Vitamin C contributing to the more severe symptoms of scurvy. More generally, the biochemical role of vitamin C is to act as an antioxidant (a reducing agent) by donating electrons to various enzymatic and non-enzymatic reactions. Doing so converts vitamin C to an oxidized state - either as semidehydroascorbic acid or dehydroascorbic acid. These compounds can be restored to a reduced state by glutathione and NADPH-dependent enzymatic mechanisms. In plants, vitamin C is a substrate for ascorbate peroxidase. This enzyme utilizes ascorbate to neutralize toxic hydrogen peroxide (HO) by converting it to water (HO). Scurvy is a disease resulting from a deficiency
Vitamin A deficiency conjunctiva, known as Bitot's spots, can be seen. ; Imtiaz's sign is the earliest ocular sign of VAD. Conjunctival epithelial defects occur around lateral aspect of the limbus in the subclinical stage of VAD. These conjunctival epithelial defects are not visible on a biomicroscope, but they take up black stain and become readily visible after instillation of kajal (surma); this is called "Imtiaz's sign". VAD can also lead to impaired immune function, cancer, and birth defects. Vitamin A deficiency is one of several hypovitaminoses implicated in follicular hyperkeratosis. Night blindness is the difficulty for the eyes to adjust to dim