Indocyanine Green Angiography: A New Diagnostic Procedure
Spin-offs from NASA research and broadcasting camera technology have enabled high spectral and spatial resolution charge-coupled device (CCD) cameras to capture images in the visible and near infrared wavelength regions. These cameras, together with high speed computer processors and software image enhancement programs, enable us to obtain valuable information, which not only helps physicians diagnose but also treat more effectively the retinal diseases of our patients, often in the same day.
Standard fluorescein angiography has proven to be helpful in demonstrating and directing our laser treatments to well defined “classic” neovascular lesions secondary to age-related macular degeneration (ARMD). However, studies have shown that between 50 -85% of exudative “wet” ARMD lesions are of the “occult” variety, not amenable to laser treatment as per the Macular Photocoagulation Study guidelines.
Enter indocyanine green (ICG) angiography: Although this dye was in existence over a quarter century ago, it was not until high sensitivity solid state cameras became available that ICG fundoscopic imaging became a reality for the retina specialist. By imaging in the near-infrared spectrum we are now able to observe retinal pathology (disease) previously obscured by blood, lipid, and normal ocular pigment. Furthermore, by virtue of being highly protein bound, the ICG dye does not leak excessively from the choroidal vasculature as does standard fluorescein dye, allowing excellent demonstration of the vascular choroid, which lies between the retina and the sclera.
ICG technology, now available in our offices, has proven most useful in the detection and laser ablation of so called “hot spots,” indicating areas of active neovascularization in ARMD. With standard fluorescein angiography the standard protocol had been to treat everything with laser, including areas of the retina that might be uninvolved, because it was difficult to differentiate between the two. The ICG technology now allows us to look at a deeper section of the eye and see what is happening beneath the blood, so we can spare those unaffected areas.
ICG also gives insight into diseases that involve the layer deeper to the retina called the choroid. This is especially helpful for central serous retinopathy and certain inflammatory diseases known as uveitis.
Content written by Dr. David Tom, FACS