The meaning of any tracer study in any system is only as good as how close the tracer models the native substance of interest. The use of multiple tracers above with similar results of segmental AHO patterns in multiple species has been very reassuring. For AHO, aqueous humor is actually made up of many components . Predominately, aqueous humor is composed of water (molecular weight=18 g/mol). Small components such as ions are present. Other, less abundant components include small molecules (eg vitamin C…), to macromolecules (protein/DNA/RNA), to larger structures and cellular components. In a way, testing AHO with multiple tracers of different characteristics is the best way to model AHO. Larger tracers such microspheres [47–52] may reflect the larger component of aqueous. Given ICG’s propensity for protein binding, ICG aqueous angiography (Saraswathy S, et al. IOVS 2015; 56: ARVO Abstract 247) may mimic flow of proteins. Smaller tracers such as fluorescein better models small molecules and water . Putting these together a more comprehensive and realistic picture of aqueous outflow can be presented.