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Chapter 7
iNTRODUCTION
Vitamin A deficiency is a major cause of preventable blindness in the
world' especially in the third world countries. The problem is common
in pre-school and school-age children. It has been estimated that up to
100,000 children become blind from vitamin À deficiency every year
(McLaren, 1965). Nutrition intervention programs, which include activites
to detect hypovitaminosis À (vitamin A deficiency) among children,
could reduce the prevalence of xerophthalmia and blindness among populations
at risk.
The earliest clinical sign of hypovitaminosis À is night blindness.
Night blindness is a decrease in the retinal sensitivity to light under
dinr light condition (a decrease in dark adaptation ability).
External
synptoms of hypovitaminosis À, such as corneal, and conjunctival xerosis
and Bitot's spotsr câIl not be used to detect early hypovitaminosis À,
since these symptoms are not reflected during the early stages of development
of the deficiency. Serum retinol (the active forn of Vitamin A
in the blood) level is not a reliable measure of early hypovitaminosis À
in individual subjects because of the wide range of border-line values
where viLamin A dependent rod function may or ¡nay not be affecÈed
(carney and Russel1, 1980). Moreover, serum retinol revels could be
affected by a lack of Retinol Binding Prolein even when liver retinol
stores are adequate (pitt, i981). A culturally based history of dark
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