A 55-year-old man with newly diagnosed open-angle glaucoma is started on timolol eye drops. The mechanism by which timolol reduces intraocular pressure is:
- A Relaxation of ciliary muscle via beta-2 blockade
- B Reduction of aqueous humor production by blockade of beta-2 receptors in the ciliary epithelium ✓
- C Increased uveoscleral outflow via alpha-1 blockade
- D Pupillary constriction increasing trabecular outflow
Correct answer: B. Reduction of aqueous humor production by blockade of beta-2 receptors in the ciliary epithelium
Explanation
Timolol is a non-selective beta-blocker used topically in glaucoma. It reduces aqueous humor production by blocking beta-2 adrenergic receptors in the ciliary epithelium. It does not affect outflow facility or pupil size. The reduction in aqueous formation lowers intraocular pressure. Pilocarpine, not timolol, causes pupillary constriction. Latanoprost increases uveoscleral outflow. Beta-1 selective blockers like betaxolol are also used but timolol remains the prototype topical beta-blocker for glaucoma.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.