Editor,—We read with great interest the article by Foss and associates published in the March issue of theBJO.1

In discussing different techniques for the detection of vascular structures in uveal melanomas, it is obviously necessary to avoid a misinterpretation of the pertinent criteria:

(1) Foss and associates interpreted the areas 1 and 2 shown in Figure 1A of their article as “area of silence”, and “area of normal vasculature”. We would not have classified the region marked as 1 in Figure 1A as a “silent area”, because many small vessels with a “white” lumen and a very thin PAS positive basement membrane can be identified, even at the magnification and the weak PAS stain given in their article. In addition, the two enlarged vessels marked as 2 would not have been classified as “normal” according to our original description.2-4 Therefore, we were not surprised that the authors could demonstrate a positive staining for vascular endothelium using factor VIII in Figure 1B. In our view, Foss and associates just misinterpreted findings with their PAS technique, which led to a misleading conclusion.

(2) Furthermore, in our experience we find it relatively easy to discriminate between basement membrane material and connective tissue as shown in Figure 2. In cases of doubt, we always stained serial sections for connective tissue using the Gomori’s trichrome stain. Blood vessels within a tumour contain endothelial cells, a basement membrane, and a lumen sometimes with detectable erythrocytes. This lumen can be identified in most of the tumour blood vessels using the PAS staining technique. In cases of doubt, the PAS stain could be compared with the adjacent haematoxylin and eosin stain of serial sections in order to identify a lumen and/or erythrocytes within a vessel lumen. The ultrastructure of the tumour blood …