## **Core Concept**
Mydriatics are medications used to dilate the pupils, often for ophthalmic examinations or procedures. They work by either stimulating the dilator pupillae muscle or inhibiting the sphincter pupillae muscle. Common mydriatics include anticholinergics and sympathomimetics.

## **Why the Correct Answer is Right**
The correct answer, , is not a mydriatic because it is actually a cholinergic agonist, which would cause pupil constriction (miosis), not dilation (mydriasis). Cholinergic agonists stimulate the muscarinic receptors in the eye, leading to contraction of the sphincter pupillae muscle and thus pupil constriction.

## **Why Each Wrong Option is Incorrect**
* **Option A:** is a mydriatic because it is an anticholinergic agent that blocks muscarinic receptors, preventing the sphincter pupillae muscle from contracting and thus causing pupil dilation.
* **Option B:** is a mydriatic as it acts as a sympathomimetic agent, stimulating the alpha-adrenergic receptors in the radial muscle of the iris, leading to pupil dilation.
* **Option D:** is also a mydriatic, working through anticholinergic effects similar to .

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that physostigmine, an acetylcholinesterase inhibitor (like ), can be used to treat severe anticholinergic toxicity, including mydriasis caused by anticholinergic mydriatics. This can be a helpful clue in distinguishing between different types of agents.

## **Correct Answer:** . Pilocarpine