Question

Homonymous hemianopia may occur due to lesion involving

• A. Optic nerve
• B. Optic chiasm
• C. Optic tract
• D. Bilateral foveal lesions

Hint:

Fibers from matching halves of both eyes are already grouped together just behind the chiasm.

Answer 1

The Correct Option is C

This question asks which point along the visual pathway, when damaged, causes a homonymous hemianopia, the same-side field loss in both eyes.

1. Optic nerve: A lesion here, before the chiasm, affects only that one eye's vision, not a matching field defect in both eyes.
2. Optic chiasm: This is where nasal retinal fibers cross, so damage here classically causes bitemporal hemianopia, not homonymous hemianopia.
3. Optic tract: Just behind the chiasm, fibers from corresponding halves of both eyes have already regrouped together, so a lesion here classically produces homonymous hemianopia.
4. Bilateral foveal lesions: These affect central vision in both eyes rather than causing a one-sided field defect.

Based on the standard organization of the visual pathway, the optic tract is the site whose damage produces a homonymous hemianopia.

Note: the source paper's printed answer key marks the optic chiasm as correct, but the chiasm is where fibers cross to classically cause bitemporal hemianopia; the optic tract, just behind the chiasm, is the site that produces homonymous hemianopia by standard neuroanatomy. This solution follows the medically correct answer and flags the discrepancy for review.

Let's summarize:

• Optic nerve lesions affect one eye only; chiasm lesions cause bitemporal loss.
• Optic tract lesions, where matching fibers from both eyes have already regrouped, cause homonymous hemianopia.

So a lesion of the optic tract produces homonymous hemianopia.