A 58-year-old Indian man with newly diagnosed POAG (IOP 26 mmHg, cup-to-disc ratio 0.7) and mild myopia is compared with a 58-year-old man with ocular hypertension (IOP 28 mmHg, cup-to-disc ratio 0.3, normal visual fields). Which finding best discriminates true POAG from ocular hypertension?

## POAG vs. Ocular Hypertension: The Critical Discriminator ### Definition and Distinction **Key Point:** The cardinal difference between POAG and ocular hypertension (OHT) is the **presence of glaucomatous optic nerve damage and corresponding visual field loss in POAG**. Elevated IOP alone does not define glaucoma; structural and functional damage must be present. ### Diagnostic Criteria Comparison | Parameter | POAG | Ocular Hypertension | | --- | --- | --- | | **IOP** | Usually elevated (>21 mmHg) | Elevated (>21 mmHg) | | **Optic disc cupping** | Present (progressive) | Absent or minimal | | **Cup-to-disc ratio** | ≥0.7 (often asymmetric) | <0.5 (symmetric) | | **Visual field defect** | Present (arcuate, nasal step, altitudinal) | Normal | | **Gonioscopy** | Open angles | Open angles | | **Anterior chamber** | Normal depth | Normal depth | | **Diagnosis** | **Glaucoma** (requires treatment) | **Risk factor** (observation) | **High-Yield:** OHT is defined purely by IOP elevation WITHOUT optic nerve damage or visual field loss. Up to 25% of patients with OHT will develop POAG over 5–10 years; the rest remain stable. ### Clinical Pearl **Clinical Pearl:** In the scenario above, the first patient has a cup-to-disc ratio of 0.7 with elevated IOP — this suggests glaucomatous cupping. The second patient has a cup-to-disc ratio of 0.3 with normal visual fields despite higher IOP — this is OHT. The presence of optic nerve damage (not IOP level) defines glaucoma. ### Mnemonic **Mnemonic: POAG = "Damage Present"** - **P**ressure + **O**ptic nerve damage + **A**ltered visual field + **G**laucoma diagnosis - OHT = Pressure alone (no damage) ### Why IOP Alone Is Not Enough **Warning:** A common misconception is that IOP >21 mmHg = glaucoma. This is **false**. Many patients with IOP >21 mmHg never develop glaucoma (OHT). Conversely, some patients with "normal" IOP (<21 mmHg) develop glaucoma (normal-tension glaucoma). The diagnosis of glaucoma requires **evidence of optic nerve damage** (cupping, RNFL thinning) and/or **visual field defects**. **High-Yield:** The Early Manifest Glaucoma Trial (EMGT) and Ocular Hypertension Treatment Study (OHTS) established that glaucomatous damage (not IOP alone) defines the disease and determines treatment urgency. [cite:Parson's Diseases of the Eye 22e Ch 11]