Explain the Deficiency and Toxicity of vitamin A?

Who defines VAD as tissue concentrations of vitamin A low enough to have adverse health consequences even if there is no evidence of clinical xerophthalmia. Vitamin A deficiency (VAD) as you may already know leads to impairment in the vision severe infections and even death. It encompasses the full spectrum of clinical consequences associated with sub optimal vitamin A status. These disorders are known to include reduced immune competence resulting in increasedmorbidity and mortality largely from increased severity of infectious diseases night blindness corneal ulcers keratomalacia and related ocular signs and symptoms of xeropthalmia . Exacerbation of anacemia through sub optimal absorption and utilization of iron and other conditions not yet fully identified or clarified (e. g retardation of growth and development).

Xerophthalmia dryness of the eyes is the hallmark feature of clinical vitamin A deficiency and characterized by abnormalities of the conjunctive and cornea of eye. It has been classified into stages according to specific ocular manifestations as described herewith. One of the earliest manifestations of Xerophthalmia is right blindness (Stage XN). Individuals suffering from night blindness cannot see in dim light or around dusk. Subsequently, the conjunctiva, which is the thin transparent membrane that covers the cornea and lines the inside of the eyelid, becomes discoloured (muddy coloured), dry  and loses its brightness. This stage is known conjunctiva xerosis (Stage. XI A).  In addition to xerosis, dry, foamy, triangular spots may appear on the conjunctiva.  These are known as the Bitots spot (Stage XI B). Though conjunctiva changes in Xerophthalmia do not lead to blindness, they should be considered as warning signs.  If neglected, the changes may progress affecting the cornea causing corneal xerosi, s  (Stage X 2). In this condition, the cornea becomes dry and dull and appears like ground glass. This condition must be treated as an emergency. If it is not treated  immediately with vitamin A, the individual can develop ulcers (sores) in the cornea  (Stage XL3A - corneal ulceration  leading to the liquefaction of cornea, a condition  called keratomalace (Stage X3B). Increasing softening of the corneas may lead to corneal infection, rupture (perforation) and degenerative tissue changes. This condition inevitably leads to irreversible blindness. Past involvement causing corneal  ulcers stage XS) when healed leave white scars on the black portion of the eye  which can interfere with normal vision. A globe destroyed by advanced keratomalace is fundus (XF). In addition, thickening of the hair follicles (follicular- hyperkeratosis) is a cutaneous manifestation of vitamin A deficiency.