A 62-year-old man has a left homonymous hemianopia in which the macular region is spared. The anatomical basis for this macular sparing is best explained by:

• A Sparing of the calcarine cortex because it lies outside the middle cerebral artery territory
• B Bilateral cortical representation of the macula at the occipital pole ✓
• C Decussation of macular fibres within the optic chiasm
• D Projection of macular fibres to the lateral geniculate body rather than the cortex

Explanation

The macula is represented at the occipital pole, an area of watershed supply between the posterior cerebral artery and terminal branches of the middle cerebral artery. This dual arterial supply, together with the disproportionately large macular representation extending across both hemispheres at the pole, allows survival of macular vision when one posterior cerebral artery is occluded. Option A fails because the calcarine cortex is supplied by the posterior cerebral artery, not the middle cerebral artery.

Reference: Gray's Anatomy for Students, 4th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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