**Core Concept**
Herpes zoster ophthalmicus (HZO) is a reactivation of the varicella-zoster virus in the trigeminal nerve ganglion, affecting the ophthalmic division (V1). The **trigeminal nerve** has three divisions: ophthalmic (V1), maxillary (V2), and mandibular (V3).

**Why the Correct Answer is Right**
The correct answer is related to the anatomy of the **trigeminal nerve** and its involvement in HZO. The **ophthalmic division (V1)** is the most commonly affected, followed by the **maxillary division (V2)**. The least commonly involved is typically the **mandibular division (V3)**, due to its lesser involvement in the facial area affected by HZO.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the ophthalmic division is the most commonly involved.
**Option B:** Incorrect as the maxillary division can be involved, though less commonly than V1.
**Option C:** Incorrect as it is not the correct answer choice provided for the question.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that HZO can lead to serious complications, including **permanent vision loss** if not promptly treated.

**Correct Answer:** D. Mandibular division (V3)