The specific aim of the study is to test the following hypothesis:

That switching between treatments from bevacizumab to Ozurdex or vice versa in eyes with diabetic macular oedema with no or incomplete response from one therapy is beneficial.

A Multicentre Clinical Trial of Switching Between Intravitreal Bevacizumab (Avastin®) and Intravitreal Dexamethasone (Ozurdex™) for Persistent Diabetic Macular Oedema (SwitchDMO)

Inclusion Criteria:

Eyes Previously Treated with bevacizumab:

1. Diabetic macular oedema affecting the fovea that has persisted despite ongoing, monthly intravitreal injections of bevacizumab over at least 6 months, the last being 2 to 3 months prior to the screening visit.

2. There must be an historical OCT available from 1-4 weeks after the last bevacizumab injection with retinal thickness > 300 microns in the central 1mm subfield on Spectral domain OCT to show the lack of complete response to bevacizumab.

3. At screening, the bevacizumab treated eye must have DMO with retinal thickness > 300 microns in the central 1mm subfield on Spectral domain OCT

   Eyes Previously Treated with dexamethasone:

4. Diabetic macular oedema affecting the fovea that has persisted despite two dexamethasone implants 5 or fewer months apart, the last being 5-8 months prior to the screening visit.

5. There must be an historical OCT available from 8-14 weeks after the last dexamethasone implant with retinal thickness > 300 microns in the central 1mm subfield on Spectral domain OCT to show the lack of complete response to the dexamethasone implant.

6. At screening, the dexamethasone treated eye must have DMO with retinal thickness > 300 microns in central 1mm subfield on Spectral domain OCT

7. Age >= 18 years

8. Diagnosis of diabetes mellitus

9. Best corrected visual acuity of 20-78 letters (approx 6/120 -6/7.5)

10. Previous macular laser treatment, or the investigator believes laser treatment is unlikely to be helpful

11. Intraocular pressure <22mmHg

12. Women of childbearing potential must have a negative urine pregnancy test at the screening visit and prior to treatment. A woman is considered of childbearing potential unless she is postmenopausal and without menses for 12 months or is surgically sterilised

13. Written informed consent has been obtained.

Exclusion Criteria:

• Treatment with intravitreal triamcinolone acetonide (IVTA) within the last 6 months or peribulbar TA within the last 3 months, or anti vascular endothelial growth factor (VEGF) drugs: ranibizumab and aflibercept, within the last 2 months.
• Cataract surgery within the last 3 months
• Retinal laser treatment within the last 3 months
• For eyes to be switched to Dexamethasone: Patient considered, at the judgement of the investigator, to be at-risk for syphilis, tuberculosis or other potentially infective chorioretinopathies. Patients considered at-risk may be assessed at the investigators discretion to reasonably exclude these conditions. Should these conditions be excluded, the patient may be considered for enrolment.