In ophthalmology, topical adrenergic agonists primarily target which receptor subtypes?

• A. A1 and A2 receptors
• B. B1 and B2 receptors
• C. Dopamine receptors
• D. Alpha1 receptor only

Answer: (A)

Topical adrenergic agonists in the eye mainly engage alpha-adrenergic receptors. The two subtypes involved are alpha-1 and alpha-2. Activation of alpha-2 receptors on the ciliary body reduces aqueous humor production, which lowers intraocular pressure; drugs like brimonidine and apraclonidine are examples of this alpha-2–selective action. Alpha-1 receptor activation affects the iris dilator muscle, producing pupil dilation (phenylephrine is a clinical example), but this isn’t the primary mechanism for lowering IOP. Beta receptors play a lesser or indirect role in this topical context, and dopamine receptors are not involved. So the receptor subtypes targeted are alpha-1 and alpha-2 receptors.