Visual Pathway and Visual Fields

Introduction

• Discusses the visual pathway from when light hits the retina.
• Importance of watching the photo transduction cascade video for foundational understanding.
• Covers the process through the optic nerve and beyond.

Visual Fields and Retinas

• Each eye has a visual field: left and right visual fields.
• Visual fields are divided into nasal and temporal components:
  • Nasal visual field: near the nose.
  • Temporal visual field: near the temples.
• Each eye's visual field is split into two:
  • Right eye: left and right visual fields.
  • Left eye: left and right visual fields.

Retinal Components

• Temporal Hemiretina:
  • Comes from the left visual field in the right eye.
  • Information stays ipsilateral (same side).
• Nasal Hemiretina:
  • Comes from the right visual field.
  • Information crosses to the contralateral side (opposite side) at the optic chiasm.

Pathway of Visual Information

• Optic Nerve: Carries visual information from each eye.
• Optic Chiasm: Where optic nerves partially cross.
• Optic Tract: Carries information post-chiasm.
  • Right optic tract: carries info from left visual field.
  • Left optic tract: carries info from right visual field.

Lateral Geniculate Nucleus (LGN)

• Located in the thalamus.
• Has 6 layers:
  • Ipsilateral fibers go to layers 2, 3, 5.
  • Contralateral fibers go to layers 1, 4, 6.
• Some fibers project to midbrain structures like the superior colliculus and pretectal nuclei.

Optic Radiations

• Superior Retinal Fibers (Barum's Loop): Go through the parietal lobe.
• Inferior Retinal Fibers (Meyer's Loop): Go through the temporal lobe.
• They carry information to the striate cortex of the occipital lobe, the primary visual cortex.

Lesions and Visual Deficits

1. Lesion #1: Damages optic nerve, results in right-sided monocular blindness.
2. Lesion #2: Pituitary tumor compressing optic chiasm, causes bitemporal hemianopia.
3. Lesion #3: Compression of outer optic chiasm, leads to binasal hemianopia.
4. Lesion #4: Damage to right optic tract, results in left homonymous hemianopia.
5. Lesion #5: Damage to Barum's Loop, results in left inferior quadrantanopia.
6. Lesion #6: Damage to Meyer's Loop, results in right superior quadrantanopia.
7. Lesion #7: Damage to entire optic radiation, causes left homonymous hemianopia.
8. Lesion #8: Damage in occipital lobe, usually involves posterior cerebral artery, can spare macular vision due to middle cerebral artery supply, results in left homonymous hemianopia with macular sparing.

Conclusion

• Visual pathway intricacies and associated deficits emphasize the importance of specific knowledge of neurological pathways and potential clinical correlations.