Today, understanding AHO structure is more sophisticated than traditional casting methods. Initially, pathological/histological and electron microscopic methods were used . TM, SC, and distal outflow structures were observed. Sampling of these structures across the eye revealed an overall impression of non-360 degrees uniform luminal sizes and presence . Electron microscopic results implied the presence of “plaque” material in glaucomatous eyes not found in normal eyes that may have been related to increased outflow resistance. Limitations of these approaches were associated with variability in tissue procurement, possible fixation artifacts, and sample preparations differences .