Question at position 38 EXTRA CREDIT (1pt): Which of the following lesions would result in the depicted visual field deficit? ABCDClear my selectionSingle choice
A
A
B
B
C
C
D
D

Question

Question at position 38 EXTRA CREDIT (1pt): Which of the following lesions would result in the depicted visual field deficit? ABCDClear my selection

BlackTom AI · Accepted Answer

The finding is a contralateral homonymous hemianopia: both eyes have lost the same half of the visual field (the left visual field), which indicates a post‑chiasmal lesion on the right side — specifically the right optic tract at location C.

1) Relevant knowledge points and concepts
- Each visual hemifield projects to the contralateral cerebral hemisphere: the left visual field is represented in the right hemisphere, the right visual field in the left hemisphere.
- Nasal retinal fibers cross at the optic chiasm; temporal retinal fibers remain uncrossed. After the chiasm the bundled fibers are called the optic tracts; each optic tract carries information about the contralateral visual field from both eyes.
- Lesions anterior to the chiasm produce monocular defects; lesions at the chiasm classically produce bitemporal (heteronymous) hemianopia; lesions in the optic tract, LGN, optic radiations, or visual cortex produce contralateral homonymous hemianopia.

2) Step‑by‑step reasoning
- The diagram’s paired visual fields show loss of the same side (left) in both eyes → this is a homonymous hemianopia.
- Because the lost half is contralateral to the lesion (left field lost → lesion is in right visual pathway after the chiasm), the lesion must be on the right side, post‑chiasm.
- The optic tract (label C on the diagram) contains fibers from the right hemisphere representing the left visual field (temporal retina of the right eye + nasal retina of the left eye). Damage there abolishes left field vision from both eyes, producing the depicted deficit.

3) Intermediate mapping steps
- Left visual field → nasal retina of left eye + temporal retina of right eye.
- Nasal fibers from left eye cross at the chiasm to join temporal fibers from the right eye → these combined fibers travel in the right optic tract.
- Lesion at C (right optic tract) therefore eliminates input carrying the left visual field from both eyes.

4) Why C is correct
- C is the post‑chiasmal structure (right optic tract) whose fibers correspond to the contralateral (left) visual field; lesion here gives the exact homonymous left hemianopia shown.

5) Why other options are incorrect
- A (optic nerve) would cause monocular loss in the ipsilateral eye, not the same half in both eyes.
- B (optic chiasm) classically causes bitemporal hemianopia (loss of both temporal fields), not a homonymous hemianopia.
- D (more posterior cortical/geniculate position depending on the diagram) could produce homonymous defects but the labeled location D on this figure does not correspond to the optic tract explaining the specific pattern — the diagram’s C is the anatomically correct post‑chiasmal site.

Conclusion: The visual field deficit is caused by a lesion at C (the right optic tract), so the correct answer is C.

Question at position 38 EXTRA CREDIT (1pt): Which of the following lesions would result in the depicted visual field deficit? ABCDClear my selectionSingle choice

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