What visual field defect is most characteristic of a stroke affecting the blood supply from the Posterior Cerebral Artery (PCA)?

Homonymous Hemianopia is the Most Characteristic Visual Field Defect of PCA Stroke

A stroke affecting the blood supply from the posterior cerebral artery (PCA) most characteristically causes a contralateral homonymous hemianopia 1, 2. This visual field defect occurs due to damage to the visual cortex in the occipital lobe, which receives its blood supply primarily from the PCA.

Anatomical Basis and Characteristics

The posterior cerebral artery supplies:

• Primary visual cortex (calcarine cortex) in the occipital lobe
• Parts of the temporal lobe and thalamus
• Portions of the midbrain

When a PCA stroke occurs:

• The resulting homonymous hemianopia affects the same half of the visual field in both eyes
• The defect is contralateral to the side of the lesion (e.g., right PCA stroke → left visual field defect)
• The defect may be complete or partial (quadrantanopia) depending on the extent of the infarct

Specific Visual Field Defect Patterns

1. Complete homonymous hemianopia - Most common pattern with extensive PCA territory involvement 1, 3

2. Homonymous quadrantanopia - Partial involvement of the visual cortex:

   • Superior quadrantanopia - Damage to inferior calcarine cortex
   • Inferior quadrantanopia - Damage to superior calcarine cortex 4, 5

3. Macular sparing - Often seen in PCA strokes due to:

   • Dual blood supply to the occipital pole (from middle cerebral artery)
   • Representation of central vision in the posterior 25% of visual cortex 4

Clinical Presentation and Assessment

Patients with PCA stroke and homonymous hemianopia typically present with:

• Sudden, painless visual field loss
• Difficulty seeing objects in the affected visual field
• Problems with reading (particularly finding the beginning of the next line)
• Bumping into objects on the affected side
• Possible unawareness of the visual deficit 2

In a study of 85 patients with PCA stroke, 87% reported negative visual sensations (absence of vision) rather than positive phenomena, and 66% correctly identified that the visual loss affected the same side in both eyes 3.

Diagnostic Evaluation

• Visual field testing is highly accurate (96%) in predicting the side of the visual cortex lesion in PCA stroke 5
• Automated perimetry is more sensitive than confrontation testing at the bedside 1
• MRI of the brain is the gold standard for confirming the diagnosis and determining the extent of the infarct 1

Associated Findings

PCA strokes may also present with additional symptoms depending on the extent of involvement:

• Thalamic involvement: sensory symptoms (numbness, tingling) 3
• Temporal lobe involvement: memory deficits
• Midbrain involvement: oculomotor abnormalities
• Top of basilar syndrome: somnolence, hallucinations, and eye movement disorders 1

Management Considerations

For patients with homonymous hemianopia from PCA stroke:

• Acute stroke management per standard protocols 1
• Visual rehabilitation approaches:
  • Scanning training to improve compensatory eye movements 2, 6
  • Peripheral prism glasses to expand the visual field 2
  • Visual field restitution therapy (though evidence is limited) 6

Pitfalls and Caveats

1. PCA strokes can be missed or delayed in diagnosis because:

   • NIHSS may underestimate posterior circulation strokes 1
   • Patients may present with non-specific symptoms (headache, dizziness) 1
   • Visual field defects may be attributed to ocular rather than cerebral pathology

2. Homonymous hemianopia should be distinguished from:

   • Heteronymous hemianopia (affecting opposite halves of visual fields)
   • Monocular visual loss (suggesting anterior visual pathway pathology) 2

3. The pattern of visual field loss correlates well with the location of the lesion, but quadrantic defects sometimes underestimate the extent of cortical damage 5.

Remember that early recognition and appropriate management of PCA stroke is critical for optimizing outcomes and implementing appropriate visual rehabilitation strategies.