A 62-year-old man presents with progressive visual field loss. Perimetry reveals a superior arcuate defect in the right eye. What is the most common site of lesion causing this pattern of visual field defect?

Explanation

## Arcuate Visual Field Defects: Anatomy & Pathology ### Definition & Pattern Arcuate (or Bjerrum) defects follow the course of retinal nerve fiber bundles (RNFB) in the retina. They originate at the optic disc and curve around the macula, respecting the horizontal meridian. ### Most Common Site: Retinal Nerve Fiber Layer (RNFL) **Key Point:** Arcuate defects are hallmark of **glaucomatous optic neuropathy** and occur due to selective loss of nerve fibers in the superior or inferior temporal quadrants of the RNFL. ### Mechanism of Arcuate Defects 1. Nerve fiber bundles in the RNFL are arranged in a specific pattern 2. Superior temporal and inferior temporal bundles are most vulnerable to elevated intraocular pressure 3. Damage follows the natural course of these bundles → arcuate pattern 4. Defect respects the horizontal meridian (does NOT cross it) ### Why RNFL (Superior Temporal Quadrant) is Most Common | Feature | Superior Arcuate | Inferior Arcuate | |---------|------------------|------------------| | **Frequency** | ~70% of glaucomatous VFD | ~30% of glaucomatous VFD | | **RNFL location** | Superior temporal quadrant | Inferior temporal quadrant | | **Mechanism** | IOP-induced ischemia of superior temporal bundles | IOP-induced ischemia of inferior temporal bundles | | **Associated optic disc finding** | Superior temporal notching | Inferior temporal notching | **High-Yield:** Superior arcuate defects are more common than inferior ones in primary open-angle glaucoma (POAG), making the superior temporal RNFL the most frequent site of pathology. ### Clinical Pearl Arcuate defects are **monocular** (confined to one eye) and respect the **horizontal meridian**—these features distinguish them from chiasmal or post-chiasmal lesions, which typically cross the meridian or are bilateral. ### Differential: Why Other Sites Are Wrong - **Optic disc involvement**: While glaucoma causes optic disc cupping, the arcuate pattern arises from RNFL loss, not primary disc pathology - **Optic chiasm**: Chiasmal lesions produce **bitemporal hemianopia** (crossing both meridians), not monocular arcuate defects - **Optic tract**: Tract lesions cause **homonymous hemianopia** (affecting both eyes symmetrically), not monocular defects [cite:Duke Ophthalmology Ch 8 - Visual Fields]