Xerophthalmia from hypovitaminosis A is specifically due to lack of the hormone-like vitamin A metabolite retinoic acid, since (along with certain growth-stunting effects) the condition can be reversed in vitamin A deficient rats by retinoic acid supplementation (however the retinal damage continues). Since retinoic acid cannot be reduced to retinal or retinol, these effects on the cornea must be specific to retinoic acid. This is in keeping with retinoic acids known requirement for good health in epithelial cells, such as those in the cornea. Cause
The condition is not congenital and develops over the course of a few months as the lacrimal glands fail to produce tears. Other conditions involved in the progression already stated include the appearance of Bitots spots, which are clumps of keratin debris that build up inside the conjunctiva and night blindness, which precedes corneal ulceration and total blindness. Classification
World Health Organization classified xerophthalmia into following stages:
XN-Night blindness
X1A-Conjunctival xerosis
X1B-Bitot spots
X2-Corneal xerosis
X3A-Corneal ulceration/keratomalacia, involving less than one-third of the cornea
X3B-Corneal ulceration/keratomalacia, involving more than one-third of the cornea
XS-Corneal scar due to xerophthalmia
XF-Xerophthalmic fundus

Prevention
Prophylaxis consists of periodic administration of Vitamin A supplements.
Xerophthalmia (from Ancient Greek "xērós" (ξηρός) meaning "dry" and "ophthalmos" (οφθαλμός) meaning "eye") is a medical condition in which the eye fails to produce tears. It may be caused by vitamin A deficiency, which is sometimes used to describe that condition, although there may be other causes. Xerophthalmia caused by a severe vitamin A deficiency is described by pathologic dryness of the conjunctiva and cornea. The conjunctiva becomes dry, thick and wrinkled. The first symptom is poor vision at night. If untreated, xerophthalmia can lead to dry eye syndrome, corneal ulceration, and ultimately to blindness as a result of corneal and retinal damage. Xerophthalmia usually implies a destructive dryness of the conjunctival epithelium due to dietary vitamin A deficiency—a rare condition in developed countries, but still causing much damage in developing countries. Other forms of dry eye are associated with aging, poor lid closure, scarring from a previous injury, or autoimmune diseases such as rheumatoid arthritis and Sjögrens syndrome, and these can all cause chronic conjunctivitis. Radioiodine therapy can also induce xerophthalmia, often transiently, although in some patients late onset or persistent xerophthalmia has been observed.The damage to the cornea in vitamin A associated xerophthalmia is quite different from damage to the retina at the back of the globe, a type of damage which can also be due to lack of vitamin A, but which is caused by lack of other forms of vitamin A which work in the visual system.