Jeremy B. Wingard, MD and Joel S. Schuman, MD, FACS
Glaucoma laser surgery has changed in several respects since the last edition of this book. The replacement of argon laser trabeculoplasty in most practice settings with newer technologies, notably selective laser trabeculoplasty but also multipulse laser trabeculoplasty, has continued unabated. Further research has been performed on the role of endoscopic cyclophotocoagulation with or without cataract surgery. And finally, micropulse cyclophotocoagulation (CPC) has become available over the past few years, with a number of reports claiming utility of this treatment modality earlier in disease management than was common with diode CPC. The earlier use paradigm owes largely to the presumed tissue specificity of this laser, as compared to neodymium:yttrium-aluminum-garnet (Nd:YAG) or diode CPC, which tend to be destructive to surrounding ocular tissues. Although excimer laser trabeculotomy was discussed in the last edition of this text, it remains an uncommonly used technique.
Of course, lasers have remained useful in many of their traditional roles, including iridotomy for the treatment of angle-closure glaucoma or for prevention of angle closure in at-risk eyes; gonioplasty, to shrink the iris away from the trabecular meshwork in cases of early peripheral anterior synechiae or plateau iris; and laser suture lysis, to titrate intraocular pressure (IOP) after filtering surgery. Although less commonly utilized, laser procedures are potential treatments for failing blebs; to incise areas of episcleral or subconjunctival fibrosis; and in instances of hypotony, to coagulate, scar, and induce inflammation in the conjunctiva or to cause adhesion of the conjunctiva to the underlying episclera. Lasers may also be used to open the Descemet’s window left after canaloplasty, in the attempt to turn this surgery into a full-thickness, bleb-forming procedure or to clear obstructions, typically by iris tissue, of various implanted devices, such as the Ex-Press glaucoma filtration device (Alcon Laboratories), iStent (Glaukos), or any tube shunt. Historical, but no longer contemporary, laser uses included goniophotocoagulation, to ablate new blood vessels growing in the trabecular meshwork while waiting for panretinal photocoagulation to take effect, or for goniopuncture, in which the Nd:YAG laser is aimed at the trabecular meshwork to open channels into Schlemm’s canal, in cases such as juvenile open-angle glaucoma (JOAG) and angle-recession glaucoma, in which a hyaline-membrane has been thought to obstruct outflow.1–3
Each of these applications is covered in turn throughout the following chapters. Laser trabeculoplasty (LTP), which has gained a wider role throughout the spectrum of open-angle glaucoma management, continues to be extensively studied.4–19 Although the exact mechanism by which this procedure functions is still not known, insight has been gained into its workings and effects. In this way, realistic expectations allow the clinician to apply this technique in the appropriate settings, and to anticipate the outcome of such treatment. The past few years have shown the utility of selective laser trabeculoplasty as initial treatment for open-angle glaucoma or ocular hypertension,16 its value in the difficult to treat normal-tension glaucoma,17 and the relative long-term ineffectiveness of selective laser trabeculoplasty when IOP remains uncontrolled despite maximum medical therapy with the modern armamentarium of topical therapies.18 There has been a modest increase in our knowledge of the various effective LTP treatments modalities that have some reported success. A titanium-sapphire laser (790 nm) showed some potential utility for IOP lowering,19 adding to our knowledge that the effects of LTP are relatively wavelength independent, as nearly any photocoagulator, including the argon, diode,20,21 krypton, and continuous wave Nd:YAG laser (different from the Q-switched, pulsed Nd:YAG laser used for photodisruption), can be successfully employed for LTP. Micropulse laser trabeculoplasty, utilizing 100-microsecond pulses with a low duty cycle, thereby lowering total energy delivery, was introduced in the last edition of this book.22,23 Despite increased use of this laser, however, there is a paucity of peer-reviewed data available to recommend its place in clinical practice.
