VFD Lecture Part One

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VFD Lecture Part One
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Evaluation and Treatment of Visual Field Deficits
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Lecture Objectives

• Correlates lesion site with specific VFD
• Describes changes in occupational performance
  caused by VFD
• Describes adjustment related to VFD
• Describes treatment intervention for specific
  performance deficits
• Demonstrates correct testing procedure and
  interpretation

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The Visual Field

• Area of visual world that can be seen
• when looking straight ahead

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The Visual Field cont

• Captured initially by the retina
• Mapped out in several areas of CNS during visual
  processing
• Superior colliculi
• Lateral geniculate nucleus
• Geniculocalcarine tracts
• Occipital pole

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Sensitivity of visual field is mapped out as a
field diagram
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Geographic Markers

• Divided into quadrants
• with fovea in the center
• Superior and inferior
• Nasal and temporal
• Lateral crescent
• Crescent shaped area
• marked by dotted line

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Sensitivity Markers
Central field fovea and macula
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Sensitivity Markers
Peripheral or paracentral field
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Sensitivity is mapped out as an isopter

• Defines the hill of vision
• Provides a 3-D map of
• visual sensitivity
• Isopters depict boundary
• between region where the
• target is visible and where
• it is not visible

isopters
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The Visual Field is Binocular
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Visual field deficit is the most common visual
impairment following brain injury
Most VFD results from lesions along
genicul- calcarine tract (GCT) or in occipital
pole (OP) Most result from posterior cerebral
artery occlusion (PCA) Middle cerebral artery
occlusion can also cause
GCT
OP
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PCA Lesion

• 75 result in homonymous hemianopsia
• 70 with complete hemifield impairment

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• Macular field sparring may occur in 30

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Other Causes of Visual Field Deficits

• Anoxia
• Can create bilateral field constriction (tunnel
  vision)
• Central retinal artery occlusion
• Glaucoma
• Multiple sclerosis

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Perimetry Testing

• All testing involves three components
• Sustained fixation on a central target
• Presentation of a second target of a specified
  size/luminosity in a designated area of the field
• Acknowledgment of the second target without
  breaking fixation on the central target

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Testing Defines the Visual Sensitivity of the
Field

• Every point within the retinal visual field has a
  specific visual threshold
• Defined as the weakest test stimulus just visible
  in that location under the specific test
  conditions
• Indicates the sensitivity of the photoreceptors
  to stimuli
• Mapped out as isopters
• Threshold levels vary within the field
• Hill of vision concept
• Lowest at the fovea
• Highest at the periphery

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Circles represent isopters in the field diagram
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Static vs Kinetic Test Strategy

• Static
• Target appears in a specified location without
  moving to that location
• Kinetic
• Target is moved into a specified area of the
  field until it is detected and acknowledged

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Threshold vs. Screening Test Strategy

• Threshold
• target is presented in specific location in field
  and increased in intensity until it becomes
  visible
• Very accurate, discrete measurement
• Screening
• Target is presented one time at supra-threshold
  value

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Various Perimetry Tests

• Screening
• Confrontation test
• Manual
• Tangent screen
• Damato campimeter
• Bowl (measure central and peripheral)
• Automated Humphrey Visual Field Analyzer
• Manual Goldmann perimeter
• Real Time
• Scanning laser ophthalmoscope
• Macular field only

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Screening Confrontation Tests
Red Dot Test
Finger Confrontation

• Quick bedside maneuver
• Provides gross indication of deficit
• Estimate how much field is missing based on
  comparison
• to examiners field
• Unreliable

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Manual Perimeters
Tangent Screen

• Quick and inexpensive
• Requires skilled examiner
• Measures only central
• field

Damato Campimeter

• Portable
• Reliable
• Measures only central
• field

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Bowl Perimeters
Humphrey Visual Field Analyzer
Goldmann Manual Bowl Perimeter
Patient
Examiner

• Central and peripheral field
• Accurate, comprehensive
• Picks up subtle deficits
• Field diagram easy to interpret
• Not readily available

• Central and peripheral field
• Requires skilled examiner
• Field diagram drawn in isopters
• Not readily available

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Real Time Perimetry
Scanning Laser Ophthalmoscope

• Images retina in real time
• using Hene laser
• Allows discrete measurement
• of scotomas 5 degrees or less
• Most reliable, accurate form
• of perimetry
• But only measures central
• 20 degrees of field

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Interpretation of Visual Field Testing

• Different pathologies are characterized by losses
  in different areas of the field
• Central scotomas
• Paracentral scotomas
• Peripheral losses
• Hemianopsias, quadrantanopsias
• Also characterized by denisity
• Absolute
• completely non functioning retina
• Relative or threshold
• Retina still has some capability for function

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Interpretation of Perimetry Tests

• Visual field is plotted on a field diagram
• Visual field degrees 60 superiorly, 75
  inferiorly, 100 temporally, 60 nasally
• Diagrams come in different formats
• Isopters
• Absolute scale
• Gray scale

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Isopter Diagram
isopter
Seen area

• Isopter boundary between a region where a target
  is visible and where it is not visible
• Functioning retina lies inside the isopter

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Absolute Scale Diagram

• Uses symbols to describe sensitivity of field
• One symbol indicates loss
• Another symbol indicates decreased sensitivity
• Each perimeter will have its own legend

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Gray Scale Diagram

• Sensitivity of field is described using different
  shades of gray
• Light shadinghigh threshold, can detect small
  target
• Black shadingno response to target

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• Threshold tests
• Will have several isopters or symbols
• Depicting varying sensitivity of the field
• Screening tests
• Will have one isopter or one set of symbols
• Depict only areas of intact and impaired retinal
  function