The Pharmacology Case File 2

A 61 Year-old man is noted to have increased intraocular pressure on a routine eye examination. The visual acuity is normal in both eyes. The dilated eye examination reveals no evidence of optic nerve damage. Visual field testing shows mild loss of peripheral vision. He is diagnosed with primary open-angle glaucoma and is started on pilocarpine opthalmic drop. 

1. What is the action of pilocarpine on the muscles of the iris and cilia? 

2. What receptor mediates this Action?

Answers is :
1. Constriction of the muscles
2. Muscarinic cholinoreceptor

Clinical Correlation: 
Open-angle glaucoma is a disease caused by obstruction of the outflow of aqueous humor into the canal of Schlemm, causing an increase in intraocular pressure. The use of a direct acting muscarinic agonist, such as Pilocarpine, cause contraction of the muscles of the cilia and iris. Because these are circular muscles, the pupil is constricted, which helps to relieve the outflow obstruction and lower the intraocular pressure. Although not common with the use of topical opthalmic drops, bronchospasm and pulmonary edema has been noted with the use of pilocarpine  drops. More commonly, blurred vision and myopia (near-sightedness) occur as a result of the impairment of accommodation caused by the contraction of the iris and ciliary muscles

Effects of Cholinoreceptor activation: