The α2 agonist used in glaucoma is:
**Core Concept**
The α2 agonist used in glaucoma works by decreasing the production of aqueous humor, thereby reducing intraocular pressure. This is achieved through the activation of α2 adrenergic receptors in the ciliary body, which leads to a decrease in the release of norepinephrine and a subsequent decrease in aqueous humor production.
**Why the Correct Answer is Right**
Brimonidine is a selective α2 adrenergic receptor agonist that is used in the treatment of glaucoma. When brimonidine binds to α2 adrenergic receptors in the ciliary body, it activates a G-protein coupled receptor pathway that ultimately leads to a decrease in the release of norepinephrine. This decrease in norepinephrine release results in a decrease in the production of aqueous humor, which in turn reduces intraocular pressure. The α2 adrenergic receptors involved in this process are primarily located on the ciliary epithelium, where they play a key role in regulating aqueous humor production.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because α1 agonists, such as phenylephrine, increase intraocular pressure by constricting the pupils and increasing the production of aqueous humor.
**Option B:** This option is incorrect because β blockers, such as timolol, decrease intraocular pressure by reducing the production of aqueous humor, but they do not act through α2 adrenergic receptors.
**Option D:** This option is incorrect because prostaglandin analogs, such as latanoprost, decrease intraocular pressure by increasing the outflow of aqueous humor, but they do not act through α2 adrenergic receptors.
**Clinical Pearl / High-Yield Fact**
Brimonidine is a selective α2 adrenergic receptor agonist that is used in the treatment of glaucoma. It is also a potent vasoconstrictor, which can cause systemic side effects such as hypotension and bradycardia.
**Correct Answer:** C. Brimonidine