Intraoperative extraocular Indocyanine Green (IE-ICG) dye test: a new method of detecting a peeled internal limiting membrane

Abstract

AIMS: To develop an intraoperative, extraocular Indocyanine Green dye staining test (IE-ICG) for the differentiation of a peeled ILM from a thin epiretinal membrane, and to evaluate its efficacy. METHODS: This was a consecutive observational case and laboratory observational series. We performed ILM peeling in patients with an idiopathic macular hole (MH, n = 10) and diabetic macular oedema (DME, n = 10) without vital dye staining such as ICG or Trypan Blue. We also performed membrane peeling in patients with an idiopathic epiretinal membrane (ERM, n = 10). Then, the peeled membranes were stained with ICG (1.25 mg/ml) beyond the operation field and examined under a light microscope. After this examination, membranes were fixed with glutaraldehyde, and an electron microscope was used to confirm whether they were ILMs or thin ERM. The concordance rates between surgeon's intraoperative impression of membranes (SI), IE-ICG results (IT) and histological findings (HF) of peeled membranes were evaluated to reveal the efficacy of IE-ICG. RESULTS: The ILMs were homogenously stained with ICG dye (positive IE-ICG), and the ERMs were not stained at all by ICG dye (negative IE-ICG). The concordance rate between IT and HF was 100% in all three groups of patients. However, concordance rates between SI and IT were 100% in MH, 80% in DME and 50% in ERM, respectively. The surgeon's impression of the membrane is inaccurate, especially in patients with idiopathic epiretinal membrane. CONCLUSION: Considering the cost, difficulties of tissue preparation, and the time-consuming process of histological confirmation of an ILM, IE-ICG may be a useful alternative for the differentiation of a peeled ILM and a thin ERM.