**Core Concept**
Pilocarpine is a muscarinic receptor agonist that plays a crucial role in managing glaucoma by influencing the intraocular pressure. The primary mechanism of action in this context involves the regulation of aqueous humor dynamics, specifically the outflow.

**Why the Correct Answer is Right**
Pilocarpine stimulates the muscarinic receptors in the ciliary epithelium, leading to the contraction of the ciliary muscle. This contraction results in the opening of the trabecular meshwork, thereby increasing the outflow of aqueous humor. As a result, the intraocular pressure decreases. The increased outflow of aqueous humor is the primary mechanism by which pilocarpine reduces intraocular pressure in individuals with closed-angle glaucoma.

**Why Each Wrong Option is Incorrect**
**Option A:** Reducing aqueous humour secretion is a mechanism associated with beta-blockers, not muscarinic agonists like pilocarpine. Pilocarpine does not decrease the production of aqueous humor.
**Option B:** Pilocarpine does not directly contract the iris sphincter muscle; this is the primary action of miotics like carbachol.
**Option D:** Relaxing the ciliary muscle would actually decrease the outflow of aqueous humor, leading to increased intraocular pressure.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that pilocarpine is not used as a first-line treatment for glaucoma due to its potential side effects, such as miosis and accommodative spasm. Therefore, it is crucial to carefully weigh the benefits and risks before prescribing this medication.

**✓ Correct Answer: C. Increasing aqueous humour outflow**