field
• Require interaction with a dynamic visual field

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ADL Challenges(in descending order)

• Driving
• Shopping and community events
• Yard work
• Meal preparation
• Financial management
• Functional communication
• Calendars, telephones, clocks, TV viewing
• Housekeeping
• Selfcare
• Limited problems with grooming, clothing selection

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Emotional Impact

• Anxiety in crowded or dynamic environments
• Patient described as Crowd-it is
• Unable to process sufficient visual input for
  safety
• CNS sounds alarm through autonomic system
• Person experiences SOB, rapid heart rate,
  sweating, nausea
• Loss of self confidence
• Experiences many many embarrassing mistakes
• Increase in passivity
• Feels more comfortable with others leading
• Social isolation
• Doesnt tolerate change

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Occupational Therapy Assessment
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Quantification of the Deficit

• Spontaneous recovery will not occur for most
  patients
• Therefore compensation is the primary approach in
  therapy
• To teach compensatory strategies, must know
  location and extent of the VFD

42
Clinical Observations

• Suggest the presence and location of the deficit
• biVABA clinical observation sheet
• Observations can be made during ADLs
• Compare observations with team members to look
  for consistencies in behavior that suggest
  presence and location

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Clinical ObservationsFrom Brain Injury Visual
Assessment Battery for Adults

• Observe the client move through crowded areas
  with moving obstacles
• Collides or comes very close to obstacles
  consistently on one side
• Stares straight ahead at the floor immediately in
  front of him/her
• And/or consistently stares to one side
• Stays very close to one side of the wall when
  ambulating down a hallway
• Uses fingers to trail wall to tactually guide
  self
• Refuses to take the lead when ambulating,
  preferring to walk behind others
• Appears anxious or uncertain in crowded areas
• Stops walking when approaching or passing by
  another moving person or objects
• Complains of feeling off balance particularly to
  one side

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Clinical Observations cont

• Observe pt reading out loud a paragraph of 10
  point print on 8.5-11 paper
• Transforms words by omitting or misreading
  letters on one side of words
• Abbreviates scan to one side of page, omitting
  words on that side
• Uses finger to direct scan across the line of
  print and maintain place on the page
• Consistently loses place on one side of the page
• Hesitates reading a word, or misreads a word
  initially then corrects self reads very slowly

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Clinical Observations cont

• General observations
• Avoids crowds and crowded environments such as
  shopping centers
• Complains of disorientation when riding in a car
  or wheelchair
• Reads only half of a wide sign or misses signage
  on one side
• Transforms numbers. Example reads an 8 as a
  6or 3
• Displaces handwriting to one side when completing
  a form such as a check
• Handwriting drifts up and down when writing on
  line or addressing an envelope

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• General Observations continued
• Complains of being unable to follow what is
  happening on TV particularly when viewing
  sporting events or shows with a lot of action
• Makes mistakes dialing a telephone, such as
  pressing a similar but incorrect number
• Scans shelves or counters very slowly to find
  items and often is unable to locate an item
• Has become very particular that items be returned
  to a specific location following use and becomes
  upset with others who leave items out or return
  them to a different location

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Standardized Assessments

• Ideal Automated perimetry or evaluation by an
  ophthalmologist or optometrist
• Challenges
• Limited access
• Patient may not have physical or attentional
  capability for assessment
• Reality Must rely on combination of standardized
  clinical assessments and observation

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AAO Red Dot Confrontation Test

• Test Materials
• Basic Visual Function Assessment form
• Targets (2 red dots placed on 2 tongue
  depressors-one dot on each side of one end of the
  stick)
• Occluder (eye patch)
• Test Environment
• Well lighted room, light source behind pt
• Free from visual, auditory and physical
  distractions

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• Procedure
• Pt is seated with eyeglasses OFF
• EX sits directly across and 1 meter from pt
• To test right eye
• Occlude pts left eye
• Instruct pt to focus on EX left eye
• EX closes right eye to ensure he/she has same
  visual field experience as pt
• EX present both targets simultaneously to pt, in
  location A, then B, then C, then D
• Targets must be held 20 inches from client to
  enable both targets to be seen in the unimpaired
  field
• If targets are held too close to the pt, the pts
  nose may occlude one of the targets causing an
  invalid test
• If you cannot see both targets, the pt will not
  be able to see both targets
• Note whether pt sees both targets
• If pt sees both targets, ask whether the 2 dots
  are equally bright

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AAO Red Dot Confrontation Test
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Position A level with top of forehead
directly above outside edge of
shoulder Position B Level with Adams apple at
the outside edge of the shoulders Position
C Level with forehead, adjacent to temples of
face Position D Level with Adams
apple, adjacent to the jaw line of
face Position E (hold targets horizontally) one
target level with brow line other target level
with chin
Target Locations
Occluded eye
Occluded eye
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Scoring
Scoring Key target seen - target not
seen D target seen but color is diminished


-
-
D
D


-
-
Scoring indicates presence of left hemianopsia in
the left eye
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Kinetic Two Person Confrontation Test

• Test materials
• Basic Visual Function Assessment form
• Patch occluder
• Penlight
• Interesting target, large enough to be seen at 1
  meter distance without eyeglasses
• Environment
• Dim illumination to enhance visibility of
  penlight illumination must be sufficient for EX
  to view patients eye for movement during
  fixation. Room should be free from distractions

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Test Procedure

• The patient is seated comfortably with eyeglasses
  off
• One EX sits directly across and approximately 1
  meter
• from the patient. Other EX holds the penlight
  and stands
• behind the patient.

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Test Procedure cont

• Occlude one eye
• Instruct patient to fixate on the target held by
  the front EX. (EX holds target at patients eye
  level)
• As patient fixates on target, rear EX brings
  lighted penlight from behind the patient to the
  front moving slowly in an arc
• The patient is instructed to indicate as soon as
  the penlight is seen
• Front EX observes patients eye during the exam
  to ensure patient does not look for the penlight
• Rear EX notes location that patient sees the
  penlight and records it on the form

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Scoring
X
Horizontal Plane (3 and 9 oclock positions) EX
indicates location on arc X where patient first
notices penlight
Occluded eye
Occluded eye
X
Vertical Plane (12 and 6 oclock positions) EX
indicates location on arc X where patient first
notices penlight
X
X
X
X
Patient with left homonymous hemianopsia