Vitamin A deficiency is a condition in which an individual does not have a sufficient amount of vitamin A in their body. Vitamin A helps develop and maintain mucous membranes, healthy teeth, soft tissue, skeletal tissue, and the retina. There are three different forms of vitamin A, including carotenoids, retinol, and beta carotenes. Vitamin A deficiency can occur when an individual's body is unable to absorb fats from consumed food, or when their metabolism has become altered. A lack of vitamin A ingestion can also result in this type of deficiency. It is recommended that children consume between three and six hundred micrograms of vitamin A per day, while adults are recommended to have between seven and nine hundred micrograms daily. Vitamin A deficiency can be diagnosed with a physical examination, blood tests, electroretinography, and treatment trials.
Night blindness, also known as nyctalopia, is where an individual cannot see properly in conditions of dark or dimly lit environments, including at night. An individual's retina must function properly to enable them to see correctly in low light. The retina is made up of light-sensitive cells called rods and cones that contain substances called photopigments, which are responsible for communicating light to the brain. The photopigment most associated with night vision is called rhodopsin. When an individual moves from a lighted environment to a darker environment, the photopigments undergo a process referred to as dark adaptation. However, an abundant supply of vitamin A is required for rhodopsin to become activated in dark adaptation. In vitamin A deficiency, rhodopsin is unable to interact with the brain, and dark adaptation does not occur to the extent that would produce adequate night vision. Nyctalopia is one of the first symptoms to manifest in individuals who are vitamin A deficient.