Explain Vitamin A Deficiency - Micronutrient Deficiencies?

Vitamin A deficiency (VAD) is a major public health problem, and the most vulnerable are preschool children and pregnant women in low income countries. In children, VAD is the leading cause of preventable severe visual impairment and blindness. An estimated 250 000 to 500 000 VAD children world over become blind every year, and about half of them die within a year. Vitamin A, we know, is essential for maintenance of healthy epithelium and normal vision. Deficiency of vitamin 'A' manifests in the form of eye lesions, which are grouped under 'xerophthalmia', can be either mild leading to night blindness and changes in conjunctiva (white of the eye) or in severe form causing damage to cornea (black of the eye) leading to irreversible blindness.