Metamorphopsia

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Metamorphopsia

• Scotoma is too big to complete perceptually
• Objects appear warped or misaligned

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Preferred Retinal Locus (PRL)

• If scotoma covers fovea, CNS adopts an eccentric
  retinal area to act as a pseudo-fovea for visual
  tasks previously completed by the fovea
• Develops within 24 hours of loss of fovea

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40 place PRL above the scotoma on the
retina(leaves lower portion of field clear)
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35 place PRL to the right (leaves left side of
page clear)
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20 place PRL to left
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7 place PRL below
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• Person may develop more than one PRL and use a
  different one depending on task and lighting
  conditions
• Ability to use PRL to direct eye movements is
  more highly correlated to reading ability than
  other visual function
• Although person develops PRL, he/she may not be
  aware of it
• Important to assess ability to use PRL

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Peripheral Visual Field Deficit

• Person also exercises perceptual completion
• May be completely unaware of deficit
• Will not interfere with perception of visual
  details (acuity)
• But will affect mobility
• Reduces detection of motion and form

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Ability of optic nerve to transmit visual input

• Can be damaged by disease, trauma and congenital
  conditions
• Glaucoma
• Optic neuritis
• Head injury
• Can lose all or part of field
• Depending on location, extent of damage

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Deficits in Posterior Visual System
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Visual Field Deficits

• Lesions along geniculocalcarine tracts or in
  occipital lobe
• Most common cause in adult is stroke
• Posterior cerebral artery (PCA)
• Pure visual stroke (sometimes affects language)
• Middle cerebral artery (MCA)
• Mix of motor, sensory, visual, cognitive
• Lesion behind LGN will always cause homonymous
  loss

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Homonymous Hemianopsia
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Hemianopsia with Macular Sparring
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Cortical Blindness

• Also called cortical visual impairment
• CVI
• Damage is so significant in occipital lobe, CNS
  is not able to complete any cortical processing
  of vision

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Person loses
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Person loses

• Object identification through visual system
• Visual orientation to space
• Cognitive application of vision

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Person retains
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Person retains

• Subcortical processing of vision
• Navigational vision
• Vision for safety
• Other sensory processing
• Haptic discrimination
• Auditory discrimination

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Alteration of Visual Attention

• Difficulty arousing attention
• Difficulty attending globally
• Difficulty attending to details
• Difficulty sustaining attention
• Difficulty dividing/shifting attention
• Asymmetrical attention
• Unilateral spatial neglect

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Diminishment of Attention

• Has pervasive effect on cognition
• Person takes in information in incomplete
  disorganized fashion
• CNS cannot properly analyze incoming information
• Decision making is based in incomplete and/or
  incorrect information
• Garbage in - garbage out