**Core Concept**
Mydriatics are medications that cause pupil dilation by relaxing the circular muscles of the iris (sphincter pupillae) or constricting the radial muscles (dilator pupillae). This results in an increase in pupil size, which can be useful in ophthalmic examinations or to relieve photophobia.

**Why the Correct Answer is Right**
Tropicamide, phenylephrine, and cyclopentolate are examples of mydriatics. Tropicamide works by competitively blocking muscarinic acetylcholine receptors in the iris sphincter pupillae, leading to pupil dilation. Phenylephrine is an alpha-adrenergic agonist that causes vasoconstriction and subsequent mydriasis by stimulating the radial muscles. Cyclopentolate is a non-selective muscarinic antagonist that blocks the parasympathetic input to the iris sphincter pupillae, resulting in pupil dilation.

**Why Each Wrong Option is Incorrect**
**Option A:** Atropine is a mydriatic, not an exception. It is a non-selective muscarinic antagonist that blocks parasympathetic input to the iris sphincter pupillae, resulting in pupil dilation.
**Option B:** Cyclobenzaprine is not a mydriatic. It is a muscle relaxant used primarily to treat muscle spasms and has no effect on pupil size.
**Option C:** Homatropine is a mydriatic. It is an anticholinergic agent that blocks muscarinic receptors in the iris sphincter pupillae, leading to pupil dilation.
**Option D:** Pilocarpine is a miotic, not a mydriatic. It is a muscarinic agonist that stimulates the parasympathetic input to the iris sphincter pupillae, resulting in pupil constriction.

**Clinical Pearl / High-Yield Fact**
When using mydriatics, note that they can also cause cycloplegia (paralysis of accommodation), which can be useful in ophthalmic examinations but may also cause blurred vision.

**Correct Answer:** B. Cyclobenzaprine is not a mydriatic.