This study is designed to evaluate the efficacy of intravitreal Ranibizumab in comparison with macular laser photocoagulation as treatments for macular edema secondary to branch retinal vein occlusion.

Characteristics of this study is as below

1. Multicenter, randomized clinical trial. (intravitreal Ranibizumab 0.5mg injection vs. macular laser photocoagulation)
2. After 48 weeks follow up, functional change(visual acuity)and anatomical change (central retinal thickness) would be evaluated

Inclusion Criteria:

• Symptom duration < 6 Months, > 4 weeks
• Visual acuity - less than 20/40 (73 letters) more than 20/400 (19 letters) in ETDRS chart
• OCT - center involved retinal thickening : > 250 micrometers
• clear media
• well controlled hypertension (<140/90mmHg) and diabetes (6.5<HbA1c<9.5)
• willing to return for all scheduled visits

Exclusion Criteria:

• uveitis,NVG, exudative AMD, diabetic retinopathy, Irvine-Gass syndrome, OIS
• any malignancy
• previous treatment history - laser photocoagulation, intravitreal injection with any drug, vitrectomy
• vitreomacular traction or epiretinal membrane
• intraocular surgery in the study eye within 6 months
• uncontrolled glaucoma ( > 30mmHg with anti-glaucoma medications)
• optic neuropathy, amblyopia
• A condition that in the opinion of the investigator would preclude a patient's participation in the study