**Core Concept**
Olopatadine is a topical antihistamine and mast cell stabilizer used in the treatment of allergic conjunctivitis. It works by inhibiting the release of histamine from mast cells and also has antihistaminic properties, providing relief from symptoms of allergic conjunctivitis such as itching, redness, and tearing.

**Why the Correct Answer is Right**
Olopatadine is a dual-action antihistamine and mast cell stabilizer. It binds to the H1 histamine receptor, thereby blocking the action of histamine and providing relief from itching, redness, and tearing. Additionally, it inhibits the release of histamine from mast cells, further reducing the symptoms of allergic conjunctivitis. Olopatadine's mechanism of action is mediated through its interaction with the H1 receptor and its ability to inhibit the release of histamine from mast cells.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as Olopatadine is not a selective COX-2 inhibitor, which is a class of nonsteroidal anti-inflammatory drugs (NSAIDs) used primarily for their anti-inflammatory and analgesic properties.
**Option B:** This option is incorrect as Olopatadine is not a beta-blocker, which is a class of medications used to treat hypertension, glaucoma, and other conditions by reducing heart rate and cardiac output.
**Option C:** This option is incorrect as Olopatadine is not an anticholinergic agent, which is a class of medications used to treat conditions such as Parkinson's disease, myasthenia gravis, and gastrointestinal disorders by blocking the action of acetylcholine.

**Clinical Pearl / High-Yield Fact**
Olopatadine is available in both ophthalmic and nasal spray formulations, providing relief from symptoms of allergic conjunctivitis and rhinitis. It is essential to note that Olopatadine should be used with caution in patients with glaucoma, as it may increase intraocular pressure.

**Correct Answer:** D. Olopatadine is a topical antihistamine and mast cell stabilizer used in the treatment of allergic conjunctivitis.