Intraocular pressure, alpha agonists

In the eye, the radial pupillary dilator muscle of the iris contains oo receptors activation by drugs such as phenylephrine causes mydriasis (see Figure 6-9). Alpha stimulants also have important effects on intraocular pressure. Alpha agonists increase the outflow of aqueous humor from the eye and can be used clinically to reduce intraocular pressure. In contrast, agonists have little effect, but antagonists decrease the production of aqueous humor. These effects are important in the treatment of glaucoma (see Chapter 10), a leading cause of blindness. 

Mechanism of Action An ocular alpha-adrenergic agent that is a relatively selective alphaj receptor agonist. Therapeutic Effect Reduces intraocular pressure. 

Eye The smooth muscle of the pupillary dilator responds to topical phenylephrine and similar alpha agonists with mydriasis. Accommodation is not significantly affected. Outflow of aqueous humor may be facilitated by nonselective alpha agonists, with a subsequent reduction of intraocular pressure. Alpha2-selective agonists also reduce intraocular pressure, apparently by reducing synthesis of aqueous humor. 

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