Searching for clear episcleral fluid waves represented another clever approach to identifying AHO pathways by looking for negative signal in the form of disappearance of blood in surface epislceral veins . Conducted with the irrigation function on commercially available phacoemulsification units during cataract surgery, by delivering a clear perfusate into the anterior chamber, local AHO pathways were determined by observing the flushing out of episcleral veins. The advantage is that this technique would be very familiar and comfortable to ophthalmic surgeons. Disadvantages are the need to look for loss of signal as opposed to positive signal and the high/supra-physiologic pressures used. Clinically, when studied retrospectively, a statistically significant correlation was seen between patients with extrinsic episcleral fluid waves and better surgical success with trabecular bypass .