The knowledge of the individual collateral circulation is mandatory to judge the natural course and the prognosis of temporal branch vein occlusion. When collateral circulations are present a favourable final result can be anticipated even in cases with pronounced decreased visual acuity. To determine the time for coagulation treatment the differentiation between reversible and irreversible retinal lesions following branch vein occlusion is helpful. Particularly attention has to be paid to save those vessels, serving as a drainage function of the macula. On the other hand those neovascularisations have to be eliminated, leading ultimately to vitreous hemorrhage.