Abstract
Abstract: :
Purpose: The Ex–PRESS (Optonol, Israel) is a miniature unvalved, flow–restricting glaucoma implant. The device is a 3mm–long tube, with a 400µm external diameter that is made of implantable stainless steel approved for medical and ophthalmic applications. An indwelled unit inside the cannula serves to restrict flow. The purpose of this study was to test the pressure/flow characteristics of this device at physiologic flow rate (2µL/min), under controlled in–vitro conditions. Methods: All testing were done with devices in which the lumen was restricted to different extends (19±16µm, 26±14µm, 45±16µm, and 203±18µm), designated as R20, R30, R50, and R200, respectively. The following tests have been conducted: Gravity flow test – to calculate the theoretical resistance to flow and Constant flow test – to evaluate the pressure/flow characteristics of the device under constant flow rate. Data was compared to expected values calculated using the Possilles formula. Results: The mean values of pressure gradient measured at a physiologic flow rate were 1.05±0.16, 0.69±0.12, 0.18±0.02, and 0.014±0.001 mmHg, for the R20, R30, R50, and R200 devices, respectively. The correspondence resistance values are presented below: Conslusion: The study demonstrates that it is possible to control the dimensions of a manufactured lumen in a miniature glaucoma implant accurately enough to provide consistent restriction to flow. It was shown that the measured resistance to flow correlated with the inner diameter of the device and corresponded to the theoretical values that were obtained by the gravity flow tests. In this respect, the Ex–PRESS is an implant with an effective reproducible resistance to flow, which meets a prerequisite to gain acceptance as an effective glaucoma drainage device.
Keywords: clinical laboratory testing • aqueous • intraocular pressure