## Anticholinergic Drugs and Narrow-Angle Glaucoma **Key Point:** Anticholinergic drugs are absolutely contraindicated in narrow-angle glaucoma because they cause mydriasis (pupil dilation), which narrows the drainage angle and increases intraocular pressure (IOP). ### Mechanism of IOP Elevation in Narrow-Angle Glaucoma 1. **Normal pupil position:** Parasympathetic tone keeps the pupil constricted (miosis). 2. **Anticholinergic blockade:** Atropine and other anticholinergics block parasympathetic innervation of the iris sphincter muscle. 3. **Mydriasis occurs:** The unopposed sympathetic tone causes pupil dilation. 4. **Angle narrowing:** In predisposed eyes (narrow drainage angle), mydriasis pushes the iris forward, further narrowing the angle. 5. **Aqueous humor drainage impaired:** The trabecular meshwork is compressed, reducing outflow. 6. **IOP rises:** Elevated IOP can precipitate acute angle-closure glaucoma. **Warning:** Even topical anticholinergics (cyclopentolate, tropicamide) used for refraction can precipitate acute angle-closure in susceptible patients. ### Contrast: Open-Angle Glaucoma **Clinical Pearl:** Anticholinergics are relatively safer in open-angle glaucoma because the drainage angle is wide and resistant to iris-induced narrowing. However, they are still generally avoided as a precaution. **High-Yield:** The mnemonic for drugs contraindicated in narrow-angle glaucoma includes anticholinergics, sympathomimetics (phenylephrine), and tricyclic antidepressants—all cause mydriasis. **Mnemonic:** **SAADC** = **S**ympathomimetics, **A**nticholinergics, **A**ntidepressants, **D**econgestants, **C**old remedies — all contraindicated in narrow-angle glaucoma.
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