**Core Concept**
Fluorescein dye is a type of fluorescent compound used in medical imaging and diagnostics, particularly in ophthalmology and otolaryngology. It is a water-soluble, non-toxic dye that emits light at a specific wavelength when excited by ultraviolet or blue light.

**Why the Correct Answer is Right**
Fluorescein dye is primarily used to stain the corneal and conjunctival vessels, allowing for visualization of the vascular patterns and detection of any abnormalities such as neovascularization or leakage. The dye is absorbed by the endothelial cells of the cornea and conjunctiva, and its fluorescence is then visualized using a cobalt blue filter, which excites the dye and causes it to emit a greenish-yellow light. This allows for detailed examination of the ocular surface and detection of conditions such as corneal ulcers, conjunctivitis, and dry eye syndrome.

**Why Each Wrong Option is Incorrect**
**Option A:** Fluorescein dye is not used to stain skin structures.
**Option B:** Indocyanine green dye is used for choroidal neovascularization imaging, not fluorescein.
**Option C:** Trypan blue dye is used to stain dead cells, not corneal or conjunctival vessels.

**Clinical Pearl / High-Yield Fact**
It is essential to note that fluorescein dye is contraindicated in patients with known allergies to fluorescein or sulfonamides, as well as in patients with corneal ulcers or other ocular surface abnormalities.

**Correct Answer:** B.