Fig. 25.1
Diagram illustrating micropulsed diode laser energy delivery in a 15 % duty cycle. Laser turned on for 300 μs and off for 1,700 μs, thus on for 15 % of 2,000 μs envelope of cycle. Power of each application, 2.0 W, consists of 100 pulses, each of 4.0 mJ, delivered in 200 ms (0.2 s), thus 400 mJ (0.4 J) in 0.2 s, which is equal to 2.0 W (Illustration courtesy of IRIDEX Corp., Mountain View, CA)
In summary, the continuous wave laser system trabeculoplasty techniques use small focal spot sizes with large energy coagulation that spreads from the treatment sites. The short-pulsed systems use large spot sizes with relatively low-energy interaction that is confined to the treatment sites. The relative spot sizes for argon and diode continuous wave systems and for selective laser trabeculoplasty and micropulse diode laser trabeculoplasty (MDLT) are illustrated in Fig. 25.2. The treatment spot size for the continuous wave, frequency-doubled green Nd:YAG laser system is the same as that for argon laser systems.
Fig. 25.2
Laser spot sizes on trabecular meshwork during trabeculoplasty. Spot size for selective laser trabeculoplasty (SLT) (400 μm is larger than for micropulsed diode laser trabeculoplasty (MDLT) 300 μm). Both are much larger than coagulative trabeculoplasty spot sizes (50–75 μm) (Illustration courtesy of IRIDEX Corp., Mountain View, CA)
Methods of Trabeculoplasty Treatment
Preparation
There are several steps:
Informed consent for the type of laser surgery planned.
Topical anesthesia (e.g., tetracaine or proparacaine).
Appropriately antireflective-coated, gonioscopic treatment contact lens with methylcellulose 1 % solution for coupling with the eye surface.
Slit-lamp biomicroscope delivery system.
Anticipating posttreatment pressure spikes, some surgeons pretreat with topical Iopidine (apraclonidine) or brimonidine.
Continuous Wave Laser Systems
Treatment and Suggested Settings
Set laser system at spot size 50–75 μm, 0.4–1.0-W power, and 0.1-s duration.
Decide the extent of the circumference to be treated – 50 or 100 %.
Apply approximately 50 (for one-half the circumference treatment) or 100 (for circumferential treatment) evenly spaced laser applications, each aimed at the anterior border of the pigmented trabecular meshwork.
Adjust power during treatment for local blanching at the threshold for small bubble formation during laser applications [18].
Record the approximate percent of applications with blanching, bubble formation, or both in the procedure note.
Postoperative Care
For the first postoperative days, add topical steroid medication to the continued use of preoperative glaucoma medications.
Selective Laser Trabeculoplasty
Treatment and Suggested Settings
The selective laser trabeculoplasty (SLT) laser system (Lumenis, Inc., Santa Clara, CA) has a spot size of both the low-power helium–neon aiming beam and the treatment beam of 400 μm; the aiming beam is directed to cover the entire meridional height of the pigmented trabecular meshwork.
The initial energy setting for each treatment pulse is 0.8 mJ, with pulse energy adjustable from 0.2 to 1.7 mJ; pulse energy is adjusted during treatment to the threshold for small “champagne” bubbles within target tissue, which should occur in about half of the applications [30].
Decide the extent of the circumference to be treated: 50 or 100 %.
Using an appropriate treatment contact lens, apply approximately 50 (for one-half the circumference treatment) or 100 (for circumferential treatment) adjacent, nonoverlapping, evenly spaced laser applications, each aimed at the center of the pigmented trabecular meshwork.
In the procedure note, include the treatment parameters, including pulse energy, amount, and location of trabecular circumference treated, and number of applications.
Postoperative Care
For the first postoperative days, add topical nonsteroidal anti-inflammatory medication or steroid to the continued use of preoperative glaucoma medications; because the treatment effect depends upon a macrophage response, aggressive suppression of the inflammatory response is relatively contraindicated.
Micropulsed Diode Laser Trabeculoplasty
Treatment and Suggested Settings
The IQ 810 diode laser system with slit-lamp adaptor (IRIDEX Inc., Mountain View, CA) has an adjustable spot size of both the low-power helium–neon aiming beam and the treatment beam from 50 to 300 μm; use the 300-μm diameter and direct the aiming beam to center on the meridional height of the pigmented trabecular meshwork. This size usually covers the entire pigmented trabecular meshwork.
