Clinicopathological features of epiretinal membranes in eyes filled with silicone oil

Purpose: The aim of this case series was to clarify the clinicopathological features of epiretinal membranes (ERMs) that developed in eyes after silicone oil (SO) tamponade to treat rhegmatog-enous retinal detachments (RRDs). Patients and methods: In the Department of Ophthalmology, Saitama Medical Center, Jichi Medical University, patients with idiopathic ERMs (23 eyes) and ERMs in eyes filled with SO (SO ERMs) after vitreous surgery to treat RRDs (nine eyes) were enrolled from July 2012 to March 2014. ERM tissues obtained intraoperatively were examined histopathologically. Besides the main outcome measure of the pathological findings of the ERM tissues, other outcome measures included the preoperative findings on optical coherence tomography (OCT) images and the surgical findings. Results: Eight (89%) of nine eyes with SO ERMs had bilayered membranes composed of a firm layer on the retinal side with glial cells and extracellular matrix and a fragile sponge-like layer on the vitreous side. The sponge-like layer was composed of emulsified SO surrounded by macrophages. Quantitative analysis showed that the areas with cluster of differentiation 68 (CD68)-positive macrophages identified by immunohistochemistry in eyes with SO ERMs were significantly (P<0.001) larger than those in eyes with idiopathic ERMs. The findings on OCT images were consistent with the pathological features of the SO ERMs. Surgical removal of the SO ERMs was difficult because the sponge-like layer was fragile, and the underlying retina was also fragile due to inflammation. Conclusion: SO ERMs are bilayered membranes. Long-standing emulsified SO formed a sponge-like layer and SO (foreign body)-induced granulation and caused retinal inflammation in these eyes, making surgical removal difficult. A preoperative OCT examination is necessary to identify SO ERMs.