**Question:** Drug kept as a last resort in the management of primary open angle glaucoma is -

A. Timolol
B. Beta blockers
C. Prostaglandin analogues
D. Carbonic anhydrase inhibitors

**Core Concept:** In the treatment of primary open angle glaucoma, a selective beta-blocker like timolol is often used as a last resort due to its potential side effects and limited efficacy compared to newer medications. Primary open angle glaucoma is a chronic eye condition characterized by increased intraocular pressure (IOP) resulting from a blockage or reduced outflow of aqueous humor from the eye.

**Why the Correct Answer is Right:** Timolol, a beta blocker, is prescribed as a last resort due to its limited efficacy in lowering IOP and the potential side effects associated with its use. Beta-blockers, including timolol, work by blocking the action of catecholamines at beta receptors, reducing the production of aqueous humor and lowering IOP. However, their effectiveness in reducing IOP is less compared to newer drugs like prostaglandin analogues.

**Why Each Wrong Option is Incorrect:**

B. Beta-blockers (e.g., timolol) are not as effective as newer medications in lowering IOP, making them a later choice in treatment.
C. Prostaglandin analogues are a newer class of medications with higher efficacy in reducing IOP and are often used first-line or second-line therapy in glaucoma management.
D. Carbonic anhydrase inhibitors (e.g., brinzolamide) are a different class of drugs used in glaucoma management, acting on carbonic anhydrase enzymes within the ciliary body to reduce the production of aqueous humor. However, they are typically prescribed after prostaglandin analogues due to their lower efficacy and potential side effects.

**Clinical Pearl:**

In the management of primary open angle glaucoma, the choice of medications is based on the severity of the patient's condition and their response to prior treatments. Beta-blockers like timolol are typically used later in the treatment plan due to their limited efficacy and potential side effects. Timolol's use as a last resort ensures that patients receive more effective medications earlier in their management, reducing the risk of long-term visual damage caused by elevated intraocular pressure.