The laser system is set during system initiation to deliver individual applications consisting of a series of 100 micropulses, each with a duration of 0.3 ms (300 μs) and each followed by a 1.7 ms off-time (this is a 15 % “duty cycle”), all within a 200 ms (0.2 s) envelope. Each pulse delivers about 4 mJ. The power indicated in the system console represents the sum of the energy of all the pulses divided by the duration of the envelope; it is typically about 2,000 mW (2.0 W) (see Fig. 25.1). The short duration of each pulse of light within the envelope, followed by the comparatively long off-time, ensures localization of light energy to pigment granules within cells in the irradiated zone, without spread of coagulative heat to adjacent structures (Fig. 25.3). Thus, this treatment interaction resembles the tissue effect of SLT. These applications cause no observable change in the target tissue, so the doctor must pay diligent attention to the location of each application in order to achieve confluent coverage.
Fig. 25.3
Schematic interpretation of target tissue temperature elevation during and after trabecular laser treatment. Continuous wave (CW) laser treatment (a) causes rise to a plateau that decays when laser is turned off. Micropulsed responses (b–d) vary according to duty cycle. Short pulses with a long interval between pulses (low duty cycle) (b, c) cause brief thermal rise followed by decay before the next pulse arrives. Longer pulses (d) eventually cause buildup of tissue target thermal response (Illustration courtesy of IRIDEX Corp., Mountain View, CA)
Decide the extent of the circumference to be treated: 50 or 100 %.
Similar to SLT, apply approximately 50 (for one-half the circumference treatment) or 100 (for circumferential treatment) adjacent, nonoverlapping yet confluent, evenly spaced laser applications, each aimed at the center of the pigmented trabecular meshwork (Fig. 25.4).
Fig. 25.4
Anterior chamber angle drawing showing contiguous placement of selective laser trabeculoplasty and micropulsed laser trabeculoplasty applications. Since these applications cause little or no marks on angle tissue, the surgeon must be mindful of nearby landmarks in angle recess to guide sequential applications (Illustration courtesy of IRIDEX Corp., Mountain View, CA)
In the procedure note, describe the treatment parameters including system power setting, duration, duty cycle, amount, and location of trabecular circumference treated, and number of applications.
Postoperative Care Return
There is usually no need during the postoperative days to add topical nonsteroidal or steroidal anti-inflammatory medication, though the patient should continue use of preoperative glaucoma medications. These eyes have minimal to no clinically detectable inflammatory response. Treatment effect, similar to that after SLT, depends upon a macrophage response; thus, aggressive suppression of potential inflammation after the laser intervention is relatively contraindicated.
Complications and Problems
There may be one, or more, complications as follows:
Transient or, rarely, permanent blurred vision.
Transient inflammation (treat with anti-inflammatory medications, as discussed later).
Spike of IOP may be due to trabecular blockage from debris or inflammatory precipitates (treat with increased antiglaucoma medications, as discussed later).
Formation of PAS after continuous wave laser trabeculoplasty may be numerous, though usually localized and with a pillar shape, extending from the iris base to the middle of the pigmented trabecular meshwork.
Insufficient reduction of treated IOP from the preoperative baseline may require alternative management; if persistent, there may follow worsening of the visual field loss.
Expected Outcomes
Trabeculoplasty causes inflammation – more after treatment with continuous wave laser systems, some after SLT, and minimal to undetectable after MDLT. Most doctors prescribe topical anti-inflammatory medications for 4–7 days after continuous wave trabeculoplasty, a few days after SLT, and none after MDLT.
Pressure spikes may occur within an hour or two after continuous wave trabeculoplasty and occasionally after SLT. This response is usually of small magnitude, and, even if of larger magnitude, responds quickly to additional doses of topical antiglaucoma medications. Rarely, a sustained elevation of IOP follows continuous wave trabeculoplasty. In this situation, expedited filtering surgery or transscleral laser cyclophotocoagulation may be required. It is good if the patient has been warned about pressure elevation during the pretreatment discussion.
The beneficial IOP response to trabeculoplasty can be immediate or delayed. There is no way to predict ahead of time how quickly the response will start. In some patients, the IOP is lower within hours after treatment. In others, the response may develop slowly, over a period as long as 6 weeks. If possible, it is sensible to wait for as long as 6 weeks when there is no early beneficial response before moving to another treatment modality.
Of eyes in the Glaucoma Laser Trial Follow-Up Study (GLTFS) treated at glaucoma diagnosis with argon laser trabeculoplasty (ALT), 11 % had progressed by the end of the long-term follow-up, either needing filtering surgery or repeat argon laser trabeculoplasty. By contrast, of eyes in the GLTFS receiving medication as initial management, 34 % had needed either ALT or filtering surgery [31]. This result indicates an acceptable long-term effectiveness of initial ALT compared with initial medical treatment. In the Advanced Glaucoma Intervention Study (AGIS), which enrolled patients with medically uncontrolled, elevated IOP open-angle glaucoma, analysis of results was divided by self-reported race. Of eyes receiving ALT as the first surgical intervention, by Kaplan–Meier survival analysis at 5 years, there was a 30 % rate of failure among black patients and a 40 % rate of failure among white patients. In both subgroups, the rate increased to about 50 % by 10 years [32]. Thus, about half of eyes treated with ALT at the time of failure of medical management in the AGIS still had a successful status, with continued medical management, 10 years later. A similar assessment of long-term success is not yet available for eyes treated with SLT or MDLT (see Sidebar 25.1).
