The interpretation of the pathogenesis of diabetic retinopathy has changed so much in the past twenty-five years that it is of interest to consider how and why this volution has occurred. In part the method of sectioning retinas on the flat and the newer staining and injection procedures have given a better picture of the vascular changes. In addition, ophthalmologists have always tried to determine whether findings in related specialties have an application to their problems, and thus advances made in pathology in general have suggested to thinkers in ophthalmology the possibility of applying such knowledge to their own field. We are indebted for much of our present-day concept of diabetic retinopathy to Friedenwald, Becker, Rich, McManus, Ballantyne, Loewenstein, and Ashton.
In recent years diabetic retinopathy has been on the increase, and if we are to get at the basic cause we must seek the reasons for the vascular involvement that is the basis of its development. The lengthening in life expectancy and the stress of present-day living probably do contribute to the increased incidence of visual loss, but if we are to gain in the prevention of blindness from diabetes we must try to remove or neutralize the fundamental pathology; namely, the involvement of the capillaries and venules which is the beginning of the trouble.
The characteristic vascular lesion of diabetic retinopathy consists of great numbers of minute saccular aneurysms in the retinal capillaries. Often the aneurysms are hyalinized. Two possibilities come to mind in regard to their formation: increased capillary pressure or histochemical changes that allow for the development of these aneurysms. In regard to the former, Friedenwald noted in studying histologic specimens of diabetic retinopathy that localized retinal venous occlusions were associated with abundant newly formed capillary collaterals. Aneurysms were not seen in these newly formed vessels, suggesting that increased capillary pressure is not in itself sufficient to cause the aneurysmal dilations.