## Core Concept
The question revolves around the appropriate management of a patient with a metallic foreign body in the eye. The key principle here involves understanding the potential risks associated with certain diagnostic investigations in the presence of metallic foreign bodies, particularly in the context of magnetic resonance imaging (MRI).

## Why the Correct Answer is Right
The correct answer, MRI, should not be done in a patient with a metallic foreign body in the eye because MRI uses powerful magnetic fields. If the metallic foreign body is ferromagnetic, it can move or heat up due to the magnetic field, potentially causing further injury, including hemorrhage or retinal damage.

## Why Each Wrong Option is Incorrect
- **Option A:** Not specified, but assuming it's an imaging technique like CT scan, it's not incorrect because CT scans can be used to locate metallic foreign bodies without the risks associated with MRI.
- **Option B:** Similarly, not specified, but if it's another form of imaging or investigation, the reasoning would depend on its safety profile in this context.
- **Option D:** Without specifics, if this option is another diagnostic tool, its appropriateness would depend on whether it poses a risk to the patient with a metallic foreign body.

## Clinical Pearl / High-Yield Fact
A crucial point to remember is that in cases of suspected metallic foreign bodies, especially in the eye, **CT scan** is often the preferred initial imaging modality because it can accurately locate the foreign body without the risks associated with MRI. Additionally, the presence of a metallic foreign body is a critical consideration in the management of ocular trauma.

## Correct Answer: B. MRI.