Sidebar 25.1. Comparing Laser Instruments
Yara Paula Catoira-Boyle2
(2)
Department of Ophthalmology, Indiana University School of Medicine, 702 Rotary Circle, 3rd Floor, Indianapolis, IN 46202, USA
The current traditional therapy algorithm for open-angle glaucomas includes laser trabeculoplasty (LTP), usually as the next step after medical therapy is insufficient to reach desired intraocular pressure (IOP). The laser energy is directed at the trabecular meshwork; it lowers IOP by improving the facility of outflow. LTP is a brief, minimally uncomfortable procedure with little risk of visual loss. It may be performed in the office setting or in an ambulatory surgery center. The most common postoperative complications are inflammation and a usually brief spike in IOP. These spikes are most often dealt with in a “routine” manner and should be discussed with the patient when obtaining informed consent to do the procedure. Because it is easy to perform and relatively risk-free for a surgical procedure, it is an important tool in the armamentarium of the glaucoma specialist and also for the general ophthalmologist who is comfortable with doing gonioscopy.
The indications for laser trabeculoplasty continue to evolve as newer laser modalities are developed. Despite the fact that the 1988 GLT (Glaucoma Laser Trial) and its follow-up study have shown argon laser trabeculoplasty (ALT) to be safe and as effective as medical therapy, ALT has not achieved the status of a primary therapy in the USA during the past 20 years. The newer selective laser trabeculoplasty (SLT) has been imputed to have some advantages over ALT and is currently being evaluated as primary therapy by many ophthalmologists.
Gonioscopy is performed on all patients who are being considered for laser treatment of their anterior chamber angles, to ensure that all structures are easily visible before performing LTP. The typical patient who may benefit from laser trabeculoplasty has mild-to-moderate glaucoma. They are aware that treatment options include medical therapy, laser treatment, and possibly incisional surgery. Patients in the USA will usually have failed to reach “target IOP” on medical therapy alone. Patients are told that laser therapy for their open-angle glaucoma should be thought of as an additional treatment, which if successful may or may not allow them to use less topical glaucoma medication postoperatively. They are also informed that even when successful, the IOP-lowering benefits of laser trabeculoplasty may only last for a period of months to years, but are not likely to be permanent.
In addition to glaucoma poorly controlled with the medical therapy, other important indications for LTP include poor compliance with drop regimens and difficulty using eye drops due to intolerance, allergic reaction, lifestyle considerations, or financial issues. Some patients may just prefer laser therapy over the need for chronic use of eye drops. SLT has been shown to successfully replace some medical therapy (average decrease from 2.79 to 1.5 drops) in patients with a target IOP of 16 ± 2 mmHg, with stable IOP 12 months later. Recently, SLT has also been shown to reduce IOP in patients with steroid-induced glaucoma after intravitreal Kenalog injections. It is reasonable to perform LTP even on patients with advanced disease, who have baseline IOP in the teens, and a desired target pressure in the single digits. Some of those instances include patients who are poor surgical candidates, or patients with glaucoma progression who are very reluctant to undergo incisional surgery and need a stepped approach or “last chance” for a conservative treatment. Patients with advanced glaucoma with IOP in the low teens (11–13 mmHg) on medical therapy can often achieve consistent IOPs of 9–10 mmHg after undergoing SLT.
Some patients are poor candidates for incisional surgery. They may be blind in one eye, they may have difficulty complying with postoperative instructions and necessary postoperative examinations, and they may simply refuse incisional surgery. Some elderly patients, while they have moderately advanced glaucoma, are not likely to suffer much additional functional loss or go blind for the remainder of their expected lifetimes. They really do not require the very low pressures that might be achieved with incisional surgery. For these patients, laser trabeculoplasty, while not the ideal procedure to lower intraocular pressure, may nonetheless be the best alternative.
Laser trabeculoplasty is not recommended for patients with IOPs higher than 35 mmHg, for those people who need their eye pressure lowered very quickly, or for those patients who have shown rapid progression of visual field defects or optic nerve damage.
