**Core Concept:**
Keratomalacia is a clinical entity that occurs due to severe vitamin A deficiency, leading to impaired corneal epithelial cell proliferation and differentiation, ultimately causing corneal edema, cloudiness, and impaired vision. Vitamin A plays a crucial role in maintaining corneal health and vision.

**Why the Correct Answer is Right:**
Vitamin A deficiency is the primary cause of keratomalacia. When there is a severe deficiency of vitamin A, the corneal epithelial cells fail to proliferate and differentiate properly, leading to impaired corneal healing and desquamation. This results in corneal edema, cloudiness, and vision impairment. Vitamin A deficiency affects the corneal epithelium, specifically the corneal limbal stem cells, which are essential for maintaining the corneal health and vision.

**Why Each Wrong Option is Incorrect:**

A. Vitamin D deficiency (Option A) does not directly affect corneal health and vision, making it an incorrect choice.

B. Vitamin C deficiency (Option B) also does not directly affect corneal health and vision, making it an incorrect choice.

C. Vitamin E deficiency (Option C) does not directly affect corneal health and vision, making it an incorrect choice.

D. Calcium deficiency (Option D) does not directly affect corneal health and vision, making it an incorrect choice.

**Clinical Pearl / High-Yield Fact:**
Vitamin A deficiency is a critical public health issue affecting millions of children globally. Prevention and early intervention are essential to prevent blindness and other severe consequences of vitamin A deficiency. Promoting balanced diets rich in vitamin A-containing foods, such as liver, fish, eggs, and fruits (carotenoids), is a crucial step in addressing this issue. Additionally, supplementation programs have proved effective in preventing blindness and improving overall health outcomes.