A 47-year-old woman with a left temporal lobe glioma reports difficulty seeing objects in the lower right visual field of each eye. Formal perimetry confirms loss confined to the upper right quadrant bilaterally. Which structure has been interrupted?
- A Left optic tract
- B Meyer's loop in the left temporal lobe ✓
- C Left parietal optic radiation
- D Left calcarine cortex, inferior bank
Correct answer: B. Meyer's loop in the left temporal lobe
Explanation
Fibres from the inferior retinal quadrants sweep forward into the temporal lobe as Meyer's loop before turning back to the primary visual cortex. A left-sided lesion therefore removes the contralateral upper quadrant, the so-called pie-in-the-sky defect. The parietal radiation carries superior retinal fibres and would give an inferior quadrantanopia, while an optic tract lesion produces a complete incongruous hemianopia affecting both fields of one side, not a single quadrant.
Reference: Snell's Clinical Neuroanatomy, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.