Purchase this article with an account.
EUN KYOUNG KIM, Edward Chu, Aleksandr Yelenskiy, Jose Gonzalez, James Tan; Artificial Simulation of Conventional Aqueous Humor Outflow Dynamics. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3561.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To construct and test an artificial system to simulate, measure and better understand conventional outflow dynamics.
We constructed an artificial perfusion model with the following key components: 1) 50ul glass syringe on a microsyringe pump (representing aqueous inflow), 2) modified small caliber 35G needle to provide resistance (trabecular meshwork (TM) resistor), 3) 1-way valve (Schlemm’s canal inner wall endothelium (SCIW) barrier), and 4) distal fluid column (episcleral venous pressure (EVP)), all connected in series via rigid tubing with 3 intervening pressure transducers (PT). PT#1 (representing intraocular pressure (IOP)) was connected between pump and needle, PT#2 (tissue pressure) between needle and valve, PT#3 (EVP) between valve and column. Needle resistance, pump flow rate calibration and valve cracking (opening) pressure were characterized separately. A voltage feedback loop between the pump and PT#1 was set up via an analogue voltage controller that allowed pump flow rate to vary automatically to maintain a pre-set constant perfusion pressure. Flow rate and all pressure data were simultaneously sampled at millisecond intervals and viewed in real time in LabChart software.
Adjusted for valve cracking pressure, consistent pumping did not start until the pressure in PT#1 exceeded PT#3 (PT#1>PT#3), indicating no measureable outflow at IOP below EVP. For PT#1<PT#3, PT#1 equaled PT#2, but once PT#1>PT#3, PT#1 gradually exceeded PT#2 with the differential between PT#1 and PT#2 increasing with pressure, consistent with the effect of needle (TM) resistance. Once outflow was established when PT#1 (IOP)>PT#3 (EVP), increasing fluid column height so that PT#3>PT#1 caused the pump to stop, reflecting outflow cessation. In the absence of a valve (SCIW), a pressure differential could not be maintained between PT#1 (IOP) and PT#3 (EVP). In the absence of needle (TM) resistance, unrestricted pumping (outflow) occurred once PT#1 (IOP)>PT#3 (EVP).
The artificial model simulated physiological characteristics that may be predicted of the conventional outflow pathway. Physical features of system components could be altered, and effects of this observed and quantified directly. This model provides a platform for simulating and understanding physiological and pathological aspects of aqueous dynamics and improving analytical approaches for live animal studies.
This PDF is available to Subscribers Only