Prognostic role of optical coherence tomography after switch to dexamethasone in diabetic macular edema

Aims To analyze the visual outcome after early switch to dexamethasone (DEX) in eyes with diabetic macular edema previously treated with ranibizumab (RNB), based on structural spectral-domain optical coherence tomography (SD-OCT) features. Methods Retrospective study of data from 28 eyes which underwent a loading dose of three monthly RNB injections and were then shifted to DEX implant injection. SD-OCT analysis was performed before switch to DEX (week 12, 12W) according to the presence of integrity of ellipsoid zone (EZ) and external limiting membrane (ELM), disorganization of retinal inner layers (DRIL), and quantity of hyper-reflective spots (HRS). Best-corrected visual acuity (BCVA) changes at different time points after DEX (month 1, 1M; 4 months, 4M; and 12 months, 12M) were compared among groups. Results Significantly better BCVA was achieved at 1M in eyes with intact EZ (84.2 +/- 12.3 letters; p = 0.04), with intact ELM (83.2 +/- 11.5 letters; p < 0.01), and with fewer HRS (84.6 +/- 12.5 letters; p = 0.03). However, the greatest percentage visual increase was achieved in eyes with disrupted EZ (+ 11.4%; p < 0.01), with disrupted ELM (+ 17.2%; p < 0.01), without DRIL (+ 12.5%; p < 0.01), and with more HRS (+ 14.3%; p = 0.04). After 12 months, a significant BCVA gain was observed only in eyes with intact retinal inner layers (+ 14.2%; p = 0.03). Conclusions Greater percentage BCVA improvement at 1M after switch to DEX was associated with EZ disruption, ELM disruption, intact retinal inner layers, and higher quantity of HRS. A switch to DEX therapy would be useful in patients with these SD-OCT features.