The retinal vasculature of postmortem normal human and diabetic
eyes was studied using an
immunohistochemical technique in conjunction with confocal laser scanning
microscopy. The technique,
which stained for von Willebrand factor, allowed both large areas of the
retinal vasculature to be visualised
and abnormalities to be studied in detail without disturbing the tissue
architecture. Only one
microaneurysm, defined as any focal capillary dilation, was observed in
10 normal eyes but numerous
microaneurysms were seen in 4 out of 5 diabetic retinas; counts varied
between 0 and 26 per 0.41 mm2
sample area. Microaneurysms were classified into 3 categories according
to morphology: saccular, fusiform
and focal bulges. Most were saccular, these having no preferred orientation.
The majority of
microaneurysms were associated with just 2 vessels suggesting they were
unlikely to develop at vascular
junctions. The majority were observed to originate from the inner nuclear
layer and were therefore in the
deeper part of the inner retinal capillary plexus. Variation in the staining
of microaneurysms may correlate
with endothelial dysfunction seen clinically as dye leakage during fluorescein
angiography.