A child with dry skin and scaling is suspected of having vitamin A deficiency. What is the earliest feature of vitamin deficiency?

The earliest manifestations of vitamin A deficiency are ocular changes. Impaired dark adaptation (nyctalopia), is followed by xerophthalmia, and as corneal keratin desquamates and overgrowth of Corynebacterium xerosis on the sclera occurs, white patches known as Bitot spots develop. Severe deficiency may lead to corneal xerosis, ulceration, and keratomalacia, which may result in corneal perforation, prolapse of the iris, and blindness. Ref: Jen M., Yan A.C. (2012). Chapter 130. Cutaneous Changes in Nutritional Disease. In K. Wolff (Ed), Fitzpatrick's Dermatology in General Medicine, 8e.