**Core Concept**
The management of a metallic foreign body in the eye involves a thorough evaluation to prevent potential complications, such as siderosis (iron toxicity) or chalcosis (copper toxicity). This requires a careful examination and selection of diagnostic tests.

**Why the Correct Answer is Right**
In patients with a metallic foreign body in the eye, the main concern is the potential toxicity of the metal. A thorough slit-lamp examination is essential to identify the location and type of foreign body. The correct approach involves imaging studies, such as X-rays, to confirm the presence and location of the foreign body, and possibly CT or MRI scans for better visualization, especially if the foreign body is not visible on X-ray. However, certain investigations may not be necessary in this scenario.

**Why Each Wrong Option is Incorrect**
**Option A:** Slit-lamp examination is a crucial step in evaluating a metallic foreign body in the eye. It helps to identify the location and type of foreign body, and assess the integrity of the anterior segment.

**Option B:** X-rays are a necessary investigation to confirm the presence and location of the metallic foreign body.

**Option C:** CT scans may be used to better visualize the foreign body, especially if it is not visible on X-ray.

**Option D:** This option is not done because a routine ultrasound examination is not typically necessary for a metallic foreign body in the eye. Ultrasound can be useful in evaluating the posterior segment, but it is not the primary investigation for a metallic foreign body.

**Clinical Pearl / High-Yield Fact**
In patients with a metallic foreign body in the eye, it is essential to remember that the type of metal and its location can affect the approach to management. Iron and copper are the most common toxic metals, and their toxicity can lead to significant complications if not managed promptly.

**Correct Answer: D. Ultrasound examination. Ultrasound examination is not typically necessary for a metallic foreign body in the eye.**