Use of a multifocal electroretinogram to evaluate the therapeutic effect of a single intravitreal dexamethasone implant, Ozurdex®, for refractory diabetic macular oedema.

Aim: To evaluate the therapeutic effect of a single intravitreal dexamethasone implant (Ozurdex^®) in eyes with refractory diabetic macular oedema (DME) anatomically via optical coherence tomography (OCT) and functionally via best corrected visual acuity (BCVA) and multifocal electroretinography (mfERG).

Methods: This prospective interventional study included twenty eyes with refractory DME that were treated using six intravitreal injections of anti-vascular endothelial growth factor (VEGF). The central retinal thickness (CRT) was measured via OCT exceeding 300 μm. The eyes were treated with a single dexamethasone (DEX) implant four weeks after the last injection of anti-VEGF. The outcomes included changes in CRT, BCVA and p1 amplitude of ring 1 on mfERG and intraocular pressure (IOP) recorded before injection and two, four and six months after DEX injection.

Results: The study included fifteen males (75%) and five females (25%). The mean age was 62.83 ± 6.34 years, with the mean duration of diabetes was 16.7 ± 2.21 years. During the two-month follow-up, there were statistically significant reductions in CRT and logMAR BCVA as well as an increase in p1 of ring 1 on mfERG (P = 0.046, P < 0.001 and P < 0.001, respectively). At four months, these changes were not statistically significant (P = 0.99, P < 0.56&P < 0.58), whereas at six months, all the parameters nearly reached pre-DEX injection values (p = 0.93 P = 0.99 P = 0.81). The IOP values were not significantly increased at two, four or six months (p < 0.06, P = 0.35 and P = 1.0, respectively). There were significant negative correlations between the mfERG and OCT parameters before and six months after DEX injection (p = 0.000).

Conclusion: A single intravitreal injection of DEX in refractory DME patients induced significant anatomical and functional improvements, but these improvements only lasted for short periods of up to four months. This treatment exhibited an excellent safety profile. However, at six months, the therapeutic effect was null. The utility of mfERG as a sensitive biomarker of treatment efficacy was highlighted herein.