What is the mechanism of action of pilocarpine in acute closed-angle glaucoma?

AIIMS Rishikesh NO - 2019

Pharmacology

Easy

Appeared in: AIIMS Rishikesh NO - 2019

Explanation

Pilocarpine is a direct-acting cholinergic agonist, also known as a miotic agent.
It works by stimulating muscarinic receptors in the eye's iris sphincter muscle, causing the pupil to constrict (miosis).
In acute angle-closure glaucoma, the iris blocks the drainage pathway (trabecular meshwork).
Pupillary constriction physically pulls the iris away from the trabecular meshwork, opening the drainage angle.
This action increases the outflow (drainage) of aqueous humor, which in turn lowers the dangerously high intraocular pressure (IOP).

Option B: This is the opposite of pilocarpine's effect. Pilocarpine is a miotic, meaning it constricts the pupil.
Option C: Pilocarpine's primary mechanism is to improve the outflow (drainage) of aqueous humor, not to increase its absorption.
Option D: The entire purpose of administering pilocarpine in glaucoma is to decrease intraocular pressure (IOP), not increase it.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Mechanism of action of pilocarpine in acute closed-angle glaucoma as background academic context rather than a clinical decision trigger.
Acute angle-closure glaucoma is a medical emergency that can lead to rapid and irreversible vision loss if not treated promptly. Pilocarpine is a key medication in its initial management.
Nurses must monitor for both the therapeutic effect (decreased eye pain, reduced IOP) and side effects, which include blurred vision, brow ache, and potential systemic cholinergic effects like sweating or bradycardia.
Patient education is critical. The nurse should explain that the medication will cause the pupil to become smaller and may cause temporary dimness of vision, especially at night.

How to Approach the Question

First, identify the key terms in the question: 'pilocarpine' and 'acute closed-angle glaucoma'.
Recall the drug class of pilocarpine. It is a cholinergic agonist, which means it mimics the parasympathetic nervous system. A key action of the parasympathetic system on the eye is pupillary constriction (miosis).
Understand the pathophysiology of acute closed-angle glaucoma: the drainage angle for aqueous humor is physically blocked by the iris, causing a rapid rise in pressure.
Connect the drug's action to the disease. How would constricting the pupil affect a physically blocked angle? Constriction makes the iris tissue taut and pulls it away from the drainage meshwork.
Evaluate the options based on this logic. Constricting the pupil to increase outflow directly addresses the problem. Dilating the pupil would worsen it. Increasing absorption is not the mechanism, and increasing pressure is the opposite of the goal.

Concept Tested & Keywords

Concept Tested: Mechanism of action of pilocarpine in acute closed-angle glaucoma
Stem keywords: pilocarpine, mechanism of action, acute closed-angle glaucoma
Lead-in keywords: What is
Negative lead-in flag: false

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