## Pathophysiology and Risk Factors of POAG ### Correct Mechanism: Trabecular Meshwork Dysfunction **Key Point:** The hallmark pathophysiology of POAG is increased resistance to aqueous humor outflow, primarily at the level of the trabecular meshwork and Schlemm's canal. This is NOT due to angle closure but to microscopic changes in trabecular architecture and function. ### Why Elevated Episcleral Venous Pressure is NOT a Primary Mechanism **High-Yield:** Elevated episcleral venous pressure is a recognized cause of secondary glaucoma (e.g., cavernous sinus thrombosis, superior vena cava syndrome, Sturge-Weber syndrome). It is NOT an established primary mechanism in POAG. In POAG, the problem lies within the eye itself—at the trabecular meshwork—not in the episcleral venous drainage system. ### Established Risk Factors in POAG | Risk Factor | Evidence | Comment | |---|---|---| | Age >40 years | Strong | Incidence increases with age; rare before age 40 | | Family history | Strong | 5–10× increased risk with positive family history | | Elevated IOP | Strongest | Modifiable risk factor; main target of therapy | | Reduced ocular perfusion pressure | Moderate | Due to systemic hypertension, nocturnal hypotension, or vasculopathy | | African descent | Strong | Higher prevalence and earlier onset | | Myopia | Moderate | Increased risk compared to emmetropia | | Trabecular meshwork dysfunction | Fundamental | Increased resistance to aqueous outflow | | Vascular insufficiency | Moderate | Impaired optic nerve head perfusion | **Clinical Pearl:** Ocular perfusion pressure (OPP) = Mean arterial pressure − IOP. Patients with systemic hypertension treated aggressively may paradoxically worsen glaucoma if nocturnal blood pressure drops excessively, reducing OPP. ### Mechanism Diagram ```mermaid flowchart TD A[Aqueous Humor Production]:::action --> B[Normal: 2.5 µL/min] C[Aqueous Humor Outflow]:::action --> D{Resistance at TM?} D -->|Normal| E[IOP 10-21 mmHg]:::outcome D -->|Increased| F[IOP >21 mmHg]:::urgent F --> G[Optic nerve head ischemia] G --> H[Axonal loss & cupping]:::outcome I[Episcleral venous pressure]:::action -.->|Secondary glaucoma only| F ``` **Warning:** Do not confuse POAG with secondary glaucomas caused by elevated episcleral venous pressure. POAG is a primary disorder of aqueous humor dynamics within the eye.
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.