Efficacy of Subthreshold Photocoagulation for Persistent Diabetic Macular Edema After Internal Limiting Membrane Peeling: A Retrospective Comparative Study

Background Subthreshold photocoagulation is one of the therapeutic options for treating diabetic macular edema, and have characteristic advantages, which are the lack of chorioretinal damage and the repeatability of the treatment. However, the effect of subthreshold photocoagulation is thought to be minimal among these options. In this study, we retrospectively examined the efficacy of repeated subthreshold photocoagulation for persistent diabetic macular edema after vitrectomy with peeling of the internal limiting membrane. Methods We enrolled ten consecutive eyes of eight patients who underwent monthly Endpoint Management™ (EpM) six times for diabetic macular edema that persisted for more than 3 months after vitrectomy with internal limiting membrane peeling for epiretinal membrane, and classified according to the interval between vitrectomy and initial EpM (Group A: within 6 months, Group B: beyond 6 months). Two type of retinal thickness (central macular thickness and macular thickness within 3mm diameter of the fovea) were measured monthly using optical coherence tomography. Results Mean intervals between vitrectomy and initial EpM were 4.0 ± 1.2 months (range 3–6 months) in Group A (six eyes of five patients) and 17.3 ± 7.5 months (range 10–27 months) in Group B (four eyes of four patients). No other treatments were performed between vitrectomy and initial EpM in Group A, while triamcinolone acetonide injection in the sub-Tenon’s capsule was performed in two eyes in Group B (one eye was injected thrice, the other eye received a single injection). Improvement rates of mean central macular thickness after 6 months were 18.2% in all eyes, 10.8% in Group A, and 28.7% in Group B, and improvement rates of mean macular thickness within 3mm diameter of the fovea after 6 months were 8.5% in all eyes, 4.1% in Group A, and 15.3% in Group B. Conclusions Monthly EpM treatment was efficacious against persistent diabetic macular edema after internal limiting membrane peeling. In particular, the efficacy was greater in eyes in which the initial EpM was performed more than 6 months after vitrectomy. Furthermore, residual efficacy of triamcinolone acetonide, which was injected at the end of vitrectomy, might have contributed to the results.