The cause of detached retina is not known. When vitamin E is deficient or when iron salts, which destroy this vitamin, are given to pregnant women, however, infants are often born prematurely and their retinas frequently become detached if they are exposed to an oxygen concentration greater than ordinary air. A few years ago, putting such babies in oxygen tents caused thousands to become permanently blind. This abnormality could be prevented by giving 150 milligrams of vitamin E daily starting immediately after birth or by breast milk, which supplies this vitamin. If vitamin E is inadequate, the essential fatty acids in the cells forming the walls of the capillaries in the retina--only one cell thick--are so harmed by oxygen that these cells disintegrate.