Choices of Laser
Argon laser trabeculoplasty (ALT) was introduced in 1979. Diode laser trabeculoplasty (DLT) was shown to effectively lower IOP in 1990, and selective laser trabeculoplasty (SLT) was initially reported in 1995, becoming commercially available in 2002. Micropulse diode laser trabeculoplasty (MDLT) was first reported in 2005 using the same DLT diode laser set in the micropulse emission mode – instead of the conventional continuous wave (CW) emission mode – to minimize tissue damage and collateral effects and avoid scarring with the application of repetitive short diode laser pulses. MDLT was recently shown to control IOP for up to 12 months in 75 % of medically insufficiently controlled open-angle glaucoma (OAG) eyes that responded to treatment with an IOP reduction of ≥3 mmHg and maintaining IOP ≤ 21 mmHg.
Currently, there are three main options for laser trabeculoplasty: (a) the 514-nm CW argon laser or the newer 532-nm CW frequency-doubled Nd:YAG laser both used to perform ALT, (b) the 532-nm Q-Switched and frequency-doubled Nd:YAG laser used to perform SLT, and (c) the 810-nm CW and micropulsed diode laser that can be used to perform both DLT and MDLT.
Studies comparing the three laser modalities have shown IOP lowering to be comparable. Naturally, there is much more long-term experience with ALT. Due to the thermal coagulative damage that ALT and DLT cause to the trabecular meshwork (TM), the treatments should not be overlapped and should not be repeated in the same area of the TM because it may lead to elevation of IOP. For some physicians, it is routine to treat only 180° of angle, while some treat all 360° at one session. Thirty-four percent of patients in the GLT developed peripheral anterior synechiae (PAS), but the clinical implications of this are not clear. A similar amount of patients developed an IOP spike greater than 5 mmHg in the immediate postoperative period as opposed to 25 % reported for SLT, without pretreatment of IOP. With the addition of prophylactic topical apraclonidine or brimonidine, IOP spikes are cut to less than half.
The SLT stands out due to histopathologic studies that show absence of thermal or collateral damage to the nonpigmented cells or structure of the TM. The tissue effects of ALT, SLT, and MDLT in cadaver eyes have been compared in a study at the Wills Eye Institute in Philadelphia, Pennsylvania, with ALT showing coagulative and structural damage and both SLT and MDLT showing no morphologic change detectable at scanning electron microscopy. There is no formation of PAS with both SLT and MDLT. This absence of structural thermal damage makes the SLT and MDLT procedures theoretically repeatable without the pressure spikes that are common with repeat ALT. The immediate postoperative IOP spikes of greater than 5 mmHg are usually reported at about 10 % or less.
It has been reported that SLT reduces IOP in patients with a history of ALT. A study done at the Indianapolis Veterans Administration Hospital Eye Clinic, with patients on maximum-tolerated medical therapy who were poor surgical candidates, showed an additional average IOP reduction of 13 % after SLT. All patients had a history of at least 180° ALT.
ALT has been reported to work better in more pigmented angles, as in pigmentary glaucoma or pseudoexfoliation glaucoma. That is not the case with SLT, so those cases might do better with ALT, at least as initial laser therapy. SLT has been reported to have similar effect in pseudophakic and phakic patients. Finally, SLT requires less precise aiming of the laser beam, which makes it technically easier for training physicians and ophthalmologists with less experience in gonioscopy and angle surgery.
What Results to Expect
The long-term magnitude of IOP lowering with ALT and SLT has been found to be basically comparable in patients who have failed medical therapy or prior laser, with responses from 19 to 29 %. When used as primary therapy, SLT’s average IOP reduction was 31 % at 12 months. It seems primary therapy and higher baseline IOP (upper 20 s) are factors that lead to lower IOP results.
Regarding survival of response in patients on maximal medical therapy, success rates for IOP decreases of >3 mmHg and ≥20 % reduction without additional drops at 1, 3, and 5 years were 58, 38, and 31 %, respectively, for SLT and 46, 23, and 13 %, respectively, for ALT, but not statistically different. Another study showed success of SLT at 1, 2, 3, and 4 years at 60, 53, 44, and 44 %, respectively, with failure defined as need for any additional therapy, including another drop. Long-term evaluation of SLT as primary therapy is currently under way.
The rate of responders who achieved at least 20 % IOP reduction at 12 months was 59.7 % for SLT and 60.3 % for ALT. Those patients were on maximal medical therapy. When receiving SLT as primary therapy, responder rates with IOP lowering of ≥20 and ≥30 % at 12 months were 83 and 55 %. In the same study, patients who had been washed out of medications prior to SLT did not obtain as good results as primary SLT patients.
In conclusion, SLT and ALT are the most common modalities of laser trabeculoplasty currently used. Most of the time, the choice of laser will be dictated by what machine is available to the treating physician. The studies show that both lasers are probably good primary therapy modalities with the potential to reduce cost, side effects, and noncompliance with medications. Nevertheless, due to lack of scarring of the trabecular meshwork, SLT has a theoretical potential to be repeated several times on patients who had prior ALT or SLT and it is also technically easier to perform treatment with this device. LTP should be considered in patients who are not good candidates for surgical therapy. The effects of both laser treatments have been shown to last with decreasing effect after 1 year.
