In optic neuritis, which pattern of visual field defect is most commonly observed?

Explanation

## Visual Field Defects in Optic Neuritis **Key Point:** Central scotoma is the most characteristic visual field defect in optic neuritis, reflecting inflammation of the optic nerve fibers in the papillomacular bundle. ### Pathophysiology of Central Scotoma - Optic neuritis typically affects the papillomacular bundle of the optic nerve - The papillomacular bundle carries fibers from the macula and central vision - Inflammation of these fibers results in a central scotoma (typically 5–10° in size) - The scotoma is usually relative rather than absolute - Patients often report blurred vision or dimming of colors (especially red) in the affected area ### Visual Field Defects in Optic Neuritis | Defect Type | Frequency | Characteristics | Cause | |-------------|-----------|-----------------|-------| | Central scotoma | Most common (60–70%) | Relative scotoma, 5–10°, affects central vision | Papillomacular bundle inflammation | | Paracentral scotoma | Common | Adjacent to fixation point | Variant of papillomacular involvement | | Arcuate defect | Less common | Follows nerve fiber layer distribution | Peripheral nerve fiber involvement | | Altitudinal defect | Rare | Superior or inferior field loss | Uncommon pattern in ON | | Peripheral constriction | Uncommon | Concentric field loss | Severe inflammation | **High-Yield:** Central scotoma with preserved peripheral vision is the hallmark finding in optic neuritis and helps differentiate it from other causes of vision loss (e.g., retinal or posterior segment pathology). **Clinical Pearl:** Patients with central scotoma in optic neuritis often describe a relative defect—they can still perceive light and color in the scotomatous area but with reduced brightness and desaturation of colors, especially red (red desaturation is a classic sign). **Mnemonic:** **PION** = Papillomacular bundle → Inflammation → Optic Neuritis → No peripheral loss (central scotoma preserves periphery) ### Why Central Scotoma is the Answer The papillomacular bundle, which carries fibers from the macula and central retina, is the most commonly affected region in optic neuritis. Inflammation of these fibers produces a central scotoma—the most frequent and characteristic visual field defect.