General Inclusion Criteria

• Age >= 18 years
• Diagnosis of diabetes mellitus (type 1 or type 2)
• Fellow eye (if not a study eye) meets criteria.
• Able and willing to provide informed consent. Study Eye Inclusion Criteria Subjects may have one or two study eyes. Subjects with two study eyes will be randomly assigned to receive sham injection at baseline and 4 weeks in one eye and either ranibizumab or triamcinolone in the other eye.
• Presence of severe nonproliferative or proliferative diabetic retinopathy for which investigator intends to complete panretinal photocoagulation within 49 days after randomization.
• Diabetic macular edema(DME) present on clinical exam and central subfield thickness on Optical Coherence Tomography (OCT) >250 microns, within 8 days of randomization.
• Best corrected Electronic-Early Treatment Diabetic Retinopathy Study visual acuity letter score >=24 (i.e., 20/320 or better), within 8 days of randomization.
• Media clarity, pupillary dilation, and subject cooperation sufficient to administer panretinal photocoagulation and obtain adequate fundus photographs and OCT.
• If prior macular photocoagulation has been performed, the investigator believes that the study eye may possibly benefit from additional focal photocoagulation.

General Exclusion Criteria

• Significant renal disease, defined as a history of chronic renal failure requiring dialysis or kidney transplant.
• A condition that, in the opinion of the investigator, would preclude participation in the study (e.g., unstable medical status including blood pressure, cardiovascular disease, and glycemic control).
• Participation in an investigational trial within 30 days of randomization that involved treatment with any drug that has not received regulatory approval at the time of study entry.
• Known allergy to any component of the study drugs.
• Blood pressure > 180/110 (systolic above 180 or diastolic above 110).
• Major surgery within 28 days prior to randomization or major surgery planned during the next 6 months.
• Myocardial infarction, other cardiac event requiring hospitalization, stroke, transient ischemic attack, or treatment for acute congestive heart failure within 4 months prior to randomization.
• Systemic anti-vascular endothelial growth factor(VEGF) or pro-VEGF treatment within 4 months prior to randomization.
• For women of child-bearing potential: pregnant or lactating or intending to become pregnant within the next 12 months.
• Subject is expecting to move out of the area of the clinical center to an area not covered by another clinical center during the 12 months of the study.

Study Eye Exclusion Criteria, Study eye only:

• Prior panretinal photocoagulation that was sufficiently extensive that the investigator does not believe that at least 1200 additional burns are needed or possible within 49 days after randomization.
• Macular edema is considered to be due to a cause other than diabetic macular edema.
• An ocular condition is present such that, in the opinion of the investigator, preventing visual acuity loss would not improve from resolution of macular edema (e.g., foveal atrophy, pigment abnormalities, dense subfoveal hard exudates, non-retinal condition).
• An ocular condition is present (other than diabetes) that, in the opinion of the investigator, might affect macular edema or alter visual acuity during the course of the study (e.g., retinal vein or artery occlusion, uveitis or other ocular inflammatory disease, neovascular glaucoma, etc.).
• Substantial cataract that, in the opinion of the investigator, is likely to be decreasing visual acuity by 3 lines or more (i.e., cataract would be reducing acuity to 20/40 or worse if eye was otherwise normal).
• History of treatment for DME at any time in the past 4 months (such as focal/grid macular photocoagulation, intravitreal or peribulbar corticosteroids, anti-VEGF drugs, or any other treatment).
• History of major ocular surgery (including vitrectomy, cataract extraction, scleral buckle, any intraocular surgery, etc.) within prior 4 months or anticipated within the next 6 months following randomization.
• History of Yttrium Aluminum Garnet capsulotomy performed within 2 months prior to randomization.
• Aphakia.
• Intraocular pressure >= 25 mmHg.
• History of open-angle glaucoma (either primary open-angle glaucoma or other cause of open-angle glaucoma; note: angle-closure glaucoma is not an exclusion criterion).
• History of steroid-induced intraocular pressure elevation that required intraocular pressure-lowering treatment.
• History of prior herpetic ocular infection.
• Exam evidence of ocular toxoplasmosis.
• Exam evidence of pseudoexfoliation.
• Exam evidence of external ocular infection, including conjunctivitis, chalazion, or significant blepharitis.

Fellow Eye Criteria

• Intraocular pressure < 25 mmHg.
• No history of open-angle glaucoma (either primary open-angle glaucoma or other cause of open-angle glaucoma; note: angle-closure glaucoma is not an exclusion criterion).
• No history of steroid-induced intraocular pressure elevation that required intraocular pressure-lowering treatment.
• No exam evidence of pseudoexfoliation.