Eyetech Pharmaceuticals Inc. and Pfizer, Inc. are studying an investigational drug, MacugenTM, for the possible treatment of CRVO. An investigational drug is one that has not been approved by the U.S. Food and Drug Administration (FDA). This investigational drug may slow the growth of abnormal blood vessels in the eye and may reduce tissue swelling in the eye.

The purpose of this study is to compare the safety and efficacy of a Macugen™ injection to a "pretend" injection. In addition, the purpose of this study is to measure the action of the study drug in the body over a period of time and to check for the presence of the study drug in your blood (called pharmacokinetics or PK).

This study will involve approximately 90 people. People who decide to participate will have an equal chance (1 in 3) to receive one of three study injections, two of which are Macugen™ and one of which is a "pretend" injection.

This study will consist of 3 phases: a screening phase which will last up to two weeks, a confirmation phase which will last one day, and a randomization phase (the patient will be assigned by chance to a study group in this phase) which will last approximately 52 weeks.

Inclusion Criteria:

• CRVO must have occurred within the past 6 months and be associated with macular edema determined by OCT.
• Vision in the study eye corresponding to between approximately 20/50 to 20/400 and better than or equal to approximately 20/200 in the fellow eye.

Exclusion Criteria:

• Presence of signs of old branch retinal vein occlusion (BRVO) or CRVO in the study eye or any other retinal vascular disease including diabetic retinopathy.
• Vitreous hemorrhage except breakthrough hemorrhage from intraretinal hemorrhage.
• Prior pan retinal photocoagulation (PRP) or sector scatter photocoagulation.