A 48-year-old woman reports progressive dimness of vision in her left eye over 8 months. Visual field testing shows a dense central scotoma in the left eye together with a subtle superotemporal field defect in the right eye. Where is the lesion?
- A Left lateral geniculate body
- B Anterior chiasm at the junction of the left optic nerve and chiasm ✓
- C Right occipital cortex
- D Optic radiations in the left temporal lobe
Correct answer: B. Anterior chiasm at the junction of the left optic nerve and chiasm
Explanation
An ipsilateral central scotoma combined with a contralateral superotemporal defect is the junctional scotoma, produced by a lesion at the anterior angle of the chiasm where crossing fibres from the inferonasal retina of the opposite eye loop forward into the optic nerve (Wilbrand's knee). A pituitary adenoma within the chiasm produces symmetric bitemporal defects without an ipsilateral central scotoma. Postgeniculate lesions give congruous homonymous defects that never produce a monocular scotoma.
Reference: Kanski's Clinical Ophthalmology, 9th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.