This study is open to adults 18 and older with an eye condition called diabetic macular edema. People are required to have a specific type of diabetic macular edema called centre-involved diabetic macular edema (CI-DME) to take part. The purpose of this study is to find out whether a medicine called BI 1815368 improves sight in people with CI-DME and to find the most suitable dose.

This study has 2 parts. In the first part, participants are put into 2 groups of equal size randomly, which means by chance. One group takes BI 1815368 tablets and the other group takes placebo tablets. Placebo tablets look like BI 1815368 tablets but do not contain any medicine. In the second part, participants are put into 4 groups of equal size randomly. 3 groups take different daily doses of the study medicine, BI 1815368, while 1 group takes placebo. All participants take tablets twice a day for about 11 months.

Participants are in the study for about 1 year. During this time, they visit the study site 16 times. At visits, doctors check the participant's vision and collect information on any health problems. They take detailed pictures of the eye. The changes over time are compared between the groups to see if the treatment works.

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
• Any intravitreal (IVT) anti-vascular endothelial growth factor (VEGF) treatment within 4 months before Day 1 (other than faricimab or aflibercept 8mg), and within 6 months before Day 1 for faricimab or aflibercept 8 mg, and/or more than 4 prior IVT injections with anti-VEGF treatment in total in the study eye
• Any history of panretinal photocoagulation, macular laser 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 NSAID treatment (within 30 days before Day 1)
• Active ocular inflammation of 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.

Once the criteria in section "Time Frame" are fulfilled, researchers can use the following link https://www.clinicalstudies.boehringer-ingelheim.com/msw/datasharing to request access to the clinical study documents regarding this study, and upon a signed "Document Sharing Agreement".

Furthermore, researchers can request access to the clinical study data, for this and other listed studies, after the submission of a research proposal and according to the terms outlined in the website.

One year after the approval has been granted by major Regulatory Authorities and after the primary manuscript has been accepted for publication, or after termination of the development program.

For study documents - upon signing of a "Document Sharing Agreement". For study data - 1. after the submission and approval of the research proposal (checks will be performed by the sponsor and/or the independent review panel, including checking that the planned analysis does not compete with sponsor's publication plan); 2. and upon signing of a legal agreement.