Bibliography
Chung PY, Schuman JS, Netland PA, et al. Five-year results of a randomized, prospective, clinical trial of diode vs Argon laser trabeculoplasty for open-angle glaucoma. Am J Ophthalmol. 1998;126(2):185–90.
Damji KF, Shah KC, Rock WJ, et al. Selective laser trabeculoplasty vs argon laser trabeculoplasty: a prospective randomized clinical trial. Br J Ophthalmol. 1999;83:718–22.
Damji KF, Bovell AM, Hodge WG, et al. Selective laser trabeculoplasty versus argon laser trabeculoplasty: results from a 1-year randomized clinical trial. Br J Ophthalmol. 2006;90:1490–4.
Fea AM, Bosone A, Rolle T, Brogliatti B, Grignolo FM. Micropulse diode laser trabeculoplasty (MDLT): a phase II clinical study with 12 months follow-up. Clin Ophthalmol. 2008;2(2):247–52.
Francis BA, Ianchulev T, Schofield JK, et al. Selective Laser trabeculoplasty as a replacement for medical therapy in open-angle glaucoma. Am J Ophthalmol. 2004;140(3):524–5.
Fudemberg SJ, Myers JS, Katz LJ. Trabecular meshwork tissue examination with scanning electron microscopy: a comparison of Micropulse diode Laser (MLT), Selective Laser (SLT), and Argon Laser (ALT) Trabeculoplasty in human cadaver tissue. Invest Ophthal Vis Sci. 2008;49:1236. ARVO E-Abstract.
Glaucoma Laser Trial Research Group. The Glaucoma Laser Trial (GLT). 2. Results of argon laser trabeculoplasty versus topical medicines. Ophthalmology. 1990;97(11):1403–13.
Glaucoma Laser Trial Research Group. The Glaucoma Laser Trial (GLT) and Glaucoma Laser Trial Follow-up Study: 7. Results. Am J Ophthalmol. 1995;120(6):718–31.
Hodge WG, Damji KF, Rock W, et al. Baseline IOP predicts selective laser trabeculoplasty success at 1 year post-treatment: results of a randomized clinical trial. Br J Ophthalmol. 2005;89:1157–60.
Ingvoldstad DD, Krishna R, Willoughby L. Micropulse diode laser trabeculoplasty. Invest Ophthal Vis Sci. 2005;46:123. ARVO E-Abstract.
Juzych MS, Chopra V, Banitt MR, et al. Comparison of long-term outcomes of selective laser trabeculoplasty versus argon laser trabeculoplasty in open-angle glaucoma. Ophthalmology. 2004;111(10):1853–9.
Latina MA, Sibayan SA, Shin DH, et al. Q-switched 532-nm Nd:YAG laser trabeculoplasty (selective laser trabeculoplasty): a multicenter, pilot, clinical study. Ophthalmology. 1998;105(11):2082–8.
Lunde M. Argon laser trabeculoplasty in pigmentary dispersion syndrome with glaucoma. Am J Ophthalmol. 1983;96:721–5.
McHugh D, Marshall J, Jffytche T, et al. Diode laser trabeculoplasty (DLT) for primary open-angle glaucoma and ocular hypertension. Br J Ophthalmol. 1990;74:743–7.
McIlraith I, Strasfeld M, Colev G, et al. Selective laser trabeculoplasty as initial and adjunctive treatment for open-angle glaucoma. J Glaucoma. 2006;15(2):124–30.
Melamed S, Simon GJB, Levkovitch-Verbin H. Selective laser trabeculoplasty as primary treatment for open-angle glaucoma. Arch Ophthal. 2003;121:957–60.
Ritch R, Liebermann J, Robin A, et al. Argon laser trabeculoplasty in pigmentary glaucoma. Ophthalmology. 1993;100:909.
Robin AL, Pollack IP. Argon laser trabeculoplasty in secondary forms of open angle glaucoma. Arch Ophthalmol. 1983;101:382–4.
Rubin B, Taglienti A, Rothman RF, et al. The effect of selective laser trabeculoplasty on intraocular pressure in patients with intravitreal steroid-induced elevated intraocular pressure. J Glaucoma. 2008;17(4):287–92.
Vishnu S, Catoira-Boyle Y, WuDunn D, et al. Efficacy of selective laser trabeculoplasty after argon laser trabeculoplasty in open angle glaucoma. Indianapolis, IN: Indiana University; 2007. ARVO poster 3971/B951.
Weinand FS, Althen F. Long-term clinical results of selective laser trabeculoplasty in the treatment of primary open angle glaucoma. Eur J Ophthalmol. 2006;16(1):100–4.
