**Question:** The first line of treatment of open angle glaucoma is -

A. Timolol
B. Latanoprost
C. Brimonidine
D. Pilocarpine

**Core Concept:** Open angle glaucoma is a type of glaucoma where the angle between cornea and iris remains open, leading to elevated intraocular pressure (IOP) and optic nerve damage. The primary goal of treatment is to reduce IOP to prevent further vision loss.

**Why the Correct Answer is Right:** The correct answer, D. Pilocarpine, belongs to a class of drugs called miotics, which are used to lower IOP by increasing outflow of aqueous humor through the conventional pathway. Pilocarpine stimulates the parasympathetic muscarinic receptors in the ciliary body, leading to increased frequency of ciliary body rotation and increased outflow of aqueous humor through the conventional pathway.

**Why Each Wrong Option is Incorrect:**

A. Timolol (beta-blocker) and B. Latanoprost (prostaglandin analogue) are both beta-blockers and prostaglandin analogues, respectively. These drug classes are not first-line treatment options for open angle glaucoma as they typically have weaker efficacy in lowering IOP compared to miotics.

C. Brimonidine is an alpha-agonist, which primarily affects the conventional pathway, but has a weaker effect on the uveoscleral outflow pathway compared to miotics.

**Clinical Pearl:** In open angle glaucoma, the primary treatment goal is to lower IOP promptly and effectively. Pilocarpine is a first-line choice due to its strong effect on conventional outflow pathway compared to other options. Beta-blockers and prostaglandin analogues might be considered as second-line options if the IOP remains elevated despite miotic therapy. Alpha-agonists like Brimonidine are typically used in combination with miotics or as a second-line agent when the IOP remains elevated despite first-line treatment.