## **Core Concept**
Circumcorneal vascularization, also known as corneal neovascularization, refers to the growth of new blood vessels into the cornea from the limbal vascular plexus. This condition can be caused by various factors including nutritional deficiencies, inflammation, and corneal injury.

## **Why the Correct Answer is Right**
The correct answer, **Riboflavin (Vitamin B2)**, is linked to circumcorneal vascularization because riboflavin plays a crucial role in maintaining the health of the cornea and conjunctiva. A deficiency in riboflavin can lead to ocular manifestations, including corneal vascularization, as the vitamin is essential for energy production and can affect the integrity and function of the corneal tissue.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while Vitamin A deficiency can cause night blindness, xerophthalmia, and corneal ulcers, it is not primarily associated with circumcorneal vascularization.
- **Option B:** This option is incorrect as there is no well-known direct link between the listed vitamin and circumcorneal vascularization specifically related to the provided option text.
- **Option D:** This option is incorrect because, similar to option A, there is no direct association with circumcorneal vascularization as a primary manifestation.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that riboflavin deficiency can present with ocular symptoms such as blurred vision, and importantly, corneal vascularization. This is a critical point for exams as it highlights the importance of nutritional deficiencies in ocular health.

## **Correct Answer: C. Riboflavin.**