The Iris
Early in the 1960s, some of the first-tested applications of laser for the eye were iris treatment to create an iridotomy [3]. Iridotomy and iridoplasty are now among the more frequent laser treatments for glaucoma. These interventions are usually done for eyes with elevated IOP and angle closure, or for eyes with high-risk anatomic narrow angle. As with laser treatment for open-angle glaucoma, here again, gonioscopic skill is important. The surgeon has to recognize that the angle is closed, partly or completely, and whether the closure is appositional or due to formation of peripheral anterior synechiae (PAS), or a mix of the two. If PAS are present, it is important to determine the extent of the angle circumference involved.
In addition to iridotomy and iridoplasty as iris treatments, the occasional patient with miosis benefits from laser photomydriasis or laser sphincterotomy. These two laser treatments are usually justified by a need to improve vision or fundus visualization rather than a need to improve glaucoma status.
Iridotomy Indications and Contraindications
Angle closure may be acute, subacute, or chronic. Patients with angle closure often present with a chronic, indolent condition, suspected based on the Van Herick sign during slit-lamp examination [33]. Often, yet not always, these patients are hyperopic. They can be of any age, although the condition is more frequent among older individuals. The IOP is usually elevated, though it may be normal. Gonioscopy clarifies the extent of the anterior chamber angle blockage.
Occasionally the presentation is acute and dramatic. In the event of acute, marked IOP elevation, the cornea may have stromal or epithelial edema and may be hazy. The patient may have disabling pain and nausea. This interferes with gonioscopy and laser iridotomy (see Sidebar 25.2). Breaking the acute attack medically becomes important, as this relieves the pressure elevation and allows the cornea to clear. The patient may need systemic hyperosmotic agents in addition to topical agents to break the acute attack. In subacute presentations, the patient may have undergone repeated episodes of angle closure and have sector iris atrophy and numerous, small subcapsular lens opacities (glaukomflecken).
Sidebar 25.2. Corneal Edema Following Angle Closure: How to Perform Laser Iridotomy
Peter T. Chang3
(3)
Department of Ophthalmology, Baylor College of Medicine, 1977 Butler Road, Houston, TX 77030, USA
Corneal edema is a common sign in an acute angle-closure attack. The sudden and severe elevation of intraocular pressure (IOP) forces fluid into the cornea, overwhelming the capability of the endothelial pumps. While the edema may provide helpful information regarding the acute nature of IOP elevation, further ophthalmic examination may be impeded by the corneal opacity. Visualization of the anterior segment structures is often critical to an accurate, prompt diagnosis because other entities, such as neovascular glaucoma and other secondary angle-closure glaucomas, may also present with elevated IOP and corneal edema yet require different management modalities than pupillary block glaucomas. Inappropriate peripheral iridotomy could potentially exacerbate these other conditions. And of course, significant corneal edema in the case of angle closure secondary to pupillary block may preclude the ability to perform a laser peripheral iridotomy and necessitate incisional surgical intervention.
Any attempt to improve corneal edema should include antiglaucoma medications to lower the IOP. Aqueous suppressants and parasympathomimetics are preferred due to their quicker onset and mechanisms of action. Additionally, corneal edema can be reduced with the use of topical hypertonic agents, such as glycerin, as they draw water from the cornea by osmosis.
Instillation of topical glycerin causes significant burning or stinging, and it should, therefore, be preceded by use of a topical anesthetic agent. If glycerin is not readily available or if the use of glycerin does not yield significant reduction of corneal edema, anterior chamber paracentesis may be performed to lower IOP and to reduce corneal edema. Both the use of topical hyperosmotic agents and anterior chamber paracentesis may only temporarily clear the cornea, but they may do so for a sufficient amount of time to allow laser iridotomy to be performed.
My preferred technique for anterior chamber paracentesis was taught to me by my mentor, Dr. Paul Palmberg, at the Bascom Palmer Eye Institute. A half-inch, 30-gage needle is attached to a tuberculin syringe with the plunger removed. Following instillation of a topical anesthetic agent and a prep of the conjunctival sac and lashes with a povidone–iodine solution, the patient is positioned at the slit lamp with the lids held open either manually or with a wire speculum. A long entry path through the corneal stroma with this size needle almost eliminates the risk of wound leak. Entry into the anterior chamber through the limbus near 6 o’clock reduces the possibility of inadvertent injury to the crystalline lens in a phakic eye. The needle is withdrawn from the anterior chamber after approximately 20 s with the resultant IOP around 10 mmHg, as the small lumen of the 30-gage needle apparently prohibits flow against the atmospheric pressure at a lower IOP.
