Minimally Invasive Mini-Glaucoma Shunt Implantation
Before beginning the surgical dissection, the location for the shunt placement should be determined. A region with minimal episcleral vascularization with small caliber vessels should be chosen and areas which have undergone previous scleral incisions for cataract surgery should be avoided. The superior bulbar conjunctival vessels can be constricted with a circular Merocel sponge soaked in phenylephrine 2.5% and placed for 10 to 15 minutes. In addition, a superior subconjunctival injection of xylocaine 1% with epinephrine helps constrict the episcleral vessels and reduce the severity of subconjunctival bleeding when the scleral dissection is opened into the subconjunctival space.
The first step of the procedure involves a clear corneal incision placed just anterior to the conjunctival insertion. This incision can be created with a diamond or steel-step knife and should be approximately 350 μm in depth and 4 mm in length (Fig. 1). A scleral pocket is then dissected posteriorly with a beveled crescent blade for approximately 3 mm ([Fig. 2). The scleral pocket is opened into the subconjunctival space with either the crescent knife or a sharp-tipped diamond or metal keratome (Fig. 3). Most recently, a Sharpoint 1.1 mm paracentesis knife (Model 78–2010) has been found to facilitate entry into the subconjunctival space (DAC). A 90-degree bend is made at the tip of the knife and after passing the knife into the sclera pocket with the bent tip parallel to the plane of dissection, the tip is rotated into a vertical orientation to perforate the roof of the pocket (Fig. 4). The tip is then used to slice a complete full-length opening into the subconjunctival space.
(Enlarge Image)
Figure 1.
A 4-mm long grooved incision is made with a 350 mm step-knife just anterior to the conjunctival insertion.
(Enlarge Image)
Figure 2.
A crescent knife is used to dissect a scleral pocket 3mm posterior to the grooved incision.
(Enlarge Image)
Figure 3.
The scleral pocket is opened into the subconjunctival space with a sharp-tipped keratome creating a scleral tunnel.
(Enlarge Image)
Figure 4.
A 1.1-mm paracentesis knife with the tip bent 90 degrees is used to open the sclera pocket into the subconjunctival space.
After completion of the scleral tunnel, the wound is then opened by placing a small skin hook or Kuglin hook under the roof of the scleral tunnel and a Sinskey hook within the corneal stroma of the anterior aspect of the grooved clear corneal incision. An assistant would hold the Sinskey hook while the surgeon holds the skin hook in their nondominant hand. With gentle opposing traction, the Sinskey hook will pull the external anatomic structures overlying the trabecular meshwork anteriorly as the skin hook retracts the roof of the scleral tunnel, thus exposing the site for the mini-shunt placement (Fig. 5). A 27-G needle with a bent tip is then inserted into the anterior chamber, just anterior to the posterior aspect of the blue zone that overlies the region of the trabecular meshwork (Fig. 6). The needle tip should be bent and inserted so that the resulting microincision is parallel to the plane of the iris. The Ex-PRESS shunt is then inserted into the incision, initially rotated 90 degrees from its ultimate final position (Fig. 7). Once it is seated with the external flange against the sclera, it is rotated 90 degrees into the proper orientation and the injector is squeezed to release the shunt. Although it is not possible to orient the shunt insertion in the iris plane because of the current limitations in the injector design and the limited anatomic exposure; a properly constructed perforating microincision and the overlying scleral tunnel roof apposed against the shunt's external flange will ultimately orient the shunt tip parallel with the iris.
(Enlarge Image)
Figure 5.
A skin hook retracts the roof of the scleral tunnel while a Sinskey hook pulls the external anatomic structures overlying the trabecular meshwork anteriorly, exposing the site for minishunt placement.
(Enlarge Image)
Figure 6.
A 27-G needle with a bent tip is inserted into the anterior chamber parallel to the iris and anterior to the posterior aspect of the blue zone.
(Enlarge Image)
Figure 7.
The Ex-PRESS shunt is inserted into the incision, initially rotated 90 degrees from its ultimate final position.
Once the shunt is in position, the hooks are removed and a single tangential 10–0 nylon suture is placed at the limbus to close the anterior aspect of the scleral tunnel. Beginning the suture placement in the floor of the tunnel will bury the knot in the grooved incision without the need for suture rotation (Fig. 8). No sutures are needed in the posterior aspect of the scleral tunnel and as no incisions are made in the conjunctiva, conjunctival closure is unnecessary (Fig. 9).
(Enlarge Image)
Figure 8.
A 10–0 nylon suture initiated in the base of the incision is utilized to close the wound.
(Enlarge Image)
Figure 9.
Bleb formation after closure of the tunnel opening with single horizontal 10–0 nylon suture.
