A 68-year-old woman with diabetes and hypertension undergoes automated perimetry showing a superior arcuate scotoma in the right eye. Which of the following is NOT consistent with this finding?

## Arcuate Scotoma: Definition & Pathophysiology **Key Point:** An **arcuate scotoma** is a monocular visual field defect that follows the course of retinal nerve fiber bundles (RNFL), which arch around the macula in a characteristic pattern. It respects the **horizontal meridian** and typically does not cross the vertical meridian. ## Recognized Causes of Arcuate Scotomas | Cause | Mechanism | Characteristics | |-------|-----------|------------------| | Glaucomatous optic neuropathy | Progressive RNFL loss from elevated IOP | Superior or inferior arcuate; bilateral; progressive | | Branch retinal artery occlusion (BRAO) | Ischemia to retinal territory | Arcuate or sectoral; follows vascular distribution | | Anterior ischemic optic neuropathy (AION) | Ischemia to optic nerve head | Altitudinal or arcuate; sudden onset | | Retinal migraine | Transient retinal ischemia | Arcuate; transient; monocular | **High-Yield:** Arcuate scotomas = **monocular**, **nerve fiber layer distribution**, **respects horizontal meridian** = **anterior segment pathology** (retina or optic nerve head). ## Why Posterior Cerebral Artery Occlusion Does NOT Cause Arcuate Scotomas **Clinical Pearl:** Posterior cerebral artery (PCA) occlusion causes infarction of the **occipital lobe**, leading to a **homonymous visual field defect** (same defect in both eyes). This is a **retrochiasmal** lesion and produces a **binocular, congruent** field loss that **respects the vertical meridian**, not the horizontal meridian. It cannot produce a monocular arcuate scotoma. **Mnemonic:** **RNFL Arcuate** = **monocular**, **respects horizontal**; **Occipital PCA** = **binocular**, **respects vertical**. ## Anatomical Basis: Monocular vs. Binocular VF Defects ```mermaid flowchart TD A["Visual Field Defect"]:::outcome --> B{"Monocular or\nBinocular?"}:::decision B -->|Monocular| C["Lesion anterior\nto optic chiasm"]:::outcome C --> D{"Pattern?"}:::decision D -->|Arcuate/Sectoral| E["Retina or optic\nnerve head"]:::outcome E --> F["Glaucoma, BRAO,\nAION, migraine"]:::action D -->|Altitudinal| G["Optic nerve head\nischemia"]:::outcome B -->|Binocular| H["Lesion at or\nbehind chiasm"]:::outcome H --> I{"Meridian\nrespected?"}:::decision I -->|Vertical| J["Homonymous\nHemianopia"]:::outcome J --> K["Optic tract, LGN,\nor occipital lobe"]:::outcome K --> L["PCA/MCA occlusion,\nstroke"]:::action ``` **Warning:** Do not confuse **arcuate scotoma** (monocular, RNFL distribution, anterior pathology) with **homonymous hemianopia** (binocular, vertical meridian, retrochiasmal pathology). PCA occlusion causes the latter, not the former. ## Differential Diagnosis Summary **Arcuate scotomas are monocular and anterior to the chiasm.** PCA occlusion affects the occipital lobe, which is posterior to the chiasm, and produces binocular (homonymous) field defects, not monocular arcuate scotomas. [cite:Harrison 21e Ch 29; Kanski's Clinical Ophthalmology]