## Methanol Poisoning: Ocular Toxicity **Key Point:** Methanol has a specific affinity for the optic nerve. Formic acid (the toxic metabolite) causes: - Demyelination of optic nerve fibers - Optic neuritis - Optic atrophy - **Permanent blindness** (often irreversible even with treatment) ## Pathophysiology **High-Yield:** The mechanism of optic nerve damage: 1. Formic acid accumulates in the retina and optic nerve 2. Inhibits cytochrome oxidase in mitochondria 3. Causes energy depletion in retinal ganglion cells 4. Leads to demyelination and axonal degeneration 5. Results in optic atrophy and vision loss ## Clinical Features of Methanol Poisoning | Stage | Timing | Features | | --- | --- | --- | | Early (0–12 hrs) | Immediate | Inebriation, headache, nausea, vomiting | | Latent (12–24 hrs) | Deceptive improvement | Apparent recovery (false reassurance) | | Toxic (24–72 hrs) | Metabolite accumulation | Acidosis, blindness, CNS depression | | Late (>72 hrs) | Complications | Optic atrophy, permanent sequelae | **Clinical Pearl:** The "latent phase" is dangerous because patients may appear to improve, delaying treatment. By the time ocular symptoms appear, optic nerve damage may be irreversible. **Mnemonic:** **FOAM** — Formic acid → Optic nerve → Atrophy → Methanol poisoning ## Why Blindness Occurs Formic acid preferentially damages: - Optic nerve head (demyelination) - Retinal ganglion cells (energy depletion) - Optic nerve axons (irreversible degeneration) Unlike other organs, the optic nerve has limited regenerative capacity, making vision loss often permanent.
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