This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
[{'content': "One of the earliest symptoms of Vit. A deficiency is: \nSelect and explain. \nA. Nyctalopia, B. Xerophthalmia, C. Bitot's spot, D. Keratomalacia", 'role': 'user'}, {'content': "Answer: A \nExplanation: Deficiency manifestations of Vitamin A:\xa0\n\nNight blindness (nyctalopia) is one of the earliest symptoms of vitamin A deficiency.\xa0\nThe individuals have difficulty to see in dim light since the dark adaptation time is increased.\nProlonged deficiency irreversibly damages a number of visual cells.\nSevere deficiency of vitamin A leads to xerophthalmia. This is characterized by dryness in conjunctiva and cornea, and keratinization of epithelial cells.\xa0\nIn certain areas of conjunctiva, white triangular plaques known as Bitot's spots are seen.\nlf xerophthalmia persisits for a long time, corneal ulceration and degeneration occur.\xa0\nThis results in the destruction of cornea ,a condition referred to as keratomalacia, causing total blindness\nVitamin A deficiency blindness is mostly common in children of the developing countries\n\nKey Concept:\nNight blindness (nyctalopia) is one of the earliest symptoms of vitamin A deficiency.\nRef : Textbook of Biochemistry, Satyanarayana", 'role': 'assistant'}]