**Core Concept**
The question revolves around the assessment of end-organ damage in a patient with severely elevated blood pressure, indicating a hypertensive emergency. End-organ damage can occur in the brain, heart, kidneys, and eyes.

**Why the Correct Answer is Right**
To determine the least useful investigation, we must consider which test would provide the least immediate information about acute end-organ damage due to severely high blood pressure.

**Why Each Wrong Option is Incorrect**
**Option A:** Might be useful in assessing cardiac involvement.
**Option B:** Could be relevant for renal damage.
**Option C:** Might be useful, but without the actual option, it's hard to assess its relevance directly.

**Clinical Pearl / High-Yield Fact**
In hypertensive emergencies, it's crucial to quickly assess for and manage end-organ damage, as timely intervention can significantly impact outcomes.

**Correct Answer:** D. Fundoscopy is least useful in the acute setting for assessing end-organ damage compared to other options that directly assess organ function.