Cholinomimetic drugs are useful for treating glaucoma because they can decrease the resistance to the movement of fluid (aqueous humor) out of the eye (Fig. 12.3), thereby reducing the intraocular pressure. It is useful to distinguish between open-angle glaucoma, a chronic condition in which the porosity of the trabecular mesh-work is insufficient to permit the movement of fluid into the canal of Schlemm, and angle-closure glaucoma, an emergency condition in which an abnormal position of the peripheral iris blocks the access of fluid to the tra-becular meshwork. Open-angle glaucoma can be effectively treated with cholinomimetics such as pilocarpine and carbachol, because contraction of the ciliary muscle stretches the trabecular network, increasing its porosity
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