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.
Maternal malnourishment (affects Vitamin A concentration in breastmilk).
Some of the more common causes of VAD are listed below: In the developed world, the leading causes of VAD are pancreatic, liver, and intestinal pathology. In resource-poor regions, the most common cause of VAD is insufficient nutrition complicated by chronic inflammation from regular gastrointestinal infections. VAD usually involves a malabsorptive process, such as inflammatory bowel disease or post-gastric bypass surgery, or a severely restrictive diet. VAD is especially prevalent in Africa and South-East Asia, where young children and pregnant women in low-income countries are disproportionally affected. The World Health Organization (WHO) estimates that 228 million children have VAD, causing 1-3 million childhood deaths and 5-10 million cases of eye disease. Although VAD is rarely seen in developed countries, it remains a public health concern in more than half of all countries, mostly affecting young children in impoverished regions. VAD is among the leading causes of blindness worldwide, estimated to blind half a million children each year. Unfortunately, xerophthalmia signifies a severity of VAD that causes significant morbidity and mortality from malnutrition and increased susceptibility to mucosal infections. Xerophthalmia continues to be a leading cause of preventable blindness in developing countries. Vitamin A serves several essential functions in the eye, and deficiency can lead to a constellation of ocular signs and symptoms that affect the conjunctiva, cornea, and retina. Xerophthalmia refers to the spectrum of ocular disease caused by severe Vitamin A deficiency (VAD).
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