A focal lesion to the calcarine cortex typically produces which type of visual field deficit, and what explains macular sparing in some PCA strokes?

• A. Contralateral homonymous field defect; macular sparing due to dual blood supply from MCA and PCA to the occipital pole
• B. Bilaterally blindness
• C. Ipsilateral hemianopia
• D. Vertical diplopia

Answer: (A)

Damage to the calcarine cortex, the primary visual cortex in the occipital lobe, disrupts the processing of the opposite visual field in both eyes. Since each hemisphere handles the contralateral visual field, a lesion on one side produces a contralateral homonymous field defect. The macula—the center of our vision—maps to the occipital pole and often remains functional in some PCA strokes because that region receives blood from two arterial sources: branches of both the posterior cerebral artery and the middle cerebral artery. When the PCA territory is compromised but the MCA supply is still intact, the central vision can be spared while the peripheral visual field is lost, leading to macular sparing.