To understand the full AHO outflow pathways, one has to understand how it was discovered. Historically, one of the earliest clues for AHO came from Lauber’s dogs. Taking blood from ciliary veins, it was noted that the ciliary vein blood hematocrit was less than the peripheral vein hematocrit . This resulted in the hypothesis that the eye was diluting the blood by exuding some fluid into the systemic circulation leading to the discovery of the trabecular/conventional outflow pathway. While today we know that two AHO pathways exist (trabecular/conventional and uveoscleral/unconventional) [12–15], the purpose of this review is to focus on the conventional AHO route and the role of MIGS.