Which visual field defect is typically the earliest detectable abnormality on automated perimetry in primary open-angle glaucoma?
- A Nasal step along the horizontal meridian ✓
- B Temporal wedge-shaped sector defect
- C Central scotoma involving fixation
- D Generalised concentric constriction
Correct answer: A. Nasal step along the horizontal meridian
Explanation
Glaucomatous damage respects the horizontal raphe, so the earliest perimetric loss is a small paracentral depression extending to but not crossing the horizontal meridian, producing a nasal step, usually superior. Arcuate Bjerrum scotomas follow as nerve fibre bundle damage progresses. Central fixation is spared until late, temporal wedges suggest chiasmal pathology, and concentric constriction points to retinal degeneration or end-stage disease rather than early glaucoma.
Reference: Khurana AK, Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.