This study is designed to assess the safety and initial evidence of efficacy of the novel compound SOM-401 (K8), a derivative of a nucleoside reverse transcriptase inhibitor, in subjects with untreated, clinically significant, diabetic macular edema (DME).

Inclusion Criteria:

• 18 years or older
• BCVA of ≥ 24 and ≤ 73 letters (20/40 or worse but at least 20/320) by an ETDRS chart. BCVA of the non-study eye must be no worse than 20/400)
• Diagnosis of diabetes mellitus, type 1 or 2 with non-proliferative or non-high risk proliferative diabetic retinopathy.
• DME based on investigator's clinical evaluation and demonstrated on fundus photographs, fluorescein angiograms, and spectral domain-optical coherence tomography (SD-OCT)
• Mean foveal thickness of at least 300 µm by SD-OCT
• Ability and willingness to comply with the treatment and follow-up procedures
• Ability to understand and sign the informed consent form
• Intraocular pressure of ≤ 21 on 2 or less IOP lowering medications

Exclusion Criteria:

• Pregnant patients, currently lactating patients, or females of childbearing potential (unless using reliable contraception such as double barrier, surgical sterilization, oral contraceptives, intrauterine device (IUD), etc.)
• Allergy or hypersensitivity (known or suspected) to fluorescein or any component of the investigational product or delivery system
• Any ocular surgery in the study eye within 12 weeks of screening
• Any history of vitrectomy in the study eye
• Aphakia in the study eye
• Presence of severe foveal ischemia, defined as foveal avascular zone (FAZ) of >1.5 mm2 on OCT-Angiography
• Prior intraocular or periocular treatment for DME
• Macular laser for the treatment of diabetic macular edema within 12 weeks of screening
• Any change in systemic steroidal therapy within 3 months of screening
• Retinal or choroidal neovascularization due to ocular conditions other than diabetic retinopathy
• History or presence of viral disease of the cornea or conjunctiva
• History or presence of any disease or condition that in the investigator's opinion would preclude study treatment or follow-up or that in the opinion of the investigator would render them as unlikely to benefit from study treatment.
• Any lens or corneal opacity which impairs visualization of the posterior pole
• Participation in another clinical trial within 12 weeks before the screening visit or during the study
• Expectation that subject will be moving away from the area of the clinical treatment center without the ability to return for visits within the study period