Chapter 7 Aqueous Humor Dynamics I. Measurement Methods and Animal Studies

The use of animal models to investigate the circulation of aqueous humor in normal ocular health and chronic ocular diseases that disturb the IOP requires an appreciation for the diversity among species in the anatomical and physiological differences in the iridocorneal angle. Extrapolating animal findings to human disease requires discretion. Methods have been developed recently to measure the components of aqueous humor dynamics in the tiny murine eye, making the mouse the preferred model for genetic studies of glaucoma. Some breeds of dog suffer from spontaneous glaucoma that provides clues to the pathogenesis of glaucoma in humans. Study of these breeds has contributed to improved treatments for human as well as canine glaucoma. The monkey remains the most valuable animal model for understanding aqueous humor dynamics in human glaucoma because of its anatomical and physiological similarities to humans. There are a myriad of methods available to assess the four main parameters of aqueous humor dynamics, aqueous flow, outflow facility, uveoscleral outflow, and episcleral venous pressure. The most accurate methods are invasive and often terminal. Methods designed for one species may not be easily adaptable for another. The noninvasive methods are indirect, highly variable, and fraught with many limitations and assumptions. Nevertheless, these methods remain useful in clinical research. Imaging techniques are evolving rapidly and may soon become sufficiently sensitive to allow simultaneous visualization and quantitation of ocular hydrodynamics in a direct noninvasive manner.