Nd: YAG Laser Goniopuncture
Nd: YAG Laser Goniopuncture
The equipment required to perform this procedure and appropriate laser settings are listed in Table 1 and a step-by-step procedural summary can be found in Table 2. Any glaucoma medications should be continued until a postprocedure follow-up visit. If the IOP is >25 mm Hg, it is advisable to reduce the IOP to <25 mm Hg with an [alpha]-agonist (brimonidine or apraclonidine) and [beta]-blocker as laser goniopuncture in the presence of an elevated IOP increases the risk of iris incarceration into the goniopuncture site. In addition, with significant decreases in IOP pregoniopuncture to postgoniopuncture, there is a greater possibility of iris incarceration. Preoperatively, the application of a miotic such as pilocarpine, apraclonidine for its vasoconstrictive properties, and a topical nonsteroidal anti-inflammatory agent may be considered and are typically recommended. The use of preprocedure pilocarpine can be avoided in high myopes with wide anterior chamber angles and in certain patients the surgeon may notice a slight shallowing of the anterior chamber resulting in a mild increase in difficulty visualizing the TDW.
A mirrored gonioscopy contact lens (eg, CGAL, Haag-Streit, Koeniz, Switzerland), should be positioned for optimal viewing of the surgical site with the observer trying to discern a subtle difference in the appearance of the peripheral cornea, which can be described as a light opalescence. With the Q-switched Nd:YAG laser at 1064 nm, a zero offset should be used so that the beam will converge precisely on the TDW. The anatomic target for goniopuncture is preferably Descemet's portion of the semitransparent, diaphanous TDW. It can be challenging to localize the beam to the TDW, so the beam should be targeted approximately 150 to 200 μm anterior to Schwalbe line choosing a thinner portion of the window and initially aiming centrally (Fig. 4). The authors recommend beginning with single shots of approximately 3 mJ similar to posterior capsulotomy. The treatment can be intensified with multiple shots, 2 or 3 pulses per burst, and by gradually increasing the energy to generally no more than 5 or 6 mJ until the TDW is punctured.
(Enlarge Image)
Figure 4.
Gonioscopic view subsequent to canaloplasty showing the delineation of the trabeculo-Descemet window (TDW) and 2 trabecular tensioning suture knots in Schlemm canal. When performing goniopuncture, the beam should be targeted approximately 150 to 200 mm anterior to Schwalbe line choosing a thinner portion of the window, initially aiming centrally. The blue stars represent where the targeting beam should be aimed.
The surgeon should look carefully for a hole, fracture, slit, scroll of tissue, or flap, which has formed in the TDW (Table 3). It can be challenging to see if one has successfully lasered through the TDW as pigment may be released into the anterior chamber during the procedure as well as air bubbles or occasionally blood, so the surgeon should look for subtle changes in the appearance of the overall window such as a slight change in window concavity or the detection of a scroll in Descemet membrane (Fig. 5). Descemet window can be thin and transparent so any pigment on the window may facilitate the location of the target tissue to be lasered. To assist in visualizing a postlaser patency in the TDW, one may compress the eye with the goniolens and observe for aqueous flow through the opening or a moving flap of TDW adjacent to the goniopuncture site. If bubbles have formed in the anterior chamber, they may travel through the TDW into the scleral lake confirming penetration. However, tracking bubbles accurately near the opening can be deceiving as it can be difficult to achieve a clear view through the window. The authors attempt to produce 2 holes, preferably 3, in the TDW, although on occasion, 1 laser application may produce a large linear slit obviating the need for multiple laser applications. The resultant opening does not have to be large. A small opening is adequate to reestablish useful flow, but it must be situated as anteriorly as possible to minimize the risk of iris prolapse and incarceration.
(Enlarge Image)
Figure 5.
Gonioscopic view showing scrolls of Descemet membrane in the trabeculo-Descemet window subsequent to goniopuncture.
In high-risk cases such as patients with narrow angles, it is of even greater importance to attempt to lower the IOP to <25 mm Hg preprocedure. Pilocarpine should be administered immediately before the procedure and possibly added to the postprocedure regimen to prevent iris incarceration. A prophylactic, localized argon iridoplasty may also be performed. The authors advise following these patients more closely in follow-up after laser goniopuncture. A narrow angle is a relative contraindication for nonpenetrating glaucoma surgery due to the increased postoperative risk of iris adhesion to the TDW in these eyes, which is further increased after goniopuncture. Should iris incarceration occur, the IOP may abruptly rise in both narrow or open-angle configurations.
During canaloplasty surgery, a target Descemet window size of approximately 500 μm is desired so that goniopuncture can be performed easily in the postoperative period without inadvertently rupturing the intracanalicular prolene sutures. After goniopuncture, the suture stent can retract somewhat based on the degree of suture tensioning present. In the case of deep sclerectomy with collagen implant, the implant may actually block outflow. If the collagen implant is situated at the anterior window, surgeons should cautiously laser next to the wick.
