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Visual Field Defects

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The Visual Field

Overview

The visual pathway describes the route impulses travel from the retina to the brain. When light hits the retina, the temporal field hits the nasal retina and the nasal field hits the temporal retina. The overall route is from the retina, through the optic nerve, to the optic chiasma (where the nasal retina (and the temporal visual field) crosses over to the opposite side, the temporal retina (nasal visual field) stays in place), then to the optic tract, then the lateral geniculate nucleus, then the primary visual cortex.

Visual Field Defects

Overview

  • Visual field defects can be divided into:
    • Lesions before the optic chiasm – ipsilateral visual field defects
    • Lesions at the optic chiasm – bitemporal visual field defects
    • Lesions after the optic chiasm – contralateral visual field defects

Lesions before the optic chiasm

  • Cause visual field defects in the ipsilateral eye
  • Optic nerve damage causes central and unilateral visual field defects (monocular blindness)
  • Causes include optic neuritis, amaurosis fugax, and trauma

Lesions at the optic chiasm

  • Bitemporal hemianopia worse in the upper visual field:
    • Due to lesions in the optic chiasm that spread up from below, classically a pituitary tumour
  • Bitemporal hemianopia worse in the lower visual field:
    • Due to lesions in the optic chiasm that spread down from above, classically a craniopharyngioma

Lesions after the optic chiasm

  • Lesions lead to problems on the contralateral side due to image reversal (temporal visual field light hits the nasal retina, and nasal visual field light hits the temporal retina):
  • Homonymous hemianopia:
    • Complete homonymous hemianopia without macular sparing:
      • Due to lesions in the main optic radiation/optic peduncle
      • Causes include middle cerebral artery (MCA) strokes
    • Complete homonymous hemianopia with macular sparing:
      • Due to lesions in the anterior visual cortex
      • Causes include posterior cerebral artery strokes
  • Homonymous quadrantanopia:
    • Upper homonymous quadrantanopia:
      • Due to lesions in the temporal radiation
    • Inferior homonymous quadrantanopia:
      • Due to lesions in the parietal optic radiation
      • Remembered using PITS – parietal inferior and temporal superior

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