VASCULAR OCCLUSION IN DIABETIC-RETINOPATHY - A QUALITATIVE AND QUANTITATIVE HISTOPATHOLOGICAL STUDY

The retinal vessels from seven diabetic patients and from six age-matc hed normal controls were studied qualitatively and quantitatively usin g various histological staining techniques. In diabetic patients the w alls of retinal arterioles and capillaries showed significantly more s taining than normals for periodic acid Schiff (neutral glycoproteins), Sirius red (connective tissue), and for Alcian blue at pH 2.6, pH 5.8 and at pH 5.8 combined with MgCl2 in concentrations less than 0.9 NI (acid mucopolysaccharides). In the retina from diabetic patients there was no difference between the number of capillaries staining with the se dyes in areas of vascular occlusion and in adjacent control areas. Furthermore, in areas of vascular occlusion, the material accumulated centrally to occlude the lumen of ghost vessels did not stain with any of the dyes used. A homogenous material, accumulated in the outer ret ina in areas of vascular occlusion in the retina from diabetic patient s, only stained with Alcian blue at pH 5.8 combined with MgCl2 in conc entrations less than 0.4 M, suggesting a different molecular compositi on from the Alcian blue material accumulated in the retinal vascular w alls. The findings are in accordance with the knowledge that basement membranes of retinal vessels are thickened in diabetes mellitus. Howev er, the findings also indicate that basement membrane thickening canno t fully account for vascular occlusion in diabetic retinopathy.