The purpose of the study is to compare the effect of intravitreal injections of ranibizumab and aflibercept on systemic VEGF levels in DME patients in a detailed time course.

The purpose of the study is to compare the effect of monthly intravitreal injections of 0.5 mg ranibizumab and 2.0 mg aflibercept on systemic VEGF levels in patients with visual impairment due to DME over a 24 week period. In addition, the study will also assess the effect on systemic VEGF-A levels when patients are switched from aflibercept to ranibizumab.

Inclusion Criteria:

• Type 1 or Type 2 diabetes mellitus
• Visual impairment due to DME
• BCVA of 78 to 24 (20/32-20/320) ETDRS letters

Exclusion Criteria:

• Stroke or myocardial infarction less than 3 months prior to screening.
• Presence of uncontrolled systolic blood pressure or diastolic blood pressure
• Renal failure requiring dialysis or renal transplant or renal insufficiency
• Untreated diabetes mellitus
• Use of any systemic anti-VEGF drugs within 6 months prior to screening.
• Use of systemic or inhaled corticosteroids for at least 30 consecutive days within 3 months prior to screening.
• Women who are pregnant or breast feeding or who are menstruating and capable of becoming pregnant* and not practicing a medically approved method of contraception

For either eye:

• Any active periocular or ocular infection or inflammation
• Uncontrolled glaucoma
• Neovascularization of the iris or neovascular glaucoma
• History of treatment with any anti-angiogenic drugs

For study eye:

• Atrophy or fibrosis involving the center of the fovea at the time of screening or baseline.
• Cataract (if causing significant visual impairment), planned cataract surgery during the study period, vitrectomy, aphakia, glaucoma surgery, severe vitreous hemorrhage, rhegm
• Irreversible structural damage within 0.5 disc diameter of the center of the macula
• Panretinal laser photocoagulation within 6 months prior to randomization.
• Focal/grid laser photocoagulation within 3 months prior to randomization.
• Any intraocular procedure (including cataract surgery, Yttrium-Aluminum-Garnet capsulotomy) within 3 months prior to baseline or anticipated within the next 6 months following
• Topical ocular corticosteroids administered for at least 30 consecutive days within 3 months prior to screening.
• Application of intravitreal corticosteroids in vitreous within 6 months prior to screening. Prior application of fluocinolonacetonid releasing implant in vitreous within 36 months prior to screening.

For fellow eye

- Retinal or choroidal neovascularization or macula edema of any cause Other protocol-defined inclusion/exclusion criteria may apply.