**Question:** Drug used in glaucoma is –

A. Timolol
B. Brimonidine
C. Dorzolamide
D. Phenylephrine

**Core Concept:** Glaucoma is a group of eye disorders characterized by elevation of intraocular pressure (IOP), leading to optic nerve damage and vision loss. IOP is regulated by the balance between production and absorption of aqueous humor, a clear fluid that fills the anterior chamber of the eye.

**Why the Correct Answer is Right:** The correct answer, A (Timolol), is a beta-blocker that inhibits the production of aqueous humor by blocking beta-adrenergic receptors in the ciliary body. This reduces the aqueous humor production, thus lowering intraocular pressure and protecting the optic nerve from damage.

**Why Each Wrong Option is Incorrect:**

B. Brimonidine (Option B) is a alpha-2 adrenergic agonist. Although alpha-2 agonists can lower IOP by reducing aqueous humor production, beta-blockers like Timolol are more commonly used due to their better efficacy and safety profile.

C. Dorzolamide (Option C) is a carbonic anhydrase inhibitor that reduces aqueous humor production, similar to Timolol. However, it is often combined with Timolol to enhance their synergistic effect in lowering IOP.

D. Phenylephrine (Option D) is a peripheral alpha-1 agonist, which raises IOP by constricting the pupil and reducing aqueous humor outflow. It is contraindicated in glaucoma treatment.

**Clinical Pearl:** In glaucoma management, combining a beta-blocker like Timolol with a carbonic anhydrase inhibitor like Dorzolamide provides a more potent and safe approach to lowering intraocular pressure and preserving visual function.

**Correct Answer:** D. Timolol (Timolol Maleate) is a selective beta-blocker that reduces aqueous humor production by blocking beta-adrenergic receptors in the ciliary body, ultimately lowering intraocular pressure and protecting the optic nerve.