A 68-year-old woman with diabetes and hyperlipidemia undergoes automated perimetry for routine screening. The test shows a superior arcuate scotoma in the right eye. All of the following are recognized causes of arcuate scotomas EXCEPT:

Explanation

## Arcuate Scotomas: Pathophysiology and Causes **Key Point:** An arcuate scotoma is a nerve fiber bundle defect (NFBD) that follows the course of retinal nerve fiber bundles as they arch around the macula and converge toward the optic disc. It is characteristic of lesions affecting the optic nerve head, anterior optic nerve, or retinal structures that follow nerve fiber bundle anatomy. ## Causes of Arcuate Scotomas | Cause | Mechanism | Arcuate Pattern? | Notes | | --- | --- | --- | --- | | Glaucoma | Optic nerve head cupping / RNFL loss | ✓ Yes | Most common cause; classic Bjerrum scotoma | | AION | Ischemia of optic disc | ✓ Yes | Altitudinal or arcuate defect; follows RNFL distribution | | BRAO | Retinal artery occlusion along arcuate RNFL | ✓ Yes | Occlusion of superior/inferior branch follows arcuate RNFL territory | | Retrobulbar Optic Neuritis | Demyelination posterior to globe | ✗ Typically NO | Classically produces a **central or centrocecal scotoma**, not an arcuate defect | **High-Yield:** Retrobulbar optic neuritis (as seen in multiple sclerosis) characteristically causes a **central scotoma** or **centrocecal scotoma** because the papillomacular bundle (which subserves central vision) is preferentially affected. Arcuate scotomas are NOT the typical presentation of retrobulbar optic neuritis. ## Why Branch Retinal Artery Occlusion CAN Cause Arcuate Scotomas **Clinical Pearl:** A BRAO affecting the superior or inferior branch of the central retinal artery occludes blood supply to a sector of retina that corresponds to the arcuate nerve fiber bundle territory. Because the superior and inferior retinal arteries follow the same arcuate distribution as the RNFL, the resulting visual field defect is often **arcuate or altitudinal** in shape — not merely a random wedge. This is well-recognized in clinical practice and standard ophthalmology texts. ## Why Retrobulbar Optic Neuritis is the EXCEPTION **Clinical Pearl:** In retrobulbar optic neuritis, the lesion is **posterior to the optic disc** and preferentially involves the papillomacular bundle. The classic visual field defect is a **central scotoma** (loss of central vision with preserved peripheral vision). Arcuate scotomas are not a recognized pattern for retrobulbar optic neuritis. The fundus appears normal ("the patient sees nothing and the doctor sees nothing"). **Mnemonic:** **Central = Retrobulbar ON** (papillomacular bundle affected) vs. **Arcuate = Optic disc / RNFL pathology** (Glaucoma, AION, BRAO). [cite: Khurana's Comprehensive Ophthalmology 6e Ch 12; Walsh & Hoyt's Clinical Neuro-Ophthalmology; American Academy of Ophthalmology BCSC Section 5]