The pathogenesis of proliferative diabetic retinopathy is unknown. Although there are some established clinical and histological facts, the exact sequence of events is yet to be determined. Diabetic angiopathy is widespread in the body and appears to be a complication ofand related to the duration of the diabetic state. The essential difference between this and proliferative diabetic retinopathy is the absence of microaneurysm formation and neovascularization outside the eye. It thus seems that local ocular factors, either genetic, metabolic, or anatomical, modify the generalized response. The role of the last factor has not yet been investigated, so that it is not known whether the anatomical pattern of the retinal arteries and veins has any relationship to the sites and size of areas of neovascularization.It is the purpose of this paper to study the size and distribution of those areas in early proliferative diabetic retinopathy which are of sufficient size to be visible in fundus photographs and to subject them to statistical analysis to see if any definable pattern emerges. Material103 patients with proliferative diabetic retinopathy are under regular review with regard to their diabetic state and in particular the fundus changes. 170 eyes in these patients were studied. All fundi were photographed in multiple fields using the Zeiss fundus camera at about 3-monthly intervals. The data collected in this survey are taken from these photographic records made at the first or second visits.Of the 170 eyes studied, 86 were suitable for inclusion in the present survey as the new vessels were in an early stage of formation. The remainder were excluded because the areas of proliferation were too diffuse and advanced at the initial visit and the origin of the new vessels was obscured or obliterated by connective tissue. The criteria for inclusion were: (i) There were good photographic records of the fundus at the first or second visit. (2) There was photographic continuity from the area of neovascularization to the optic disc, using one or more photographic fields.(3) The site of origin of an area of neovascularization was discrete, so that the relationship of the feeding vessels to the main retinal vein and the optic disc could be accurately measured. MethodA fixed projector was used to project the photographs a fixed distance onto a solid white wooden screen. All areas of neovascularization visible on the initial photographs were documented, thus giving a record of the lesions as they present to the ophthalmologist. A composite diagram was

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The name Simple (or Exudative) Diabetic Retinopathy includes a variety of diabetic changes, in particular, lipoid exudates, microaneurysms, and haemorrhages. The This investigation has been made retrospectively by the examination of serial fundus photographs taken over several years of patients suffering from bilateral simple diabetic retinopathy of varying degrees of severity. Clinical materialFifty eyes of 25 patients have been selected and studied by serial fundus photographs for periods of between 2 and 7 years. The average time of observation of each eye is 3-6 years and the interval between successive photographs rather less than 6 months. The general data (age, sex, duration of diabetes, etc.) are given in Table I and the details of the photographic observations in Table II. In order to confine the observations to the retinal changes, only eyes with clear media were included in this study. Some of the patients were included in a previous study as cases or controls in an investigation of the effects of a corn-oil diet (King, Dobree, Kok, Foulds, and Dangerfield, 1963).Ophthalmoscopic and other examinations were made at each visit of the patient, but the photographs form the basis of the data obtained. Although the resolution of the fundus camera is greatly inferior to that of the human eye, a permanent record which can be examined and re-examined and any lesion traced forwards or backwards in time is superior to purely visual records and is less liable to observer error.

The exudative lesions in diabetic retinopathy have received less attention than the more dramatic changes in the capillaries and veins which make up the characteristic fundus picture. Apart from the occasional fleck found in early cases of diabetic retinopathy the exudates appear in three main forms: a cluster of small deposits, a ring, and a large waxy-looking plaque.Serial fundus photographs taken at frequent intervals for 2 to 4 years have confirmed the observations of Whittington (1951), Larsen (1960), and other workers, that diabetic exudates disappear spontaneously. There are, however, differences in the evolution and devolution of the three types.(a) Cluster Form.-This is a collection of small white exudates giving a speckled appearance to a localized area of retina usually a half to one disc diameter in extent. It is often repeated in several parts of the posterior pole and is not generally associated with the normal vessels, aneurysms, or haemorrhages. This cluster form is the most transient type of exudative lesion, and we have observed it to appear and disappear in as short a period as 4 months.

Director of Research, Sir Stewart Duke-Elder ONE of. us has previously found (Thomassen, 194Tb) that the aqueous veins in eyes suffering from simple glaucoma convey little or no clear liquid when the bulbar tension is in an increasing phase, whereas the clear outflow through them is augmented when the bulbar tension is in a decreasing phase. The main intention of this paper is to extend this observation by means of photographs. Gartner (1944) and de Vries (1947) have already successfully photographed aqueouis veins. Those accompanying this paper were taken by the MIedical Illustration Department of the Institute of Ophthalmology. MethodThe bulbar tension was measured half hourly with a Schiotz X-tonometer.Before each measurement the eyes were anxesthetized with one drop 1 per cent. pantocain solution. By means of the repeated measurements it was possible to estimate whether 'the bulbar tension was increasing or decreasing. For further details concerning the estimation of the phases in the tension, the reader is referred to earlier explanations (Thomassen, 1947a; Thomnassen and Leydhecker, 1950). It is obvious that the repeated tonometry and the drops irritate the eye and therefore produce a generalized hyperxmia of the conjunctival vessels and aqueous veins. Observations and photographs have therefore been taken immediately before each new measurement, thus allowing time for the irritation from the previous measurements to subside.In some cases the observation, has been made difficult by another phenomenon. It has been found that the light from the slit-lamp can increase the amount of blood in the aqueous veins. In one case such a change was particularly striking. The patient, who had a simple glaucoma in both eyes, was observed on eight different days. In the left eye a large aqueous vein was seen with Blmost clear contents. When the light was switched on the speed of the current slowed down and after a short time the contents were rocking to and fro synchronously with the heart-beat. At the same time the vein was filling with blood. Finally, the contents of the vein, now onlv blood, were running quite freely in the direction opposite to that previously observed. After a short time in the dark the clear fluid was running as before, but