**Question:** Which of the antipsychotic medications causes cataract?

**Core Concept:** Antipsychotic medications are a class of drugs used to treat mental health disorders, particularly schizophrenia and bipolar disorder. They primarily act on dopamine and serotonin neurotransmitter systems in the brain. Cataracts are a condition that affects the lens of the eye, causing vision impairment.

**Why the Correct Answer is Right:** The correct answer, D, refers to the antipsychotic medication clozapine (Clozaril). Clozapine is a second-generation antipsychotic drug that primarily acts on dopamine D2 receptors in the brain. However, it also has a unique property of binding to the alpha-4 beta-2 nicotinic acetylcholine receptor, which is not present in the dopamine D2 receptor pathway. This binding leads to the formation of a toxic protein complex, which causes the development of cataracts in some patients.

**Why Each Wrong Option is Incorrect:**

A. Haloperidol (Haldol): This is another second-generation antipsychotic drug, but its primary action is on dopamine D2 and D3 receptors, not causing cataract formation.

B. Olanzapine (Zyprexa): Similar to haloperidol, olanzapine primarily targets dopamine D2 receptors and does not cause cataract formation.

C. Quetiapine (Seroquel): Quetiapine acts primarily on serotonin receptors (5-HT2A and 5-HT2C) and dopamine D2 receptors, not causing cataract formation.

**Clinical Pearl:** Cataracts caused by antipsychotic medications are known as "drug-induced cataracts" or "neuroleptic-induced cataracts." This is a known side effect of clozapine, making it the correct answer among the provided options. Regular eye check-ups are essential for patients taking clozapine to monitor for this side effect, which can be managed through discontinuation of the drug or switching to another antipsychotic medication.