Studies on Developing Retinal Vessels Vi. Histological Measurement of Fluoride-Induced Swelling in the Retina

IT is now a firmly established experimental finding that the vessels of the -immature retina specifically close as a result of raising the ambient oxygen concentration. Since this was first reported (Ashton, Ward, and Serpell, 1953) subsequent research has been directed towards the elucidation of the underlying mechanism. Some progress has been made, and it has recently been reported (Ashton, Graymore, and Pedler, 1957) that when certain established enzyme inhibitors were injected through the vitreous of an immature animal on to the retinal surface, complete obliteration of the retinal vasculature occurred within a short space of time. This effect was studied in the living animal, using a direct observation technique (Ashton and Cook, 1954; Pedler, 1957), and on repetition was found to be consistent, not only in the time elapsing between injection and vaso-obliteration, but also in the order of closure of the vessels concerned. These experiments have led to the formulation of a working hypothesis that the vessel closure observed might be caused by external pressure resulting from swelling of surrounding retinal tissue.