Occasionally, an additional dye called indocyanine green (or "ICG" for short) is used in combination with fluorescein. ICG dye, when used, is injected at the same time as fluorescein and is used to specifically highlight the blood vessels in the choroid. Among other things, ICG is useful in detecting certain conditions that can mimic AMD, such as central serous retinopathy. Of note is that ICG does contain a small amount of iodine, so we avoid its use in people that are sensitive to iodine. Other than that, the side effect profile for ICG is even milder than fluorescein, with the most common symptoms being darkening of the stools for a day or so.