Morphological and functional changes in recalcitrant diabetic macular oedema after intravitreal dexamethasone implant

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 centreinvolving DME associated with PDR, central macular thickness (CMT) =300 mm, 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 mm to 423±171 mm (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.