Technique
Before beginning the surgical dissection, the location for the shunt placement should be determined. A region with minimal episcleral vascularization with small caliber vessels should be chosen and areas which have undergone previous scleral incisions for cataract surgery should be avoided. The superior bulbar conjunctival vessels can be constricted with a circular Merocel sponge soaked in phenylephrine 2.5% and placed for 10 to 15 minutes. In addition, a superior subconjunctival injection of xylocaine 1% with epinephrine helps constrict the episcleral vessels and reduce the severity of subconjunctival bleeding when the scleral dissection is opened into the subconjunctival space.
The first step of the procedure involves a clear corneal incision placed just anterior to the conjunctival insertion. This incision can be created with a diamond or steel-step knife and should be approximately 350 μm in depth and 4 mm in length (Fig. 1). A scleral pocket is then dissected posteriorly with a beveled crescent blade for approximately 3 mm ([Fig. 2). The scleral pocket is opened into the subconjunctival space with either the crescent knife or a sharp-tipped diamond or metal keratome (Fig. 3). Most recently, a Sharpoint 1.1 mm paracentesis knife (Model 78–2010) has been found to facilitate entry into the subconjunctival space (DAC). A 90-degree bend is made at the tip of the knife and after passing the knife into the sclera pocket with the bent tip parallel to the plane of dissection, the tip is rotated into a vertical orientation to perforate the roof of the pocket (Fig. 4). The tip is then used to slice a complete full-length opening into the subconjunctival space.
(Enlarge Image)
Figure 1.
A 4-mm long grooved incision is made with a 350 mm step-knife just anterior to the conjunctival insertion.
(Enlarge Image)
Figure 2.
A crescent knife is used to dissect a scleral pocket 3mm posterior to the grooved incision.
(Enlarge Image)
Figure 3.
The scleral pocket is opened into the subconjunctival space with a sharp-tipped keratome creating a scleral tunnel.
(Enlarge Image)
Figure 4.
A 1.1-mm paracentesis knife with the tip bent 90 degrees is used to open the sclera pocket into the subconjunctival space.
After completion of the scleral tunnel, the wound is then opened by placing a small skin hook or Kuglin hook under the roof of the scleral tunnel and a Sinskey hook within the corneal stroma of the anterior aspect of the grooved clear corneal incision. An assistant would hold the Sinskey hook while the surgeon holds the skin hook in their nondominant hand. With gentle opposing traction, the Sinskey hook will pull the external anatomic structures overlying the trabecular meshwork anteriorly as the skin hook retracts the roof of the scleral tunnel, thus exposing the site for the mini-shunt placement (Fig. 5). A 27-G needle with a bent tip is then inserted into the anterior chamber, just anterior to the posterior aspect of the blue zone that overlies the region of the trabecular meshwork (Fig. 6). The needle tip should be bent and inserted so that the resulting microincision is parallel to the plane of the iris. The Ex-PRESS shunt is then inserted into the incision, initially rotated 90 degrees from its ultimate final position (Fig. 7). Once it is seated with the external flange against the sclera, it is rotated 90 degrees into the proper orientation and the injector is squeezed to release the shunt. Although it is not possible to orient the shunt insertion in the iris plane because of the current limitations in the injector design and the limited anatomic exposure; a properly constructed perforating microincision and the overlying scleral tunnel roof apposed against the shunt's external flange will ultimately orient the shunt tip parallel with the iris.
(Enlarge Image)
Figure 5.
A skin hook retracts the roof of the scleral tunnel while a Sinskey hook pulls the external anatomic structures overlying the trabecular meshwork anteriorly, exposing the site for minishunt placement.
(Enlarge Image)
Figure 6.
A 27-G needle with a bent tip is inserted into the anterior chamber parallel to the iris and anterior to the posterior aspect of the blue zone.
(Enlarge Image)
Figure 7.
The Ex-PRESS shunt is inserted into the incision, initially rotated 90 degrees from its ultimate final position.
Once the shunt is in position, the hooks are removed and a single tangential 10–0 nylon suture is placed at the limbus to close the anterior aspect of the scleral tunnel. Beginning the suture placement in the floor of the tunnel will bury the knot in the grooved incision without the need for suture rotation (Fig. 8). No sutures are needed in the posterior aspect of the scleral tunnel and as no incisions are made in the conjunctiva, conjunctival closure is unnecessary (Fig. 9).
(Enlarge Image)
Figure 8.
A 10–0 nylon suture initiated in the base of the incision is utilized to close the wound.
(Enlarge Image)
Figure 9.
Bleb formation after closure of the tunnel opening with single horizontal 10–0 nylon suture.
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