What is the effect of cholinergic agents on pupil size?

Cholinergic agents, such as acetylcholine and drugs that mimic its action, primarily activate the muscarinic receptors in the eye. Activation of these receptors leads to the contraction of the sphincter muscle of the iris, resulting in the constriction of the pupil, a process known as miosis. This effect is particularly pronounced with medications used in ocular applications, such as pilocarpine, which is utilized in treating conditions like glaucoma by promoting drainage of intraocular fluid and thus lowering intraocular pressure.

In contrast, pupil dilation, or mydriasis, is typically achieved through the action of adrenergic agents that stimulate the dilator muscle of the iris. Therefore, the correct understanding of cholinergic agents is that their predominant effect is on pupil constriction, making the second option the accurate choice. Variable pupil size and no effect on pupil size do not accurately reflect the actions of cholinergic agents since they consistently induce constriction when these agents are active.