A 52-year-old man has a dense central scotoma in the right eye and a superotemporal visual field defect in the left eye, with a normal left optic disc. The combination localizes the lesion to the:
- A Anterior chiasm at the junction with the right optic nerve ✓
- B Right optic tract
- C Left occipital cortex
- D Posterior chiasm involving the crossing macular fibres bilaterally
Correct answer: A. Anterior chiasm at the junction with the right optic nerve
Explanation
This is a junctional scotoma, produced by a lesion at the anterior angle of the chiasm on the side of the central scotoma. It damages the right optic nerve fibres including the macular bundle, giving the right central scotoma, and also the lower crossing nasal fibres from the left eye that loop forward into the right optic nerve as Wilbrand's knee before turning back, giving the left superotemporal defect. An optic tract lesion would produce an incongruous contralateral homonymous hemianopia instead.
Reference: Parsons' Diseases of the Eye, 23rd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.