**Core Concept**
The question requires knowledge of the application of fluorescent dyes in ophthalmology for diagnostic purposes. This involves understanding the use of intravenous or intraocular dyes to visualize retinal and choroidal vasculature, particularly in conditions like age-related macular degeneration (AMD) and diabetic retinopathy.

**Why the Correct Answer is Right**
The correct answer is **B. Sclera**. The dye is injected into the sclera, which is the white, fibrous, outer layer of the eyeball. This is done to visualize the choroidal vasculature, which is not directly accessible through the eye's anterior chamber. The dye then leaks into the choroid and is visible through the sclera, providing valuable information about the choroidal vasculature.

**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect because injecting the dye into the cornea would not allow visualization of the choroidal vasculature.
**Option C:** This is incorrect because injecting the dye into the vitreous would not provide a clear view of the choroidal vasculature, as the vitreous body is a clear gel-like substance that would obscure the view.

**Clinical Pearl / High-Yield Fact**
When using fluorescent dyes for ophthalmological diagnosis, it is essential to remember that the dye is injected into the sclera to visualize the choroidal vasculature, which is not directly accessible through the eye's anterior chamber.

**Correct Answer: B. Sclera**