STUDIES ON THE MECHANISM OF RETINAL NEOVASCULARIZATION: ROLE OF LACTIC ACID

ACCORDING to Michaelson (1948, 1954), neo-vascularization is due to an unknown vasoproliferative factor that appears in the tissues in hypoxic conditions.This factor is supposed to be responsible for the development of embryonic retinal vessels and for pathological neovascularization.The role of hypoxia in vascularization is confirmed by observations that areas of the retina well supplied with oxygen, such as the outer layers, macula lutea, and the neighbourhood of arteries, contain no vessels and that at the beginning of vascu- larization hypoxic conditions prevail in the inner retinal layers.At that stage of development the retina thickens and its inner layers become insufficiently supplied with oxygen.Campbell (1951) and Ashton and Cook (1954) showed in animal experiments that the width of the avascular zone in the neighbourhood of retinal arteries depends on the oxygen tension.At higher oxygen concentrations a wide zone (and, alternatively, at lower oxygen concentrations a narrow zone) developed.With high oxygen tension, Ashton, Ward, and Serpell (1953Serpell ( , 1954)), Michaelson, Herz, Lewkowitz, and Kertesz (1954), and Ashton and Blach (1961) were able to cause obliteration of the vessels in the immature retina of newborn animals.Ashton and others (1954) found that high concentrations of oxygen caused obliteration in the retinal arteries, while the subsequently applied lower oxygen tension induced re- vascularization.Michaelson (1954), Ashton (1957), and Eliasoph (1957) described an association between the formation of a vasoproliferative factor and the increase of anaerobic metabolic products.Ashton summarized the conditions for neovascu- larization as follows: