Aductive laser iridoplasty and laser goniopuncture after non-perforating trabeculectomy.

BACKGROUND

Successful non-perforating trabeculectomy (NPT) results in filtration of aqueous humor out of the anterior chamber and into a filtration bleb, without surgical excision of tissue from the anterior chamber angle, and without penetration into the anterior chamber. The complications of perforating trabeculectomy, due to early postoperative hypotony (shallow anterior chamber, hyphema, macular folds, suprachoroidal effusion, and ciliochoroidal hemorrhage) (3, 4, 5, 6, 7, 8, 9) are regarded by many surgeons as significant risks. Nonperforating surgery has been reported to reduce the incidence of early hypotony-related complications (10), because it has the advantage of creating gradual filtration of aqueous humor, through a thin trabeculodescemetic membrane (TDM), which markedly reduces postoperative complications seen after a conventional trabeculectomy (11), and also has been reported to provide better long-term intraocular pressure (IOP) control (12, 13). NPT is reported to be a procedure with a significant learning curve, sometimes necessitating conversion to perforating trabeculectomy, and requiring careful postoperative monitoring (14, 15, 16, 17). Zimmerman et al. reported filtration of aqueous humor under a filtering bleb, by resecting the roof of Schlemms canal and removing corneal stroma overlying the trabecular meshwork (18) Mermoud et al. reported filtration of aqueous humor under a filtering, bleb by unroofing Schlemms canal and removing corneal stroma overlying the trabecular meshwork as well Descemets membrane (19); he found that resistance across the TDM sometimes increased with time. When this resistance to aqueous humor outflow occurred, Mermoud found TDM resistance could be eliminated by performance of goniopuncture (ab interno Nd:YAG laser membranotomy via gonioprism), to enhance aqueous humor outflow into the filtration bleb. Failure to filter adequately through the TDM is a potential complication following NPT which can result in a rise in intraocular pressure (IOP). In this paper we examine the effectiveness of adjunctive Nd:YAG laser goniopuncture (YGP) in patients who underwent NPT, to reduce post-operative IOP rise, secondary to scarring at or poor aqueous outflow through the TDM. Iris prolapse (IP) is another potential complication following NPT which can result in a rise in IOP. In this paper we examine the effectiveness of adjunctive argon laser peripheral iridoplasty (ALPI) in patients who underwent NPT, to reduce post-operative IOP rise, secondary to IP obstructing outflow across the TDM.

BACKGROUND

Nd:YAG laser goniopuncture consists of placing several laser shots on the undersurface of the trabeculodescemetic membrane. The result is a microperforation in this membrane, with flow of aqueous into the filtration bleb, which converts a non-perforating filtration procedure into a partial thickness filtration procedure. In this technique, several high power, multi-burst shots are applied, ab interno, by a Nd:YAG laser via a gonioprism, to the underside of the TDM, to facilitate aqueous outflow out from the anterior chamber. YGP can be effective when increased aqueous outflow is desired postoperatively. After this procedure, patent perforation in the TDM is usually observed gonioscopically, generally accompanied with reduction in IOP, and increase in bleb elevation (in height and in circumferential extent). Argon laser peripheral iridoplasty consists of placing several laser burns on the surface of the peripheral iris to contract the iris stroma, in a centripetal fashion, between the site of the burn and the anterior chamber angle. The result is iris stromal tissue contraction and compaction, movement of IP away from the angle and toward the pupil, which physically widens the angle and clears the synechial apposition of the peripheral iris against the TDM. In this technique, a series of low power, long duration, and large size burns is applied to the iris periphery to contract the iris stroma, to open the angle, and to clear IP causing synechial obstruction of the TDM after successful NPT. Used previously in acute angle closure glaucoma, ALPI may be effective in controlling IOP and clearing corneal edema when systemic and topical anti-glaucoma treatments fail to control high IOP, and when laser peripheral iridotomy (LPI) is not possible (e.g. in cases of severe corneal edema). Additionally, ALPI can be effective in permanently reopening the anterior chamber angle of iridectomized eyes with plateau iris syndrome; in this technique a full 360 degrees ring of spots is often applied, but a more limited area of treatment may also be effective.

METHODS

When a post-operative elevation in IOP was detected in a patients eye which had undergone NPT, careful indentation gonioscopy was performed to examine the TDM at the surgical site. If the peripheral iris was flat, the anterior chamber angle was open, and the TDM did not appear obstructed by IP, YGP was performed. First, the eyes were pre-treated with aproclonodine 1% and pilocarpine 2% (if needed to allow visualization of the TDM). Next, a Nd:YAG laser was set on triple burst mode and shots were applied to the underside of the TDM at the NPT site, using a Goldman 3-mirror lens in the following manner: Energy - 3-5 mJ; Mode - Triple burst. The power and amount of spots were titrated in order to achieve partial or microperforation of TDM at the NPT surgical site, thus resulting in restoration of aqueous outflow into the filtration bleb. When a post-operative elevation in IOP was detected in a patients eye which had undergone NPT and or YGP, careful indentation gonioscopy was performed to examine the TDM at the surgical site. If irreducible synechial IP were detected, which obstructed filtration through the TDM at the NPT surgical site, ALPI was performed. First, the eyes were pre-treated with aproclonodine 1% and pilocarpine 2%. Next, an argon laser was set on blue-green mode and shots were applied to the IP adherent to cornea or to the TDM at the NPT site, using a Goldman 3-mirror lens in the following manner: Spot Size - 500 mM; Duration - 0.5 s; Power - 200 to 400 mW. The power and amount of burns were titrated in order to achieve partial or complete centripetal retraction of the IP from the TDM at the NPT surgical site, causing a clearance of the obstruction to the TDM, thus resulting in restoration of aqueous outflow into the filtration bleb.