**Core Concept**
Circumcorneal vascularization refers to the growth of blood vessels on the limbus, the border of the cornea, which can be a sign of various ocular and systemic conditions. Vitamin deficiencies can lead to changes in the cornea, potentially triggering vascularization.

**Why the Correct Answer is Right**
The correct answer is **B. Riboflavin (B2) deficiency**. Riboflavin is essential for maintaining the integrity of the corneal epithelium. A deficiency in riboflavin can lead to corneal vascularization, including circumcorneal vascularization. This is because the cornea lacks blood vessels in a healthy state, and a deficiency in riboflavin can disrupt this barrier, allowing vessels to grow onto the cornea.

**Why Each Wrong Option is Incorrect**
* **Option A:** Vitamin A deficiency primarily causes night blindness, dry skin, and impaired immune function, but it is not typically associated with circumcorneal vascularization.
* **Option C:** Vitamin C deficiency (scurvy) can cause various ocular symptoms, including conjunctival hemorrhages, but it is not specifically linked to circumcorneal vascularization.

**Clinical Pearl / High-Yield Fact**
Riboflavin deficiency can also cause angular cheilitis, a condition characterized by inflammation and cracking at the corners of the mouth.

**Correct Answer:** B. Riboflavin deficiency.