Evidence for functional endothelial cell damage in early diabetic retinopathy.

Two aspects of endothelial cell function were examined in two matched groups of male insulin-dependent diabetics, six with background retinopathy and seven without retinopathy. Leakage of fluorescein from the retinal capillaries was estimated by vitreous fluorophotometry. In addition, factors VIII/von Willebrand (vWF) and VIII-related antigen (VIII-RAG), which are synthesized by the endothelial cells, were measured, together with VIII-antihaemophilic factor (VIII-AHF). The patients without retinopathy had normal leakage of fluorescein in the macula (mean +/- SEM: 1.10 +/- 0.10 g X 10(-8)/ml) and the posterior vitreous (0.45 +/- 0.11 g X 10(-8)/ml), and normal circulating levels of vWF (123% of a normal reference plasma +/- 18%), VIII-RAG (137 +/- 14%) and VIII-AHF (112 +/- 18%). In contrast, the patients with background retinopathy showed higher leakage of fluorescein in the macula (6.34 +/- 1.74 g X 10(-8)/ml; p less than 0.01), and the posterior vitreous (3.09 +/- 0.94 g X 10(-8)/ml; p less than 0.02), as well as increased levels of vWF (177 +/- 16%; p less than 0.05). There was a trend towards increased VIII-RAG (195 +/- 24%; p less than 0.1), but not VIII-AHF (126 +/- 13%). Alterations of endothelial cell function thus accompany the development of retinopathy. It cannot be said from the present study whether these alterations also precede the appearance of retinopathy.

Vitreous fluorophotometry.

Vitreous fluorophotometry is as yet in its early phase of development, where probably many of the readings obtained represent artefacts. It is, however, a potentially exciting and useful clinical research tool which may indicate early changes in blood-retinal barrier function and which enables studies of fluid dynamics in the eye. Before it can be used extensively, more work on the development of reliable, uniformly acceptable equipment is necessary.