**Core Concept**
Bull's eye retinopathy is a specific type of retinal toxicity characterized by a ring of retinal pigment epithelium atrophy surrounding a central area of retinal pigment epithelium hypertrophy, leading to visual field defects. This condition is often associated with long-term use of certain medications.

**Why the Correct Answer is Right**
Chloroquine, an antimalarial medication, is a well-documented cause of bull's eye retinopathy. The mechanism behind this toxicity involves the accumulation of chloroquine in the retinal pigment epithelium, leading to cellular damage and apoptosis. The resulting retinal damage can cause permanent visual field defects and vision loss. Chloroquine's ability to accumulate in the retina is due to its lipophilic nature, which allows it to easily cross cell membranes and reach toxic concentrations in the retina.

**Why Each Wrong Option is Incorrect**
**Option A:** Quinine, another antimalarial medication, can cause visual disturbances, but it is not typically associated with bull's eye retinopathy. Quinine toxicity is more likely to cause visual field defects and altered color perception without the characteristic bull's eye pattern.

**Option B:** Tobacco use is associated with a range of ocular disorders, including age-related macular degeneration, cataracts, and optic neuropathy. However, tobacco use is not directly linked to bull's eye retinopathy.

**Option C:** Chronic ethanol exposure can cause a range of ocular complications, including optic neuropathy and cataracts. However, ethanol toxicity is not typically associated with bull's eye retinopathy.

**Clinical Pearl / High-Yield Fact**
Bull's eye retinopathy is a classic example of a medication-induced ocular toxicity. It is essential for clinicians to recognize the potential for this condition in patients taking long-term chloroquine therapy and to monitor for early signs of retinal toxicity. Early detection and cessation of chloroquine therapy can help prevent permanent vision loss.

**✓ Correct Answer: D. Chloroquine**