**Core Concept**
Chloroquine is a 4-aminoquinoline antimalarial drug that can cause retinal pigmentation as a side effect, leading to visual disturbances and potentially irreversible vision loss. This is a well-documented adverse effect of long-term chloroquine therapy.

**Why the Correct Answer is Right**
Chloroquine is known to accumulate in the retinal pigment epithelium (RPE), causing photoreceptor damage and leading to retinal pigmentation. The exact mechanism involves the formation of toxic chloroquine metabolites, which bind to melanin in the RPE, resulting in oxidative stress and photoreceptor degeneration. This process can be exacerbated by factors such as age, dose, and duration of treatment.

**Why Each Wrong Option is Incorrect**
**Option A:** Quinine, another antimalarial drug, can cause visual disturbances, but it is not typically associated with retinal pigmentation.
**Option C:** Mefloquine, a related antimalarial, has a different side effect profile and is not known to cause retinal pigmentation.
**Option D:** Atovaquone, a newer antimalarial, has a more favorable side effect profile and is not associated with retinal pigmentation.

**Clinical Pearl / High-Yield Fact**
Chloroquine-induced retinal toxicity is often irreversible, emphasizing the importance of regular eye exams and monitoring for patients on long-term chloroquine therapy.

**✓ Correct Answer: B. Chloroquine**