A Study to Test Whether BI 1815368 Helps People With an Eye Condition Called Diabetic Macular Edema

Inclusion criteria: * ≥18 years of age * Diagnosis of diabetes mellitus (DM) (type 1 or type 2), Haemoglobin A1C (HbA1c) \<12% treated with stable medication for at least 30 days prior to Day 1; no already-set plans for major changes in DM medication (e.g. start of new medication) at the time of screening and baseline * Centre-involved diabetic macular edema (CI-DME) confirmed on spectral domain optical coherence tomography (SD-OCT) with central subfield foveal thickness (CST) ≥320 µm in the study eye at screening * Best corrected visual acuity (BCVA) visual acuity Early Treatment Diabetic Retinopathy Study (ETDRS) letter score in the study eye between 24 and 78 (Snellen equivalent range 20/320 to 20/32) at screening Further inclusion criteria apply. Exclusion criteria: * Macular edema considered to be due to other causes than CI-DME in the study eye * Proliferative diabetic retinopathy or iris neovascularisation (including the anterior chamber angle) in the study eye * Intravitreal (IVT) anti-vascular endothelial growth factor (VEGF) treatment in the study eye is not allowed within 8 weeks prior to Day 1, except for faricimab or aflibercept 8 mg, for which a 16-week washout period prior to Day 1 is required. There is no limit on the total number of prior IVT antiVEGF injections, provided that the subject has demonstrated a response to prior antiVEGF treatment (at the investigator's discretion) and the anatomical integrity is confirmed by the central reading centre (CRC) at screening based on spectral domain optical coherence tomography (SD-OCT). * Any history of panretinal photocoagulation, vitreoretinal surgery, IVT or periocular corticosteroid treatment (within 12 months before Day 1), history of fluocinolone ophthalmic implant or dexamethasone IVT implant before Day 1, or topical steroid or nonsteroidal anti-inflammatory drug (NSAID) treatment (within 30 days before Day 1) * Prior macular laser photocoagulation performed more than 3 months prior to Day 1 is permitted if absence of scar-like changes within the 1-mm diameter region centred on the fovea is confirmed by the CRC at screening based on SD-OCT * Active ocular inflammation or any history of intraocular inflammation within 1 year * Aphakia or total absence of the posterior capsule; Yttrium aluminium garnet (YAG) laser capsulotomy in the study eye is permitted if more than 2 months prior to Day 1 Further exclusion criteria apply.