NIGHT BLINDNESS.

Auckland Star, Volume LXV, Issue 267, 10 November 1934, Page 10 (Supplement)

NIGHT BLINDNESS.

CURIOUS VISUAL DEFECT. HOW IT CAN BE CTTRED. DIETARY EFFECT ON RETINA. Back of the eye is the retina. It is upon its outer layer, which is the one furthest from the lens of the eye, that images are formed. Hence light must pass through all the other layers before it reaches the sensitive area. Rods and cones constitute this sensitive layer. Each rod (but not each cone) is tipped with a rose-coloured substance which is called visual purple and which is sensitive to light. Step from bright sunlight into a dark room. At first you see nothing. Gradually objects become dimly visible — chairs, tables, bookcases. Your pupils are dilated. More light falls on the outer part of the retina, the region of the rods. The visual purple on the rods is decomposed or bleached. You see. Darkness has the property of regenerating visual purple and thus making it serviceable again. When visual purple fails to regenerate, the all'liction known as night blindness results. For some years it has been known that the cause is a deficiency of vitamin A. As far back as 1925 Drs. Fridericia and Holm proved this fact by experimenting with, rats starved of vitamin A. War Prisoners Affected. During the World War Austrian prisoners of war in Russia fell victims to night blindness. Austrian j'hysicians, themselves prisoners, began to inquire. They found the disorder common among Russian peasants, especially during Easter. The religious diet then enjoined is strictly vegetarian. Even the fats and oils must be of vegetable origin. Partly cooked liver or cod-liver oil were the popular remedies for the disease. Their effect was striking. In a few days there were complete cures. In Japan the same story is told. In February and March night blindness is sure to break out among Japanese railway workers in Manchuria. Fish is then scarce and expensive. In April, when the patch is large and prices fall, night blindness disappears. With this background we begin to understand the importance of the announcement that Dr. George Wald made at Woods Hole, Massachusetts recently. Visual Purple Analysed. What Dr. Wald did was to analyse visual purple chemically. A difficult task at best because of the highly complex nature of the compound, it was to a certain extent simplified because he knew for what he was looking. When visual purple bleached, something yellow split off. The something turned out to be carotene, which either contains vitamin A or is very closely related to it. At any rate night blindness can be cured by giving sufferers sliced carrots, in which, as might bo supposed, carotene and vitamin A are found. Even more important is the fact that Dr. Wald actually saw carotene converted into vitamin A in the retina of the eye. — W. Kaeinpffert in "New York Times."