A 70-year-old hypertensive man has a dense left homonymous hemianopia, yet his visual acuity is 6/6 in both eyes and he can read the central chart normally. CT shows a right occipital infarct. The preservation of central vision is best explained by:

• A Sparing of the calcarine artery territory by collateral branches of the anterior choroidal artery
• B Macular fibres projecting to the lateral geniculate body rather than the cortex
• C Compensatory expansion of the ipsilateral visual cortex
• D Dual blood supply to the occipital pole from the posterior cerebral and middle cerebral arteries ✓

Explanation

Macular sparing in a homonymous hemianopia localises the lesion to the occipital cortex. The occipital pole, which represents central vision, receives supply from the posterior cerebral artery and terminal branches of the middle cerebral artery, so embolic PCA occlusion spares fixation. Macular sparing does not occur with optic tract, lateral geniculate or optic radiation lesions because those structures have no such dual arterial supply.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.