Severe corneal xerosis progressing to keratomalacia. Night blindness is considered to be both a sensitive and specific indicator for serum retinol levels. Children may not be able to verbalize their symptoms, and parents need to be asked if they have noticed their children behaving differently in the dark, e.g. Although it is considered one of the earliest manifestations, children with VAD may develop one of the more severe signs, such as corneal ulcers, after infection or diarrhea without any of the classically early signs. Night blindness (Grade XN): Defective vision in dim light or night blindness is one of the most common manifestations of VAD, especially in children age 2-6 or pregnant or lactating women. Retinol is a vitamin A-derived cofactor that is required for the formation of rhodopsin thus, VAD leads to impairment of rod function and causes nyctalopia, or night blindness due to the eye’s inability to adapt from light to dark. Rods have a singular photopigment, rhodopsin. Rods are the retinal photoreceptor that is responsible for night vision. VAD causes metaplasia and keratinization of mucus-secreting epithelium, which can cause conjunctival and corneal xerosis, corneal ulcers, keratomalacia, and corneal scarring. In the eye, Vitamin A is essential for maintenance of conjunctival and corneal epithelia as well as night vision. Children aged 1-5 years old require a minimum of 200ug/day to prevent symptomatic VAD. For children and pregnant or lactating women, the recommended amount is 300-900, 770, and 1300ug/day, respectively. The recommended dietary allowance of vitamin A is 700ug/day in females and 900ug/day in the males. Disruption in any of these processes can lead to VAD. Stored vitamin A is released into the circulation bound to prealbumin (transthyretin) and retinol-binding protein. The liver stores 80-90% of the body’s vitamin A in hepatic stellate cells, and the remainder is stored in adipose tissue and the pancreas. Once consumed, Vitamin A is hydrolyzed by pancreatic and intestinal enzymes, emulsified with dietary fats and bile acids, and absorbed in the duodenum. These include green leafy and yellow vegetables, carrots, and deep- or bright-colored fruits. A variety of other foods contain beta-carotene and other provitamin carotenoids, which get converted into vitamin A. It has several essential functions in the body, including cell development, metabolism, immune function, vision, and reproductive function.ĭietary sources of preformed vitamin A include dark leafy greens, orange-colored vegetables, fish liver oils, liver, egg yolks, butter, and vitamin A-fortified dairy products. Vitamin A is a fat-soluble vitamin that humans derive primarily from diet.
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