## Core Concept
Heterochromia iridis refers to the difference in color between the irises of an individual's eyes or between sections of the same iris. This condition can be caused by various factors, including genetics, injury, or certain medications. In the context of topical drugs, heterochromia iridis is notably associated with prostaglandin analogs used in the treatment of glaucoma.

## Why the Correct Answer is Right
Prostaglandin analogs, such as **latanoprost**, are used topically in the eye to reduce intraocular pressure in patients with glaucoma. One of the known side effects of these drugs is the potential to cause heterochromia iridis. This occurs because prostaglandin analogs can increase the melanin content within the iris, leading to a change in iris color. This effect is more noticeable in patients with mixed-color irises.

## Why Each Wrong Option is Incorrect
- **Option A:** While beta-blockers are used in the treatment of glaucoma, they are not commonly associated with heterochromia iridis. Their side effects more commonly include local irritation, bronchospasm, and bradycardia.
- **Option B:** Alpha agonists can be used in glaucoma treatment and have side effects like allergic conjunctivitis and dry mouth, but they are not typically associated with heterochromia iridis.
- **Option D:** Carbonic anhydrase inhibitors can be used topically for glaucoma and have side effects like local irritation and corneal edema, but they are not commonly linked with heterochromia iridis.

## Clinical Pearl / High-Yield Fact
A key point to remember is that prostaglandin analogs, such as **latanoprost**, **travoprost**, and **bimatoprost**, are not only effective in lowering intraocular pressure but also carry the risk of causing heterochromia iridis, especially in patients with heterochromatic irises. This side effect is irreversible and can be a significant consideration in the management of glaucoma.

## Correct Answer: C. Latanoprost