One of the earliest symptoms of Vit. A deficiency is:
Deficiency manifestations of Vitamin A: 

Night blindness (nyctalopia) is one of the earliest symptoms of vitamin A deficiency. 
The individuals have difficulty to see in dim light since the dark adaptation time is increased.
Prolonged deficiency irreversibly damages a number of visual cells.
Severe deficiency of vitamin A leads to xerophthalmia. This is characterized by dryness in conjunctiva and cornea, and keratinization of epithelial cells. 
In certain areas of conjunctiva, white triangular plaques known as Bitot's spots are seen.
lf xerophthalmia persisits for a long time, corneal ulceration and degeneration occur. 
This results in the destruction of cornea ,a condition referred to as keratomalacia, causing total blindness
Vitamin A deficiency blindness is mostly common in children of the developing countries

Key Concept:
Night blindness (nyctalopia) is one of the earliest symptoms of vitamin A deficiency.
Ref : Textbook of Biochemistry, Satyanarayana
Nyctalopia
Xerophthalmia
Bitot's spot
Keratomalacia