HYPOVITAMINOSIS A (aVITAMINOSTS a) 601 



human subjects exhibited an appreciable diminution of plasma vitamin A. 

 Within three months ^'alues of 40 I.U./IOO ml. were noted, but only in the 

 case of three subjects. One man, however, showed no appreciable de- 

 crease, e\'en after twenty-two months of deprivation. Some additional 

 data have beeii made available in nutrition surveys and cUnicopathologic 

 studies. 



c. Effects of Vitamin A Deficiency in Man. (a) Night Blindness. The 

 inabilit}' to see in dim light represents one of the oldest recognized diseases 

 known to man; it was early shown to respond to treatment with liver. 

 It is now recognized that vitamin A in the form of ^^tamin A aldehyde 

 (retinene) comprises the most important part of the visual purple, which is 

 made up of the retinal pigments. Rhodopsin and porphyropsin are pres- 

 ent in the rods, while iodopsin occurs in the cones. These retinal pigments 

 are readily broken down when exposed to light, and they can then be regen- 

 erated in the dark. New retinene can be formed from vitamin A by the 

 retinene reductase system, in which DPN is a coenzjTne. 



When the amount of \atamin A available in the plasma is decreased, it 

 would be expected that the regeneration of the ^dsual purple would be de- 

 layed. In order to estimate the speed of the regeneration, which can be 

 employed as an index of vitamin A requirements, various types of biopho- 

 tometers and adapt ometers have been employed to determine the so-called 

 "dark adaptation time." These instruments afford a reliable measure- 

 ment of dark adaptation except where the ^^sual defect is minimal. ^°®*~^°^* 



(6) Xerophthalmia and Keratomalacia. Xerophthalmia is manifested 

 by a roughened state (or xerosis) of the conjunctiva and cornea. It is 

 often associated with the presence of irregular whitish plaques (the so- 

 called Bitot's spots) on the scleral conjunctiva. When the condition pro- 

 gresses further, and is associated with edema, infiltration, and necrotic 

 softening of the cornea, which may be followed by perforation, hjTDopyon 

 and panophthalmitis, the syndrome is referred to as keratomalacia. 



These disorders of the eye have been recognized for about one hmidred 

 years, during which time their frequent association with night blindness was 

 recognized. It was also known that liver and cod liver oil were effective 

 curative agents. In 1863, Bitot^"^^ first described the whitish plaques on 

 the corneoconjunctival mucosa, occurring in association with night bhnd- 

 ness. He described them as "hemeralopic plaques." They were success- 



'««3 E. L. Blanchard and H. A. Harper, Arch. Internal Med., 66, 661-669 (1940). 

 «»«* P. C. Jeans, E. L. Blanchard, and F. E. Satterthwaite, /. Pediat., 18, 170-194 

 (1941). 



■o^* R. E. Eckardt and L. V. Johnson, /. Pediat., 18, 195-199 (1941). 

 ""'« P. Bitot, Gaz. med. Paris, 18, 435-438 (1863). 



