Abstract
Abstract: :
Purpose: To demonstrate pump-like outflow system behavior through clinical evidence of pulsatile aqueous flow from the anterior chamber into Schlemm's canal and pulsatile aqueous flow from Schlemm's canal into the aqueous veins in synchrony with the cardiac pulse. Methods: Clinical videographic observations document pulsatile aqueous flow into SC during gonioscopy and pulsatile aqueous flow from SC to the aqueous veins during slitlamp examination using microscopes capable of 80-power magnification. Clinical observations are correlated with observations from the laboratory including the dissecting microscope, light microscopy, scanning electron microscopy, transmission electron microscopy and tracer studies. Results: Pulsatile flow of aqueous from the AC into SC is visible as a white area against a background of blood intentionally refluxed into the canal. Aqueous flow pulsations originate in a white funnel-shaped region that then attains a cylindrical configuration as it runs circumferentially in SC. The funnel shape collapses as the white cylindrical region expands. Collapse of the cylindrical region follows accompanied by discharge of a clear bolus of aqueous into SC at the distal end of the cylinder. The rhythmically recurring aqueous discharge sequence is synchronous with the cardiac pulse. Characteristics of the pulse wave of aqueous entering the episcleral veins in synchrony with the cardiac pulse indicates the pulsations arise from SC rather than from retrograde venous pulsations. Clinical observation of pulsatile pump-like aqueous flow is in accord with laboratory studies. Such studies document pressure-dependent excursions of the highly compliant trabecular meshwork. Anatomic studies also document a system of valve-like structures arising from Schlemm's canal endothelium to initially develop a funnel-shape. The funnel narrows to develop a cylindrical configuration as the structures course circumferentially in SC. Anatomic studies show that the valve-like structures undergo pressure-dependent changes in configuration and tracer studies demonstrate that the structures have a lumen capable of carrying both aqueous and red blood cells. Conclusions: This clinical report demonstrates pump-like pulsatile aqueous flow in response to IOP gradients generated by the cardiac pulse. Clinical evidence of pulsatile aqueous flow into and out of SC is in accord with anatomic features and dynamic pressure-dependent structural responses demonstrated in the laboratory.
Keywords: clinical (human) or epidemiologic studies: sys • outflow: trabecular meshwork • trabecular meshwork