A 45-year-old woman has bitemporal hemianopia on Goldman perimetry. MRI shows a suprasellar mass. The visual field defect results from compression of which structure?
- A Optic tract posterior to the chiasm
- B Lateral geniculate nucleus
- C Decussating nasal fibres of the optic chiasm ✓
- D Meyer's loop in the temporal lobe
Correct answer: C. Decussating nasal fibres of the optic chiasm
Explanation
Bitemporal hemianopia is the hallmark defect of optic chiasm compression. The chiasm contains decussating nasal retinal fibres from both eyes; nasal fibres carry temporal visual field information. Central compression (pituitary adenoma, craniopharyngioma) damages these crossing fibres, producing temporal field loss bilaterally. Optic tract lesions produce homonymous hemianopia. LGN lesions produce contralateral homonymous hemianopia. Meyer's loop lesions produce a superior contralateral quadrantanopia ('pie in the sky').
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.