Venous thrombosis affects one in 1000 individuals per year12 causing significant morbidity and mortality. Inherited thrombophilia is a genetically determined tendency to thrombosis. Dominant abnormalities or combinations of mutations of varying penetrance giving rise to less severe defects may be suspected clinically from evidence of early age of onset, frequent recurrence, or family history. Milder traits may be discovered only by laboratory investigation. In most patients, however, thrombosis is episodic, separated by long asymptomatic periods. This episodic nature indicates that there is a trigger for each event and that the inherited trait requires interaction with other factors before a clinical disorder becomes apparent.

Vascular occlusions of the eye encompass thrombosis of retinal veins, arteries, and anterior ischaemic optic neuropathy. The Eye Disease Case Control Study Group identified a number of risk factors for branch, central, and hemiretinal vein occlusions including hypertension, diabetes, a history of cardiovascular disease, an increased body mass index at 20 years of age, and patients with open angle glaucoma.3-6 Branch retinal vein occlusions were particularly linked with hypertension. This echoed the findings of earlier smaller studies.78 In addition, hyperviscosity syndromes including a raised haematocrit and elevated erythrocyte aggregation rate, as well as other prothrombotic states (for example, hypofibrinolysis, increased levels of tissue factor), induced by increased levels of lipoprotein (a), malignancy, pregnancy, oestrogen therapy, and paroxysmal nocturnal haemoglobulinuria have all been associated with retinal vein occlusion.69-12

In addition to the factors described above, there are associations between retinal vein occlusions and inherited defects in the proteins of the coagulation pathways. Hypercoagulability can be the result of deficiencies in particular elements of the coagulation cascade such as protein C, protein S, or antithrombin III. Abnormal levels of the components of the fibrinolysis pathway also occur including tissue plasminogen activator, urokinase, …