Background To evaluate the effects of dexamethasone implant in eyes affected by recalcitrant diabetic macular oedema (DME) associated with proliferative diabetic retinopathy (PDR).

Methods Thirteen consecutive patients with centre-involving DME associated with PDR, central macular thickness (CMT) ≥300 µm, previous therapy with panretinal photocoagulation, focal/grid laser treatment and anti-vascular endothelial growth factor injection were prospectively enrolled. A complete ophthalmological examination included: best-corrected visual acuity (BCVA) assessment, spectral-domain optical coherence tomography and fluorescein angiography. After the first dexamethasone implant, each patient was evaluated on a bi-monthly basis and re-treated according to persistence/recurrence of DME from the fourth month on. Primary outcome measures were the changes in mean BCVA and CMT at the 12-month examination. Secondary outcome measures included changes to the outer retinal layers.

Results BCVA improved from 0.99±0.31 LogMAR (logarithm of the minimum angle of resolution; Snellen Equivalent: 20/196) to 0.77±0.25 LogMAR (Snellen Equivalent: 20/117) (p<0.001) at the 12-month examination. CMT passed from baseline value 510±169 µm to 423±171 µm (p=0.018) at 12 months. The data showed a significant improvement in the integrity of the external limiting membrane (ELM, p=0.02), the ellipsoid zone (EZ, p=0.025) and retinal pigment epithelium (RPE, p=0.008), significantly correlated with the upturn in BCVA.

Conclusions Dexamethasone implant results in a recovery of morphology of the outer retinal layers even in patients displaying a compromised clinical situation. The qualitative status of the ELM and EZ might provide prognostic value for the final visual acuity and disease regression.