Microcystic phenotypes of macular edema in silicone oil–filled eyes

Abstract Purpose The aim of this study was to investigate the prevalence and clinical characteristics of macular microcystic edema (MME) in eyes with silicone oil (SO) endotamponade, with particular emphasis on OCT-based phenotypes and their associated structural and functional features. Methods This retrospective cross-sectional study included eyes that underwent pars plana vitrectomy with SO for retinal detachment and had postoperative OCT imaging under SO endotamponade. Based on OCT findings, ME was classified into mixed phenotypes with both cystoid- and microcystic changes (CME/MME), and phenotypes with isolated MME. OCT biomarkers, layer-specific thickness measurements, and clinical variables were compared between phenotypes. Results Among 101 eyes with SO tamponade, ME was identified in 38 eyes (37.6%). Of these, 31 eyes (81.6%) were classified as mixed macular edema and 7 eyes (18.4%) as pure microcystic macular edema. Isolated MME was more frequent after routine SO removal (41.7%), whereas mixed CME/MME predominated in eyes with SO retained for more than 6 months (93.8%) or permanently (90.0%). Mixed macular edema was associated with greater inner retinal thickness, including higher average macular RNFL (55.3 vs. 32.6 μm, p = 0.002), macular GCL (36.2 vs. 28.1 μm, p = 0.04), and papillary RNFL thickness (109.6 vs. 84.1 μm, p = 0.001) compared with isolated MME. Conclusion ME under SO comprises two distinct OCT-defined phenotypes with different structural profiles. Pure MME and mixed edema represent heterogeneous retinal response patterns observed under SO tamponade, supporting OCT-based phenotyping to better contextualize SO-related retinal stress.