The pulsed Nd:YAG laser has remained the preferred instrument for performing laser peripheral iridectomy (LPI). We have learned that such iridectomies are, in fact, more likely to retain their patency than those created with the argon laser.24–29 Photocoagulators, such as those mentioned for LTP, have their place in LPI, as they coagulate blood vessels, thin the iris, and do not induce bleeding at the time of LPI; however, LPI is more efficient and long lasting when done with the Nd:YAG laser, or with a combination of a photocoagulator and photodisruptor.28,29
Contact transscleral laser CPC, with either Nd:YAG or diode laser, has been the preferred cyclodestructive therapy in late-stage and refractory glaucoma since the fourth edition was published, having supplanted cyclocryotherapy at that time. These lasers remain in common use and are particularly effective when surgical options have failed or when incisional therapy is not possible for medical, social, or other reasons. Contact transscleral Nd:YAG or diode laser CPC causes little postoperative discomfort but carries with it the same risks for hypotony and visual loss as cyclocryotherapy; therefore, laser CPC remains a procedure of last resort in the majority of practices. Endoscopic cyclophotocoagulation was introduced in the fifth edition of this text and remains in use, allowing direct intraoperative diode laser application to the ciliary processes without the same degree of tissue destruction as transscleral CPC.30–41 This relative safety has led some practitioners to use endoscopic cyclophotocoagulation as a cyclodestructive procedure much earlier in the course of disease, although risks of hypotony and vision loss remain.42 Additionally, the recent commercialization of multipulse transscleral contact CPC (Iridex), which breaks up the delivered diode laser energy into short bursts, has led some practitioners to utilize nonincisional cyclodestruction much earlier in the disease process. Clinicians may be encouraged that this technique should limit thermal damage, and available results, while minimal with respect to peer-reviewed and published data, are encouraging.23
Laser sclerectomy remains a technique in evolution. A variety of lasers have been investigated for this application, including recently a CO2 laser system with promising results,43 although randomized clinical trials are lacking to date. The prospect for this procedure is tantalizing: a minimally invasive means by which to perform filtering surgery, with little or no conjunctival manipulation, perhaps even performed in the office. Work has also been completed in the related area of laser trabeculotomy, an attempt to treat the juxtacanalicular outflow obstruction believed to be the site of primary pathology in most open-angle glaucoma patients, without scleral perforation and therefore no filtering bleb. There has been one prospective, randomized study that showed promising results for ab interno laser trabeculotomy with the 308 nm xenon-chloride excimer laser,44 although recent published work on the topic is lacking.
The list of miscellaneous procedures continues to grow as our experience with lasers increases. Gonioplasty is useful in eyes with angle closure despite a patent iridectomy, either to break peripheral anterior synechiae formed within the previous 6 months45 or to thin the peripheral iris. Laser suture lysis allows titration of IOP in the early postoperative period but carries with it the risks of hypotony and conjunctival bleb leak (due to an inadvertent conjunctival burn). Laser treatment of the bleb tissue, using an absorbing dye, such as 2% fluorescein, methylene blue, or indocyanine green, is effective in some cases of overfiltration with hypotony, inducing conjunctival contraction, scarring, and adhesion to the underlying sclera. Goniophotocoagulation is rarely performed, as immediate treatment of neovascularization, during the waiting period for panretinal photocoagulation effect, is routinely, and more successfully, treated by intravitreal injections of anti–vascular endothelial growth factor inhibitors, which are widely available and even serve as chronic substitutes for panretinal laser in certain cases.
Each of these “miscellaneous” procedures requires the use of a photocoagulator, and each can be done with an argon or diode laser (or others). To incise tissue, such as is necessary when treating a failing bleb or for goniopuncture, the pulsed Nd:YAG laser is needed. This is the same laser used for LPI or capsulotomy. Other pulsed lasers, such as the picosecond laser or excimer laser, although not widely available, can also be used for this task.
An overview of glaucoma laser therapy is presented in Tables 52-1 and 52-2.
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