Paracentesis should be performed with caution as these patients often have severe pain and nausea. Overtly, short entry through the cornea may result in a leaky wound and, consequently, hypotony and increased risk for intraocular infection. Inadvertent trauma to the crystalline lens is also possible. Moreover, paracentesis in an eye with rubeosis irides may result in a significant hyphema and further elevation of IOP and worsening of visualization of anterior and posterior segment structures.
Alternatively to peripheral iridotomy, which requires reasonably clear cornea, laser gonioplasty or iridoplasty can be performed even through a relative hazy cornea. Laser iridoplasty may resolve the acute angle-closure attack in addition to facilitating a subsequent laser iridotomy by reducing corneal edema and should therefore be a part of an armamentarium of any glaucomatologist.
Bibliography
Arnavielle S, Creuzot-Garcher C, Bron AM. Anterior chamber paracentesis in patients with acute elevation of intraocular pressure. Graefes Arch Clin Exp Ophthalmol. 2007;245:345–50.
Lai JS, Tham CC, Lam DS. Limited argon laser peripheral iridoplasty as immediate treatment for an acute attack of primary angle-closure glaucoma: a preliminary study. Eye. 1999;13:26–30.
Lam DS, Lai JS, Tham CC. Immediate argon laser peripheral iridoplasty as treatment for acute attack of primary angle-closure glaucoma: a preliminary study. Ophthalmology. 1998;105:2231–6.
Luxenberg MN, Green K. Reduction of corneal edema with topical hypertonic agents. Am J Ophthalmol. 1971;71:847–53.
Mechanism of Angle Closure
Angle closure is usually the result of block of flow of aqueous humor from the posterior chamber through the pupil to the anterior chamber. Pupillary block is more likely when the pupil is in a mid-dilated state, as occurs when the patient is in a location with dim illumination (the theater or driving an automobile at night come to mind). The midperipheral iris balloons due to the slightly higher pressure in the posterior chamber; then, the ballooned iris may come into contact with the trabecular meshwork. The IOP becomes elevated when there is sufficient trabecular blockage by this “flap valve” effect. Creation of a small hole through the iris relieves the pressure inequality and allows the ballooned iris to return to a more normal location.
Other patients have a normal IOP associated with a narrow, yet slit open, crowded anterior chamber recess. Iridotomy will often relieve the high-risk status for these patients.
Despite a successful iridotomy, some patients have a persistent appositional angle closure due to plateau iris with forward rotation of the ciliary body. These patients are often hyperopic. The condition is discovered during gonioscopy after iridotomy and can be definitively diagnosed with ultrasonic biomicroscopy. In this situation, iridoplasty is often helpful. Iridoplasty seldom relieves synechial angle closure.
Iridectomy and Iridotomy
History
Iridectomy as an effective treatment for glaucoma dates to 1857, when Albrecht von Graefe made the initial report [34]. Not all glaucomatous eyes responded. Understanding the mechanism of pupillary block as the principal cause of angle closure was delayed until the publication of an explanation by Curran in 1920 [35]. Meyer-Schwickerath developed the xenon arc photocoagulator in the early 1950s and reported creating iridotomies with this noninvasive instrument in 1956 [36]. The instrument was cumbersome and the focused spot size large; it burned through the iris tissue in some patients, yet often caused burns of the nearby cornea and lens. With the availability of ophthalmic laser systems starting in the late 1960s, there followed a plethora of publications reporting iridotomy methods, success rates, long-term success, and complications with both continuous wave and high-power pulsed laser systems. These early studies are summarized [37].
Focusing treatment contact lenses, developed with high dioptric power and antireflective coating, facilitated the procedure [38–40]. After the original designs, eye surgeons developed lenses with features to enhance the iridotomy procedure, and many surgeons have readily adopted use of these special lenses. The Abraham lens has a 63-diopter treatment button. The Wise–Munnerlyn–Erickson lens has a 103-diopter treatment button. Lenses are available from commercial sources (Fig. 25.5). By the 1990s, techniques for iridotomy, iridoplasty, and pupilloplasty using these lenses were in wide use.
Fig. 25.5
Lenses for iridotomy. Abraham lens (upper left) has eccentric 66-diopter treatment button providing 1.5× image magnification and 0.67× treatment spot diameter reduction. Wise lens (lower left) has an eccentric 103-diopter treatment button providing 2.6× image magnification and 0.38× treatment spot diameter reduction. Pollack lens (upper right) combines a treatment button similar to the Abraham lens with a gonioscopic mirror to allow intraoperative anterior chamber angle viewing. Mandelkorn lens (lower right) has a large diameter viewing surface providing 1.2× image magnification and 0.83× laser treatment spot diameter reduction for iris periphery or lens capsule (Courtesy of Ocular Instruments, Inc., Bellevue, WA)
Goins et al. furthered the laser iridotomy procedure in 1990 with description of a method for iridotomy using argon laser pretreatment followed by high-power pulsed laser applications. This reduced the occurrence of bleeding that accompanied iridotomies done with pulsed laser systems alone and the complication of frequent late closure that followed argon laser iridotomy as it was done at that time [41].
