Overview
This lecture covers the types and features of visual field defects resulting from lesions at different levels of the visual pathway, including definitions and key clinical presentations.
Inverted and Reversed Visual Fields
- The superior visual field projects onto the inferior retina; the inferior field projects onto the superior retina.
- The temporal visual field projects onto the nasal retina, and the nasal field projects onto the temporal retina.
- "Inverted and reversed" refers to this relationship between visual fields and retinal mapping.
Definitions: Homonymous and Congruent/Incongruent Defects
- Homonymous defects affect the same side of the visual field in both eyes (right or left).
- Congruent defects are similar in both eyes; incongruent defects differ between the two eyes.
Lesions and Their Effects
Optic Nerve Lesion
- Results in complete blindness of the affected eye.
- Ipsilateral direct and contralateral consensual light reflexes are lost.
Junctional Scotoma
- Lesion at the optic nerve near the chiasm affects the Wilbrand's knee.
- Causes total blindness on the affected side and upper temporal field defect in the opposite eye.
Optic Chiasm Lesions
- Central chiasmal lesion affects crossing nasal fibers, causing bitemporal hemianopia.
- Lateral chiasmal lesion affects uncrossed temporal fibers, causing binasal hemianopia.
- Both may cause partial optic atrophy and selective pupillary reflex loss.
Optic Tract Lesion
- Causes contralateral homonymous hemianopia, typically incongruent.
- Leads to hemianopic pupillary response (Wernicke's pupil) and possible optic atrophy.
Lateral Geniculate Body Lesion
- Also causes contralateral homonymous hemianopia (incongruent), but pupillary reflexes are spared.
- May show partial optic atrophy.
Optic Radiation Lesions
- Temporal lobe (Meyer's loop) lesion causes contralateral superior quadrantanopia ("pie in the sky").
- Parietal lobe (Baum's loop) lesion causes contralateral inferior quadrantanopia ("pie on the floor").
- If all fibers are affected, results in incongruent homonymous hemianopia with no pupillary reflex loss.
Visual Cortex Lesions
- Posterior cerebral artery stroke causes contralateral congruent homonymous hemianopia with macular sparing.
- Occipital tip lesions (trauma) cause contralateral congruent homonymous macular defects.
- No optic atrophy or pupillary reflex abnormalities in cortical lesions.
Key Terms & Definitions
- Homonymous — Same side visual field loss in both eyes.
- Congruent defect — Identical visual field loss in both eyes.
- Incongruent defect — Differing visual field loss between eyes.
- Junctional scotoma — Total blindness on one side and upper temporal defect on the opposite.
- Bitemporal hemianopia — Loss of temporal (outer) visual fields in both eyes.
- Binasal hemianopia — Loss of nasal (inner) fields in both eyes.
- Wernicke's pupil — Hemianopic pupillary response after optic tract lesion.
- Macular sparing — Central vision preserved despite homonymous hemianopia.
Action Items / Next Steps
- Review anatomy and blood supply of the visual pathway.
- Study diagrams relating lesion location to specific visual field defects.
- Memorize key terms and classic field loss patterns for exams.