A Study to Evaluate ASP8232 in Reducing Central Retinal Thickness in Subjects With Diabetic Macular Edema (DME)

Inclusion Criteria: * Subject must have a documented diagnosis of type 1 or type 2 diabetes mellitus and a glycosylated hemoglobin A1c (HbA1c) of ≤ 12.0% at Screening * Subject has definite retinal thickening due to diffuse diabetic macular edema (DME) involving the central macula based on evaluating investigator's clinical evaluation and demonstrated by spectral domain-optical coherence tomography (SD-OCT) * Subject has central subfield thickness (CST) of at least 375 μm by SD-OCT with presence of intraretinal and/or subretinal fluid at screening visit and at the randomization visit * Subject has early treatment diabetic retinopathy study (ETDRS) best corrected visual acuity (BCVA) letter score ≤ 73 (Snellen 20/40) and ≥ 24 (Snellen 20/320) at screening visit Exclusion Criteria: * Subject's study eye has macular edema considered to be due to a cause other than DME * Subject's study eye has a decrease in BCVA due to causes other than DME that is likely to be decreasing BCVA by 3 lines or more * Subject's study eye has significant macular ischemia as shown on angiography * Subject's study eye has any other ocular disease that may cause substantial reduction in BCVA * Subject has active peri-ocular or ocular infection * Subject's study eye has a history of non-infectious uveitis * Subject's study eye has high myopia (-8 diopter or more correction) * Subject's study eye has a history of prior pars plana vitrectomy * Subject's study eye has a history of any ocular surgery within 3 months prior to Day 1 * Subject's study eye has a history of YAG capsulotomy within 3 months prior to Day 1 * Subject's study eye has a history of 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 through the Week 12 visit * Subject's study eye has a history of prior IVT, subtenon, or periocular, non-sustained release, steroid therapy within 3 months prior to Day 1 * Subject's study eye has a history of intravitreal sustained release dexamethasone therapy within 6 months prior to Day 1. * Subject's study eye has a history of intravitreal sustained release fluocinolone within 3 years prior to Day 1. * Subject's study eye has a history of prior treatment for DME with IVT anti-vascular endothelial growth factor (VEGF) treatment within 8 weeks prior to Day 1 * Subject has a history of prior treatment with any other (than previously listed) approved treatment which is not labeled for DME within 1 year prior to Day 1 * Subject's study eye has high-risk proliferative diabetic retinopathy (PDR) * Subject has uncontrolled glaucoma * Subject has media clarity, papillary constriction (i.e., senile miosis), or subject lacks cooperation that would interfere with any study procedures, evaluations or interpretation of data