Indocyanine green concentrations used in chromovitrectomy cause a reversible functional alteration in the outer blood-retinal barrier

Purpose To assess tight junction integrity in cultured human foetal retinal pigment epithelium (RPE) after exposure to clinically relevant indocyanine green (ICG) concentrations. Methods Human foetal RPE was cultured with the Hu & Bok method. The apical compartments of well-differentiated cultures were exposed to 0.125, 0.05 and 0.025mg/ml ICG with or without 10-min illumination. Vehicle and trypsin/EDTA or EDTA alone served as controls. Three minutes was chosen to mimic surgical exposure time, while 3h was used for toxicity assays, with subsequent wash out. Cell-cell junctions were studied before and after exposure by phase contrast microscopy and immunofluorescence (ZO-1). Blood-retinal barrier function was measured through transepithelial electrical resistance (TER). Results At 6-8weeks postconfluence, RPE had grown into pigmented hexagonal monolayers with stable TER (435-1227 omega*cm(2)). After 3min ICG exposure, cell morphology remained unchanged, with patchy cell-cell dissociation in positive controls. A continuous ZO-1 signal was detected in ICG groups, whereas trypsin controls showed patchy loss of the tight junction stain. TER had dropped at 1.5h after 3min exposure to 22.8 +/- 3.1%, compared with 10.2 +/- 3.9% in positive controls. Surgical light illumination did not affect TER. After 3h exposure to 0.05mg/ml ICG, TER decreased to 58.1 +/- 8.3%, while vehicle controls maintained similar levels as prior to exposure (92.7 +/- 2.4%). TER recovered in all ICG groups to prior levels within 3days. Conclusion Indocyanine green (ICG) exposure induced a transient decrease in transepithelial electrical resistance, despite unaltered tight junction structure.