Patients younger than 40-45 years of age with CRVO: Patients younger than 40-45 years of age with retinal vein occlusion and no known predisposing systemic disorder should undergo a comprehensive physical examination and testing for an underlying thrombotic tendency.

Unilaterally affected patients over age 45: Evaluation of unilaterally affected patients over age 45 should be individualized. Patients should be questioned regarding a previous history of a thromboembolic event or conditions such as vasculitis, collagen vascular disease, and myeloproliferative disease.

Patients with bilateral CRVO: All patients with bilateral retinal vein occlusion should undergo a complete physical exam and laboratory testing.

If the findings from the above studies are normal, functional and antigenic levels of fibrinogen and a thrombin time should be measured to exclude dysfibrinogenemia. Platelet aggregation studies and blood viscosity studies may be done also.

For venous or arterial thrombosis in young adults, the possibility of heterozygous homocystinuria should be considered. If high plasma levels of homocysteine are noted, the family members should be screened as well.