A 58-year-old man with a 10-year history of poorly controlled hypertension presents with gradual, painless vision loss. Fundoscopy reveals optic disc cupping with a vertical cup-to-disc ratio of 0.8. Intraocular pressure is 28 mmHg in both eyes. Visual field testing shows a superior nasal step defect. What is the most common cause of this visual field defect pattern?

## Most Common Cause of Superior Nasal Step Defect **Key Point:** The superior nasal step is a classic early visual field defect in primary open-angle glaucoma (POAG), reflecting preferential damage to the superior arcuate nerve fiber bundle. ### Pathophysiology of Glaucomatous Visual Field Defects Glaucomatous optic neuropathy causes characteristic patterns of visual field loss that follow the distribution of retinal nerve fiber bundles: | Defect Pattern | Mechanism | Typical Progression | |---|---|---| | Superior nasal step | Early arcuate damage (superior bundle) | Expands inferiorly and nasally | | Arcuate defect | Continued arcuate bundle loss | May progress to altitudinal | | Altitudinal defect | Horizontal disc ischemia | Advanced glaucoma | | Central scotoma | Optic nerve head involvement | Late-stage disease | **High-Yield:** The **superior nasal step** is the *most common early glaucomatous defect* because the superior arcuate nerve fiber bundle is most vulnerable to elevated intraocular pressure. ### Why POAG in This Case? 1. **Elevated IOP** (28 mmHg) with optic disc cupping (CDR 0.8) 2. **Painless, gradual vision loss** — characteristic of POAG, not acute angle closure 3. **Hypertension history** — risk factor for POAG 4. **Superior nasal step** — pathognomonic early glaucomatous pattern 5. **Bilateral potential** — POAG is typically bilateral **Clinical Pearl:** The nasal step occurs because the nasal retina has thinner nerve fiber bundles and is more susceptible to pressure-induced damage than the temporal retina. ### Differential Defect Patterns - **Pituitary adenoma** → bitemporal hemianopia (chiasmal compression) - **Posterior communicating artery aneurysm** → superior temporal quadrantanopia or bitemporal hemianopia (depending on location) - **Optic neuritis** → central scotoma, not nasal step **Mnemonic:** **NASAL STEP = GLAUCOMA** — Remember: Nasal step is the signature of glaucomatous optic neuropathy. [cite:Harrison 21e Ch 379]