Fig. 11.1
Gold Micro-Shunt. The GMS is a device consisting of two wings that are fused together; it is rectangular and is equipped with a rounded proximal edge that enters the AC. The distal edge is designed with small fin-shaped wings that helps to anchoring the device in the suprachoroidal space. The drawing illustrates the internal section of the GMS; there are canals and tubules that facilitate the flow of aqueous humor from the AC to the suprachoroidal space. The shunt is 5.2 mm long, 3.2 mm wide and 44 μm thick. It has 19 canals or tubules: 9 of these are open with a lumen 24 μm wide and height 50 μm. On the proximal edge, there are 60 small holes (of diameter 100 μm) and a hole of 300 μm that allows the aqueous humor to drain into the shunt. The distal part has a grid consisting of 117 holes (of diameter 110 μm) that allow the liquid to drain from the shunt. Finally, there are other canals (12 anterior and 10 posterior) on the sides that also allow the outflow of aqueous humor
Surgical Technique
The series of drawings that follow illustrate the various surgical steps.
Fig. 11.2
Conjunctival Flap and Scleral Incision . After having created the conjunctival fornix based flap, the surgeon creates a scleral incision that is 4 mm long; it extends for approximately 90% of the scleral depth and is positioned 2–3 mm from the limbus
Fig. 11.3
Scleral Tunnel . A scleral tunnel is created, using trapezoidal or crescent knives. The surgeon creates a scleral tunnel that is directed anteriorly towards the cornea. The AC depth can be maintained with VES or with an AC maintainer
Fig. 11.4
An implant with a dedicated injector. A dedicated re-usable, sterilizable injector is available for inserting and positioning the implant. The injector is inserted in the scleral tunnel; the surgeon proceeds in an anterior direction to allow the distal portion enters the AC
Fig. 11.5
(a, b) Removal of the injector. At this point, the injector is withdrawn (a); part of the device remains inside the AC and part inside the scleral tunnel (b)
Fig. 11.6
Positioning the distal portion of the device. The device is now mobilized anteriorly towards the AC (see the red arrow), using a standard hook inserted through one of the numerous holes. The distal portion of the device is introduced into the AC: it has a concave shape designed to minimize any possible contact with the iris or with the corneal endothelium. Only 1–1.5 mm of the device should be visible in the AC
Fig. 11.7
Positioning the proximal portion of the device. The proximal portion of the device is positioned in the suprachoroidal space, again using a hook (see the red arrow), so that all the posterior drainage openings are covered by the posterior scleral slit. The correct position of the implant can be controlled by intraoperative gonioscopy
Fig. 11.8
Correct final position of the Gold Shunt (side view). The distal portion of the device enters the AC for 1–1.5 mm, while the posterior portion is positioned in the supra-choroidal space
Results
This procedure is indicated for primary or secondary open-angle glaucoma. Only a few clinical studies have been published in the literature and they report that the IOP reduction is comparable to those provided by other MIGS. Similarly, the rate of complications, such as transitory hypoema, is low and mild. Sometimes, thin membranes may form on the surface of the implant. They may occlude the anterior or posterior holes and lead to a rise in IOP.
The CyPass Micro-Stent
Introduction
The CyPass Micro-Stent is a minimally invasive supra-choroidal device implanted using an ab-interno approach (that will avoid manipulation of the conjunctiva and the sclera). It has been produced in a biocompatible and not biodegradable material, similar to the polyamide used to create the loops of the IOL.
Fig. 11.9
The CyPass Micro-Stent. The device consists of a tube, 6.35 mm long, with an external diameter of approximately 0.5 mm and a lumen of 300 μm. There are fenestrations along the length of the device for the drainage of the aqueous humor
Surgical Technique
The implantation technique is relatively simple, and associated with a fairly short learning curve, even for young and less experienced surgeons. The device can be inserted through an incision in clear cornea; this can be an isolated procedure or it can be performed in combination with phacoemulsification. For this type of procedure, the surgeon sits in a specific position, as described in Chap. 7 for goniotomy: he sits on the side opposite the portion of the angle he wishes to operate on. The patient’s head is rotated slightly on the opposite side with respect to the surgeon. The operating microscope is tilted 30°–45° to consent excellent visualization of the angle.
