This pilot prospective, interventional, longitudinal study, aims to evaluate the potential benefits of the probiotic supplement Lactobacillus plantarum 299v in patients with diabetic macular edema (DME).

The study seeks to address the following questions:

1. Does central macular thickness on optical coherence tomography decrease after 4 months of supplementation?
2. Is visual acuity improved at 1, 2, 3, and 4 months following initiation of supplementation?
3. Is the number of anti-VEGF injections reduced following initiation of supplementation?

Outcomes will be compared to a control group, using historic retrospective data.

Participants will take Lactobacillus plantarum 299v orally twice daily for four months.

Study Design: Prospective open label longitudinal interventional study with oral probiotic supplement Lactobacillus plantarum.

Inclusion criteria: Age of at least 18 years, presence of DME at the current clinical visit

Exclusion criteria: Patients with contraindication to probiotic supplement (e.g. prior allergy or GI intolerance and any type of immunocompromised diseases).

Eligible individuals (patients at least 18 years old with diabetic macular

Participants: Patients with DME that belong in the following two groups:

• Group A: 12 Patients with mild DME and good visual acuity (<= 20/30) similar to DRCR network protocol V that do not need anti-VEGF injections as per standard clinical care.
• Group B: 12 Patients with DME that need anti-VEGF injections as per standard clinical care.

Intervention: Oral probiotic supplement L. plantarum 299v twice daily for 4 months for both groups.

Study outcomes:

• OCT with central macular thickness (CMT) at 1, 2, 3, 4-months follow-up.
• Visual Acuity at 1, 2, 3, 4-months follow-up.
• Number of anti VEGF injections.

In group A, the percentage of patients with a stability or improvement in DME as determined by a stability (+/- 9% of OCT CMT) or a reduction of DME (>= 30 microns or >= 10% decrease of CMT) from baseline will be measured. Secondary endpoints will be visual acuity and need for injection initiation during the 4 months.

In group B, the same outcomes as in group A will be measured. Furthermore, the number of injections group A over the course of 4 months will be evaluated.

Data from both groups will be compared to historical data available at the study site.

Inclusion Criteria:

• Age of at least 18 years, presence of DME at the current clinical visit

Exclusion Criteria:

• Patients with contraindication to probiotic supplement (e.g. prior allergy or GI intolerance and any type of immunocompromised diseases).

Individual participant data will not be shared. Although data would be de-identified, the small sample size and single-center design increase the risk of re-identification. Therefore, results will be reported in aggregate only. There are no current plans for external sharing of IPD.