Equipment and Technique
The equipment required to perform this procedure and appropriate laser settings are listed in Table 1 and a step-by-step procedural summary can be found in Table 2. Any glaucoma medications should be continued until a postprocedure follow-up visit. If the IOP is >25 mm Hg, it is advisable to reduce the IOP to <25 mm Hg with an [alpha]-agonist (brimonidine or apraclonidine) and [beta]-blocker as laser goniopuncture in the presence of an elevated IOP increases the risk of iris incarceration into the goniopuncture site. In addition, with significant decreases in IOP pregoniopuncture to postgoniopuncture, there is a greater possibility of iris incarceration. Preoperatively, the application of a miotic such as pilocarpine, apraclonidine for its vasoconstrictive properties, and a topical nonsteroidal anti-inflammatory agent may be considered and are typically recommended. The use of preprocedure pilocarpine can be avoided in high myopes with wide anterior chamber angles and in certain patients the surgeon may notice a slight shallowing of the anterior chamber resulting in a mild increase in difficulty visualizing the TDW.
A mirrored gonioscopy contact lens (eg, CGAL, Haag-Streit, Koeniz, Switzerland), should be positioned for optimal viewing of the surgical site with the observer trying to discern a subtle difference in the appearance of the peripheral cornea, which can be described as a light opalescence. With the Q-switched Nd:YAG laser at 1064 nm, a zero offset should be used so that the beam will converge precisely on the TDW. The anatomic target for goniopuncture is preferably Descemet's portion of the semitransparent, diaphanous TDW. It can be challenging to localize the beam to the TDW, so the beam should be targeted approximately 150 to 200 μm anterior to Schwalbe line choosing a thinner portion of the window and initially aiming centrally (Fig. 4). The authors recommend beginning with single shots of approximately 3 mJ similar to posterior capsulotomy. The treatment can be intensified with multiple shots, 2 or 3 pulses per burst, and by gradually increasing the energy to generally no more than 5 or 6 mJ until the TDW is punctured.
(Enlarge Image)
Figure 4.
Gonioscopic view subsequent to canaloplasty showing the delineation of the trabeculo-Descemet window (TDW) and 2 trabecular tensioning suture knots in Schlemm canal. When performing goniopuncture, the beam should be targeted approximately 150 to 200 mm anterior to Schwalbe line choosing a thinner portion of the window, initially aiming centrally. The blue stars represent where the targeting beam should be aimed.
The surgeon should look carefully for a hole, fracture, slit, scroll of tissue, or flap, which has formed in the TDW (Table 3). It can be challenging to see if one has successfully lasered through the TDW as pigment may be released into the anterior chamber during the procedure as well as air bubbles or occasionally blood, so the surgeon should look for subtle changes in the appearance of the overall window such as a slight change in window concavity or the detection of a scroll in Descemet membrane (Fig. 5). Descemet window can be thin and transparent so any pigment on the window may facilitate the location of the target tissue to be lasered. To assist in visualizing a postlaser patency in the TDW, one may compress the eye with the goniolens and observe for aqueous flow through the opening or a moving flap of TDW adjacent to the goniopuncture site. If bubbles have formed in the anterior chamber, they may travel through the TDW into the scleral lake confirming penetration. However, tracking bubbles accurately near the opening can be deceiving as it can be difficult to achieve a clear view through the window. The authors attempt to produce 2 holes, preferably 3, in the TDW, although on occasion, 1 laser application may produce a large linear slit obviating the need for multiple laser applications. The resultant opening does not have to be large. A small opening is adequate to reestablish useful flow, but it must be situated as anteriorly as possible to minimize the risk of iris prolapse and incarceration.
(Enlarge Image)
Figure 5.
Gonioscopic view showing scrolls of Descemet membrane in the trabeculo-Descemet window subsequent to goniopuncture.
In high-risk cases such as patients with narrow angles, it is of even greater importance to attempt to lower the IOP to <25 mm Hg preprocedure. Pilocarpine should be administered immediately before the procedure and possibly added to the postprocedure regimen to prevent iris incarceration. A prophylactic, localized argon iridoplasty may also be performed. The authors advise following these patients more closely in follow-up after laser goniopuncture. A narrow angle is a relative contraindication for nonpenetrating glaucoma surgery due to the increased postoperative risk of iris adhesion to the TDW in these eyes, which is further increased after goniopuncture. Should iris incarceration occur, the IOP may abruptly rise in both narrow or open-angle configurations.
During canaloplasty surgery, a target Descemet window size of approximately 500 μm is desired so that goniopuncture can be performed easily in the postoperative period without inadvertently rupturing the intracanalicular prolene sutures. After goniopuncture, the suture stent can retract somewhat based on the degree of suture tensioning present. In the case of deep sclerectomy with collagen implant, the implant may actually block outflow. If the collagen implant is situated at the anterior window, surgeons should cautiously laser next to the wick.
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