Chapter 6 Aqueous Humor Outflow Resistance

Unraveling the mystery of most diseases often begins with a simple comparison at the light microscopic level between the affected tissue in its normal and diseased state. The differences that are found serve to guide investigators to the ultimate cause of the disease. At this point, the differences found between the trabecular meshworks of age-matched normals and glaucomatous human eyes are very few-regardless of the method of analysis. This provides ample room for further investigation but is simultaneously a great source of frustration for both the basic scientist and the clinician. Much as glaucoma is a disease of increased resistance, the disease process itself remains resistant to giving up its secrets. Outflow resistance is the inverse of facility of outflow. Although our search for the source of outflow resistance in both the normal and glaucomatous eye must continue, the fluid mechanics of the process can still be simplified to their clinical essence using the formula developed by Goldmann: F=C_tm (P_i-P_e) + F_u, where F equals aqueous flow in μl/min; P_i and P_e represent intraocular and episcleral venous pressure, respectively, in mm Hg; F_u represents the component of outflow traveling the unconventional route; and the value C_tm remains the measurable but elusive facility of outflow-the mirror of outflow resistance.