**Core Concept**
The tear film integrity is crucial for maintaining clear vision, and assessing its integrity is essential in diagnosing and managing ocular surface disorders. The tear film is a complex structure composed of mucins, lipids, and water, and its integrity is tested using specific stains that highlight its components.

**Why the Correct Answer is Right**
The correct answer is **B. Rose Bengal stain**. Rose Bengal stain is a vital dye used to assess the integrity of the tear film. It stains damaged or abnormal cells in the ocular surface, including the conjunctiva and cornea. The stain accumulates in areas with reduced tear film, such as in dry eye syndrome or ocular surface diseases. The intensity of the stain can help clinicians evaluate the severity of the condition and guide treatment.

**Why Each Wrong Option is Incorrect**
* **Option A:** is incorrect because it does not specifically target the tear film integrity.
* **Option C:** is incorrect because it is not commonly used to assess tear film integrity.

**Clinical Pearl / High-Yield Fact**
Rose Bengal stain is a valuable tool in diagnosing and managing ocular surface disorders. It is essential to note that Rose Bengal stain can also be used to assess the integrity of the corneal epithelium and to diagnose conditions such as dry eye syndrome.

**Correct Answer: B. Rose Bengal stain**