**Core Concept**
Mydriatics are drugs that cause pupil dilation, while cycloplegics are drugs that cause paralysis of accommodation, resulting in loss of near vision. The question requires knowledge of the pharmacological effects of different mydriatic agents.

**Why the Correct Answer is Right**
Tropicamide is a non-anticholinergic mydriatic agent that works by stimulating the muscarinic receptors in the iris sphincter muscle, causing pupil dilation. However, it does not have any cycloplegic effect because it does not affect the ciliary muscles involved in accommodation. This is in contrast to anticholinergic mydriatics like atropine or cyclopentolate, which can cause both mydriasis and cycloplegia.

**Why Each Wrong Option is Incorrect**
* **Option A:** Atropine is an anticholinergic mydriatic agent that causes both pupil dilation and paralysis of accommodation, making it a cycloplegic agent as well.
* **Option B:** Cyclopentolate is an anticholinergic mydriatic agent that causes both pupil dilation and paralysis of accommodation, making it a cycloplegic agent as well.
* **Option D:** Homatropine is another anticholinergic mydriatic agent that causes both pupil dilation and paralysis of accommodation, making it a cycloplegic agent as well.

**Clinical Pearl / High-Yield Fact**
When choosing a mydriatic agent, it's essential to consider whether cycloplegia is desired or not. Tropicamide is a good choice for diagnostic purposes where cycloplegia is not required.

**Correct Answer: A. Tropicamide**