Supra-Choroidal Devices

Abstract

These devices are part of the MIGS techniques. The MIGS procedures (see Chap. 8) reduce the intraocular pressure (IOP) and improve the drainage or outflow of the aqueous humor (and to a lesser degree, reduce its production by the ciliary bodies). The MIGS that increase the drainage of the aqueous humor can influence several physiological pathways: some procedures improve the aqueous humor discharge into the Schlemm Canal (SC) by removing the resistance from the trabeculate (conventional discharge pathway), or by by-passing it. Other procedures improve the uveo-scleral drainage (non-conventional drainage pathway), creating a connection between the anterior chamber (AC) and the supra-choroidal space. The uveo-choroidal drainage system consists of the ciliary body, the suprachoroidal space, the choroid and the sclera. As mentioned previously, this pathway drains the aqueous humor from the AC into the supra-choroidal space. This occurs because of the natural pressure gradient between these two compartments and the high absorption capacity of the supra-choroidal space. The aqueous humor then drains from the supra-choroidal space through the blood vessels (scleral and choroido-capillary vessels), through the scleral pores, to then drain into the episcleral tissue. It is believed that in physiological terms, the therapeutic potential of the uveo-scleral drainage system is important: the uveo-scleral drainage is lower than the trabecular drainage, draining approximately between 5 and 44% of the total quantity of aqueous humor. Access to the supra-choroidal space through the creation of a cleft in the ciliary bodies, meaning a separation of the scleral spur from the ciliary bodies, is a pressure-lowering surgical procedure and is not a recent development. This type of surgery was not popular in the past because of the frequent and serious side-effects (severe hypotonia or acute hypertonia linked to the sudden closure of the cleft). To maintain long-term patency of the uveo-scleral pathway and to reduce the incidence of complications, over time, several different materials and substances have been suggested, but none has resulted in any significant clinical success. Recently, however, devices such as micro-stents and micro-shunts in new biocompatible materials have been presented:

• Gold Micro-Shunt (GMS, SOLX Corp, Waltham, MA)

• Cy-Pass Micro-Stent (Transcend medical, Menlo Park, CA)

• Aquashunt (Opko Health, Inc. Miami, FL