Editor,—I read with interest the article by Iannaccone et al 1 on the connection between venous plasma endothelin-1 (ET-1) level and retinal vein occlusions (RVO). The authors conclude that elevated ET-1 concentration in the peripheral circulation in their patients may be a systemic marker for retinal venous occlusions. Also, they think it possible that the elevated ET-1 level they found in the peripheral blood samples could directly promote the development of retinal vascular occlusions (RVOs).

This latter conclusion seems to be unlikely since local retinal vasoconstriction is supposed to be influenced much more by the local ET-1 concentration than the elevation of the systemic venous ET-1 level. If elevated ET-1 concentrations in the peripheral circulation induce RVO, one would suppose it to be experienced in many RVO cases—for example, in normal pressure glaucoma, which is frequently associated with elevated plasma ET-1 values.2 3 On the contrary it is primary open angle glaucoma with elevated intraocular pressure and mild to moderate systemic hypertension that is frequently associated with RVOs.4 Both of these conditions are characterised by normal venous ET-1 concentrations.1 5These clinical considerations suggest that the direct influence of peripheral ET-1 levels on the retinal microcirculation is very unlikely.

The authors’ main conclusion that RVOs cause a significant elevation in peripheral venous ET-1 concentrations seems to be relevant. However, the authors should have shown some more data to exclude a few factors with a potential influence on their result. Was there any difference in the severity of systemic hypertension between hypertensive RVO patients and …