In primary open-angle glaucoma, which optic disc finding appears earliest in the disease progression?

Explanation

## Optic Disc Changes in POAG Progression ### Early Disc Changes **Key Point:** Vertical cup-to-disc ratio enlargement with characteristic superior and inferior notching of the neuroretinal rim is the earliest optic disc finding in POAG. ### Sequence of Optic Disc Cupping The characteristic pattern of optic nerve damage in POAG follows a predictable sequence: | Stage | Finding | Characteristics | |-------|---------|------------------| | **Early** | Vertical cup enlargement | Increased vertical C/D ratio; superior and inferior notching of rim | | **Moderate** | Progressive rim loss | Nasal rim involvement; temporal rim preserved longer | | **Advanced** | Complete cupping | Total loss of neuroretinal rim; complete pallor | ### Why Vertical Notching Occurs First 1. The superior and inferior poles of the optic disc are most vulnerable to pressure-induced damage 2. These regions have the thinnest neuroretinal rim initially 3. Axonal loss at poles precedes other areas 4. Vertical elongation of cup occurs before generalized enlargement **High-Yield:** The **"ISNT rule"** states that in healthy optics: Inferior rim > Superior rim > Nasal rim > Temporal rim. Violation of this rule (especially when Inferior < Superior) suggests glaucomatous damage. **Mnemonic:** **VISON** — **V**ertical cup enlargement → **I**nferior notching → **S**uperior notching → **O**ptic atrophy → **N**asal rim loss **Clinical Pearl:** Disc hemorrhages at the margin are often associated with early to moderate POAG and indicate active glaucomatous progression, though they are not the earliest finding. [cite:Khurana Comprehensive Ophthalmology Ch 8]