Automated perimetry in a 60-year-old man shows a dense upper paracentral depression arching around fixation and terminating sharply at the horizontal meridian nasally, with a matching inferior nerve fibre bundle defect. Cup-to-disc ratio is 0.8 with a focal inferior rim notch. This pattern of field loss indicates damage along which anatomical structure?

• A Optic radiations
• B Lateral geniculate body
• C Retinal nerve fibre layer converging on the optic disc ✓
• D Chiasmal crossing fibres

Explanation

Glaucomatous defects are nerve fibre bundle defects that respect the horizontal raphe because retinal ganglion axons arcuate around the fovea and never cross it. A Bjerrum or arcuate scotoma ending at the horizontal meridian, often with a nasal step, therefore localizes to the retinal nerve fibre layer and optic nerve head. Post-chiasmal lesions produce hemianopic defects that respect the vertical meridian, which distinguishes them cleanly from this pattern.

Reference: Kanski's Clinical Ophthalmology, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.