Nd: YAG Laser Goniopuncture
Nd: YAG Laser Goniopuncture
To perform goniopuncture, a well-formed Descemet window must be present, extending approximately 300 to 500 μm anterior to Schwalbe line. Descemet window is best formed with blunt dissection at the base of the deep scleral flap to detach Schwalbe line, lifting the corneal stroma away from Descemet membrane and leaving a very thin, clear window for aqueous percolation (Fig. 1). Other methods such as using a cutting instrument instead of blunt dissection can leave a significant amount of corneal stroma on Descemet membrane as well as a significantly increased likelihood of penetration into the anterior chamber. In addition to the risk of perforation, insufficient dissection of corneal stroma off Descemet window will result in a more challenging situation in which to perform goniopuncture.
(Enlarge Image)
Figure 1.
A, Canaloplasty surgical site and corresponding ultrasound (B) and gonioscopy (C) views. The thin, clear trabeculo-Descemet window is anterior to the trabecular meshwork. SL indicates scleral lake; SS, scleral spur; TM, trabecular meshwork; TDW, trabeculo-Descemet membrane.
During creation of Descemet window, the focus of the surgeon should be to obtain the correct dissection plane on each radial side of the deep scleral flap rather than the central separation of Descemet membrane from corneal stroma. Although in some patients the Descemet membrane is more firmly adherent to the corneal stroma than in others, central separation typically occurs readily if the correct depth is achieved along the radial deep scleral flap dissection. The preferred technique of the authors involves carefully dissecting down to expose the choroid at the posterior aspect of the deep scleral flap providing the surgeon with a visual assessment of the required thickness of the deep flap. With the intended plane designed to leave a bed of sclera approximately 100 μm thick, the deep flap dissection is carried forward until the scleral spur is identified. A paracentesis incision should then be created to lower the IOP to single digits before unroofing Schlemm canal. This reduces the outward bulging of Descemet membrane and reduces the likelihood of perforation during deep flap dissection. With upward traction on the deep flap, the radial sides should gently be carried forward into clear cornea until the desired size of Descemet window is achieved. If necessary, a moistened weck-cel sponge can be used to depress Descemet window to achieve separation of the corneal stroma, although in the authors' experience this usually occurs readily without any manipulations. Alternatively, the canaloplasty manipulator instrument (Rhein Medical, St Petersburg, FL), which resembles a modified Drysdale spatula, can be used to separate Descemet window from corneal stroma.
Intraoperative Creation of Descemet Window
To perform goniopuncture, a well-formed Descemet window must be present, extending approximately 300 to 500 μm anterior to Schwalbe line. Descemet window is best formed with blunt dissection at the base of the deep scleral flap to detach Schwalbe line, lifting the corneal stroma away from Descemet membrane and leaving a very thin, clear window for aqueous percolation (Fig. 1). Other methods such as using a cutting instrument instead of blunt dissection can leave a significant amount of corneal stroma on Descemet membrane as well as a significantly increased likelihood of penetration into the anterior chamber. In addition to the risk of perforation, insufficient dissection of corneal stroma off Descemet window will result in a more challenging situation in which to perform goniopuncture.
(Enlarge Image)
Figure 1.
A, Canaloplasty surgical site and corresponding ultrasound (B) and gonioscopy (C) views. The thin, clear trabeculo-Descemet window is anterior to the trabecular meshwork. SL indicates scleral lake; SS, scleral spur; TM, trabecular meshwork; TDW, trabeculo-Descemet membrane.
During creation of Descemet window, the focus of the surgeon should be to obtain the correct dissection plane on each radial side of the deep scleral flap rather than the central separation of Descemet membrane from corneal stroma. Although in some patients the Descemet membrane is more firmly adherent to the corneal stroma than in others, central separation typically occurs readily if the correct depth is achieved along the radial deep scleral flap dissection. The preferred technique of the authors involves carefully dissecting down to expose the choroid at the posterior aspect of the deep scleral flap providing the surgeon with a visual assessment of the required thickness of the deep flap. With the intended plane designed to leave a bed of sclera approximately 100 μm thick, the deep flap dissection is carried forward until the scleral spur is identified. A paracentesis incision should then be created to lower the IOP to single digits before unroofing Schlemm canal. This reduces the outward bulging of Descemet membrane and reduces the likelihood of perforation during deep flap dissection. With upward traction on the deep flap, the radial sides should gently be carried forward into clear cornea until the desired size of Descemet window is achieved. If necessary, a moistened weck-cel sponge can be used to depress Descemet window to achieve separation of the corneal stroma, although in the authors' experience this usually occurs readily without any manipulations. Alternatively, the canaloplasty manipulator instrument (Rhein Medical, St Petersburg, FL), which resembles a modified Drysdale spatula, can be used to separate Descemet window from corneal stroma.
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