The surgeon should be familiar with the guidance provided by the American Academy of Ophthalmology in the Preferred Practice Pattern for Primary Angle Closure, available online at http://one.aao.org/CE/PracticeGuidelines/default.aspx under Glaucoma in the Subspecialty Browser [42].
Methods of Iridotomy
Preparation
A hazy cornea, as in an acute angle-closure attack, precludes laser iridotomy. Topical or systemic medical glaucoma treatment, including hyperosmotic agents, to break the acute attack and lower the elevated IOP often clears the cornea allowing treatment to proceed.
Informed consent for the type of laser surgery planned.
Obtain a presurgery measurement of IOP.
Pretreatment with miotic – typically pilocarpine 1 or 2 % – drops to the eye to be treated about one-quarter to one-half hour before laser treatment.
Topical anesthesia (e.g., tetracaine or proparacaine).
Appropriate antireflective-coated, iridotomy treatment contact lens of choice with methylcellulose 1 % solution for coupling with the eye surface.
Slit-lamp biomicroscope delivery system adjusted with aiming beam centered in the on-axis slit beam and with laser confocal with microscope focus.
Anticipating posttreatment pressure spikes, some surgeons pretreat with Iopidine (apraclonidine) or brimonidine.
Treatment and Suggested Laser System Settings
The surgeon may find it advantageous to vary laser settings based on observation of tissue response during treatment.
Continuous Wave Laser Systems
Continuous wave (CW) systems include argon lasers and frequency-doubled green Nd:YAG systems.
The “chipping” technique provides better results with CW systems than slower, burning techniques.
Power 1,200 mW (1.2 W)
Duration 0.05 s
Spot size 50 μm
Q-Switched, High-Power, Nd:YAG Laser Systems
The “blasting” (disruptive) technique is better for lightly pigmented irides with noncompact stroma than for dense light-colored or deeply pigmented irides.
Energy per pulse usually 4.0–6.0 mJ (may be higher, though this approaches levels potentially causing crystalline lens damage).
Single pulses or bursts of three pulses.
Duration and spot size are an automatic characteristic of the system.
With the Q-switched pulsed system (prepared as indicated previously) ready to treat and the treatment site selected, make an initial tissue-disrupting application and observe the effect.
Make additional applications to exactly the same site, drilling deeper into the tissue.
Oozing of blood from disrupted small vessels will stop spontaneously or faster when pressure is applied to the eye with the treatment contact lens. Wait until the treatment site is again clearly visible. Subsequent applications may start the ooze again.
If brisk bleeding develops, stop it with pressure on the treatment contact lens and either choose another site or discontinue and postpone treatment to another day. The patient who has been forewarned about this rare possibility is not surprised if this situation develops during treatment.
The Combined CW and Pulsed Laser Technique
This is reliable and nearly always successful in one treatment session.
Start with the CW system (prepared as indicated previously) ready to treat.
Make two or three “chipping” applications close together on the tissue in a row parallel to the limbus to start a linear incision. Subsequent applications aimed at pigmented tissue in exactly the same site carry the opening into the iris stroma, deepening the cut.
About 30–50 applications will usually create small perforations to the posterior chamber, and puffs of pigmented debris enter the laser-created crypt. This often leaves devitalized, depigmented, or lightly pigmented strands across the base of the opening.
Next, move the patient to the Q-switched laser system, or move the system to the patient, with the system prepared as indicated previously and ready to treat. Reapply the treatment contact lens if it has come off the eye. Warn the patient that the laser makes a “snapping” sound when it comes to focus.
Provided the initial chipping burns have opened the tissue nearly to the posterior chamber, one laser Q-switched laser pulse, aimed carefully upon devitalized strands bridging the base of the treatment site, often suffices to open the iridotomy widely; if so, treatment is complete. Sometimes, more than one application is required. Successful applications often cause a large cloud of pigment particles and pigmented cellular debris to migrate from the posterior chamber to the anterior chamber, which usually deepens.
Treatment Site
The far peripheral upper nasal iris, under the lid, is the first choice – approximately the 12:30–1:30 meridian for the right eye and the 10:30–11:30 meridian for the left eye. Avoid the 12 o’clock meridian as bubbles formed during treatment will not move out of the way. Some ophthalmologists recommend a temporal site as this tends to reduce the possible complication of a postoperative ghost image or monocular diplopia.
The far peripheral upper temporal iris is an attractive alternative.
Treatment should not be so far peripheral that arcus senilis or the peripheral corneal vascular arcade interferes with the view of the treatment site.
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