Besides the acute arterial occlusion and simple venous thrombosis, the clinical symptomatology may include signs of chronic arterial insufficiency, i.e. progressive blurring of vision, absolute visual field defects, cotton wool exudates, capillary occlusion and increased retinal circulation time. The poor visual prognosis is caused by progressive macular degeneration. In the case of acute arterial thrombosis, fragmentation of the blood column and absence of arterial pulsation are indicative of pronounced retinal ischemia. The ophthalmoscopic aspect of a visible embolus may be a hint for the prognosis of eventual recanalisation.