I'm studying for the CRA exam and am finding myself confused by some of the wording around the red filter used for ICG. On one page of the book, it talks about using a 640 nm red filter to image the choroid just using fundus photography (no dye). And then later on, when you get to the ICG section of the book, it mentions 800-810 nm absorption rates of the dye, with it emitting at around 835 nm. Are these supposedly two different filters? Can ICG just be used with a wide spectrum of red light? I could really use a nice rundown of the red filters used for both fundus photography as well as ICG angiograms. 

Thank you!