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Abstract #15981 Published in IGR 2-3
Uveoscleral Outflow: The other outflow pathway.
Weinreb BJournal of Glaucoma 2000; 9: 343-345
In this editorial the author describes his views on uveoscleral outflow. He was amazed that uveoscleral outflow seems to be no more than some 10 % of total outflow. How could drugs that affect uveoscleral outflow have such an effect on intraocular pressure? The name uveoscleral outflow comes from the studies by Anders Bill in 1965. He showed that tracers from the anterior chamber ended up in the uveal tract in the sclera. At normal intraocular pressure aqueous humor percolates through the extracellular spaces of the ciliary muscle, which are continuous with the anterior chamber and enters into the suprachoroidal space and anterior choroid. Fluid then leaks into the surrounding periocular tissues directly through the sclera or through the spaces surrounding penetrating vessels and nerves. This bulk flow is constant and largely independent of intra-ocular pressure in normal eyes. Uveoscleral outflow is present in most animal species but to a variable degree. In the human direct measurements of the uveoscleral outflow are difficult. Bill and co-authors studied outflow in eyes to be enucleated. In two untreated eyed the uveoscleral outflow counted for only 4 and 14% of total outflow. The author believes that it is because of this study that most people believe uveoscleral outflow contributes only minimally to total outflow in the human. Indirect measurements of the uveoscleral outflow also have their problems. Usually aqueous inflow and conventional outflow is estimated and the difference is unconventional outflow. Using such a method the contribution of uveoscleral outflow was estimated between 54 and 78% of total outflow. The author then continues by describing several drugs that affect uveoscleral outflow. This type of outflow can also be affected in disease such as uveitis. He makes a plea for further studies on uveoscleral outflow.
Classification:
2.6 Aqueous humor dynamics (Part of: 2 Anatomical structures in glaucoma)
