The reasons of blockage in the arterial network of the retina are various and they are being classified to the following categories: 
1.    Blockage due to rams
2.    Lumen stenosis and blockage due to atherosclerosis and thrombosis, arteriosclerosis, vasospasms or external pressure
3.    Irrigation decrease due to arterial hypertension (like after taking a PDES inhibitor e.g. Viagra) ocular hypertonia or blood dysplasia. 

The symptomology varies depending on the tracking of the blockage. The therapeutic treatment is doubted. The patients usually belong to the 5th or 6th decade of age and are people with weighed cardiovascular and cerebrovascular history. A detailed general examination has to be done always.