Sometimes it is useful to have a landmark to help measure the size of certain things in the posterior pole such as hemes, cotton wool spots, exudates, and particularly drusen when attempting to categorize AMD. Remember from the AREDS study that large drusen are those that are greater or equal to 125 microns. An easy way to gauge the size of drusen is to compare it the width of the central retinal vein, a classic landmark, which also happens to be roughly 125 microns.
