The purpose of this study is to evaluate the safety and efficacy of AKB-9778 administered as daily subcutaneous injections with and without monthly intravitreal injections of ranibizumab for 3 months in patients with diabetic macular edema.

The following is an abbreviated list of inclusion criteria:

• Adults between 18 to 80 years of age, inclusive
• Diagnosis of diabetes mellitus (type 1 or type 2)
• Decrease in vision in the study eye determined to be primarily the result of DME
• Definite retinal thickening due to diffuse DME involving the central macula in the study eye
• Central subfield thickness of at least 325 µm by sdOCT with presence of intraretinal fluid in the study eye
• ETDRS BCVA letter score ≤ 76 and ≥ 24 in the study eye

The following is an abbreviated list of exclusion criteria:

• Hemoglobin A1C (HbA1C) ≥ 12.0% at Screening

• History of non infectious uveitis

• Decrease in visual acuity due to causes other than DME in the study eye

• History of any of the following in the study eye (however, the following are not exclusionary in the fellow eye):

  1. Prior pars plana vitrectomy
  2. Any ocular surgery within 3 months prior to Day 1
  3. YAG capsulotomy within 3 months prior to Day 1
  4. Panretinal scatter photocoagulation (PRP) or focal laser within 3 months prior to Day 1 or anticipated need for PRP during the course of the study
  5. Prior intravitreal, subtenon, or periocular steroid therapy within 3 months prior to Day 1
  6. Prior treatment with intravitreal anti-vascular endothelial growth factor (VEGF) treatment within 8 weeks prior to Day 1