Visual field testing in a 52-year-old woman shows a dense central scotoma in the right eye together with a superotemporal field defect in the left eye. This junctional scotoma localises the lesion to the:

• A Body of the optic chiasm
• B Left optic tract
• C Junction of the right optic nerve and the chiasm ✓
• D Right occipital cortex

Explanation

At the anterior chiasm, inferonasal fibres from the contralateral eye briefly loop forward into the optic nerve (Wilbrand's knee) before crossing. A compressive lesion at one optic nerve-chiasm junction therefore produces an ipsilateral central scotoma plus a contralateral superotemporal defect. A pure chiasmal body lesion gives symmetric bitemporal hemianopia without a central scotoma, which is the feature that separates this entity and makes it highly localising.

Reference: Miller's Walsh and Hoyt's Neuro-Ophthalmology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.