The purpose of this study is to evaluate efficacy and safety of ASP8232 in subjects with diabetic macular edema (DME). This study will evaluate the percent change from baseline in excess central subfield thickness (CST) in the study eye as assessed by spectral domain-optical coherence Tomography (SD-OCT) for ASP8232 monotherapy at Month 3.

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

Access to anonymized individual participant level data collected during the study, in addition to study-related supporting documentation, is planned for studies conducted with approved product indications and formulations, as well as products terminated during development. Studies conducted with product indications or formulations that remain active in development are assessed after study completion to determine if Individual Participant Data can be shared. Further details on Astellas' data sharing policy can be found at https://www.clinicaltrials.astellas.com/transparency/.

Access to participant level data is offered to researchers after publication of the primary manuscript (if applicable) and is available as long as Astellas has legal authority to provide the data.

Researchers must submit a proposal to conduct a scientifically relevant analysis of the study data. The research proposal is reviewed by an Independent Research Panel. If the proposal is approved, access to the study data is provided in a secure data sharing environment after receipt of a signed Data Sharing Agreement.