OCG/ICG imaging of choroidal neovascular membranes

Purpose: To evaluate to use of the combined OCT/SLO imager with ICG angiographic capability in the examination of patients with suspected choroidal neovascular membranes. Methods: The instrument consists of a scanning interferometer which produces paired C–scan (coronal) OCT and confocal SLO–type images. The optical source, a superluminescent diode (SLD) centered at 793 nm, is used for both OCT reflectometry and for the excitation of the ICG fluorescence. The system is also capable of providing OCT B–scans at selected points targetted from the ICG confocal image. 20 subjects with suspected CNV were studied pre and post injection of ICG dye into an antecubital vein. Special care was given to capture early transit phase images through the choroid and retina and very late phase images for evidence of delayed fluorescence accumulations (hot spots). OCT B–scan sequences were collected over areas observed to demonstrate increased fluorescence in the confocal channel. Results: Paired coronal OCT images demonstrated precise anatomic correlates to vascular features revealed in the ICG angiograms. The high resolution anatomy recorded in the OCT channel helped to provide a useful context to the often indistinct vascular outlines highlighted by the ICG fluoescense. Coronal OCT images were helpful in identifying the relative depth of particular vascular structures since they could be easily superimposed with precise registration and variable transparency. This facility proved especially valuable in the evaluation of occult lesions with late hot spots which were often evident when most adjacent vascular outlines were lost due to normal washout of ICG. Conclusions: The addition of ICG angiography to the OCT/SLO facilitates an integrated investigation of morphologic and angiographic features of choroidal neovascular lesions. The ability to accurately superimpose paired image channels which is made possible by the pixel–to–pixel correspondence, inherent in the system, may prove useful for isolating areas of late hyperfluorescense amenable to discrete laser treatment