Development of novel glaucoma drainage implant for efficient regulation of intraocular pressure

Abstract

 

Purpose

 

To present a novel glaucoma drainage implant (GDI) and to evaluate its pressure-flow characteristics both in vitro and in rabbit eyes.

 

Methods

 

Two types of novel GDI made of polydimethylsiloxane (PDMS) were designed, a curved type and a flat type, both for a one-way check valve. The valve opens an inner flip-flop-mode membrane when the aqueous flow in a shunt channel reaches the cracking pressure. The flow resistances of the GDIs according to various flow rates were measured in vitro. The novel GDIs and Ahmed™ glaucoma valve (AGV) (model FP-8) were perfused with balanced salt solution (BSS) at rates of 2 and 4 µl/min for 20 minutes, and the resultant pressure in the shunt channel was monitored by a pressure sensor both in vitro and in rabbit eyes. The rabbit eyes subsequently were examined by microscopy, tonometry (TonoPen), and ultrasound biomicroscopy (UBM) up to twelve weeks, and were then enucleated for a histological examination.

 

Results

 

In vitro, the flow resistances of the novel GDIs were lower than that of the AGV, whereas the AGV had the lowest starting pressure at a flow rate of l µl/min. Six weeks after implantation in the rabbit eyes, the shunt channel pressures in the novel GDIs were lower than that in the AGV. At twelve weeks post-implantation, the shunt channel pressures in the novel GDIs were similar to that in the AGV (Figure 1). There was no hypotensive phase in the novel GDIs, unlike AGV, which showed an early hypotensive phase. The microscopic in vivo evaluations performed up to twelve weeks post-implantation showed favorable biocompatibility and complete patency for both types of the novel GDIs. The UBM showed a low and diffuse bleb for the curved type but not for the flat type or AGV. Histologically, the curved type novel GDI showed, relative to the flat type novel GDI and AGV, a thin capsule with little connective tissue.

 

Conclusions

 

The novel GDIs, especially that with the curved plate (curved type), showed a stable IOP lowering effect compared with the AGV.

 

 

Figure 1) Pressure versus flow curves in rabbit eyes A. Six weeks post-implantation at perfusion rate of 2 µl / min in rabbit eyes B. Six weeks post-implantation at perfusion rate of 4 µl / min in rabbit eyes. C. Twelve weeks post-implantation at perfusion rate of 2 µl / min in rabbit eyes. D. Twelve weeks post-implantation at perfusion rate of 4 µl / min in rabbit eyes.

 

Keywords: 568 intraocular pressure