1 Comment

Chapter 235 – Argon Laser Trabeculoplasty and Peripheral Iridectomy

Chapter 235 – Argon Laser Trabeculoplasty and Peripheral Iridectomy

 

IOANNIS M. ASLANIDES

L. JAY KATZ

 

ARGON LASER TRABECULOPLASTY

INTRODUCTION AND HISTORICAL REVIEW

Argon laser trabeculoplasty (ALT) is an established, well-tolerated procedure used to lower intraocular pressure (IOP) in various types of open-angle glaucoma.[1] (Laser treatment of the human trabecular meshwork by puncturing Schlemm’s canal was performed initially by Krasnov in 1973, but the lower IOP he described was short-lived. [1] ) In 1979, Wise and Witter[2] reported that the placement of small, evenly spaced, nonpenetrating argon laser spots consistently lowered IOP in phakic eyes that have open-angle glaucoma.

PREOPERATIVE EVALUATION AND DIAGNOSTIC APPROACH

Positive and negative predictors for ALT success include diagnosis, pigmentation of the trabecular meshwork, age, and angle configuration ( Table 235-1 ). For patients younger than 50 years of age, ALT is not recommended unless they have pigmentary or pseudoexfoliation glaucoma. With optimal patient selection, after ALT, IOP typically drops 25–30% below the initial IOP. However, whether ALT yields the same success rate in African Americans as in Caucasians is controversial.[3]

GENERAL TECHNIQUES

Patient Preparation

If the angle is closed or narrow, a laser iridoplasty or a peripheral iridectomy is performed beforehand to deepen and allow better visualization of the angle; a laser iridoplasty is often performed simultaneously with ALT, but when a peripheral iridectomy is performed, ALT is done a week later because of possible anterior chamber debris. The patient’s informed consent must be sought after a thorough discussion of the goal of therapy and potential complications.

A drop of apraclonidine 0.5% or brimonidine 0.2% is instilled in the eye 30–60 minutes preoperatively to minimize IOP elevation after treatment. Proparacaine 0.5% drops are instilled immediately before the procedure.

Lens Choice

A Ritch[4] or, more commonly, a three-mirror Goldmann lens with antireflective coating is used. It features a dome-shaped mirror angled at 59° to visualize the angle. The lens does not invert the image but reverses the position, such that the 12 o’clock position of the mirror represents the 6 o’clock position at the angle, the 1 o’clock position of the mirror represents the 5 o’clock position at the angle, and so forth. (Methylcellulose is used as a coupling agent between the cornea and the lens.)

 

 

TABLE 235-1 — POSITIVE AND NEGATIVE PREDICTORS OF ARGON LASER TRABECULOPLASTY SUCCESS

 

Negative Predictors

Positive Predictors

Age (years)

<40

>65

Trabecular meshwork pigmentation

Little or none

Moderate to marked

Corneal clarity

Poor

Clear

Disease entities

Uveitic glaucoma

Pigmentary glaucoma

 

Angle closure

Pseudoexfoliative glaucoma

 

Juvenile glaucoma

Primary open-angle glaucoma

 

Angle recession

Low-tension glaucoma

Lens status

Aphakic or anterior chamber intraocular pseudophakia

Phakic or posterior chamber intraocular pseudophakia

Contralateral eye

Little effect

Strong effect

 

 

Equipment Preparation

The physician checks the laser settings and surveys the angle structures again. (The trabecular meshwork always lies between two white lines [Schwalbe’s line and the scleral spur]. However, the trabecular meshwork may occasionally be variably pigmented, and a pigmented Schwalbe’s line or a ciliary body band may be confused with the trabecular meshwork.)

The procedure begins with the goniolens at the 12 o’clock position (inferior angle), and the lens is rotated clockwise; the temporal portion of the right eye and the nasal portion of the left eye are photocoagulated first. To ensure delivery of laser energy with maximal efficiency, the aiming beam is always kept in the center of the mirror, round and sharp, keeping the goniolens perpendicular to the laser beam; also, it is rotated after several applications.

Treatment Guidelines

The laser spots are placed at the junction of the pigmented and nonpigmented trabecular meshwork, with a gap of about the diameter of two laser spots between spots ( Fig. 235-1 , A). The authors currently treat 360° of the angle in one session (20–25 spots per quadrant). Commonly used parameters are a 50?µm spot size, 0.1?sec duration, and 200–800?mW of power. Settings should be adjusted according to the tissue reaction end point, which is minimal blanching (see Fig. 235-1 , B). If the burn is too anterior, the treatment is more likely to be ineffective; if it is too posterior, it is more likely to create inflammation and peripheral anterior synechiae.

 

1558

 

 

Figure 235-1 Laser treatment of trabecular meshwork. A, Optimal laser beam placement on the trabecular meshwork. (With permission from Schwartz AL, et al. J Glaucoma. 1993;2:329.) B, Trabecular meshwork tissue end point reaction to different intensities of argon laser treatment. (Reproduced with permission from Schwartz AL, et al. Ophthalmology. 1987;88:203.)

Wavelength

Argon green laser appears to be effective and is less likely to cause photoreceptor injury to the treating physician than is argon blue-green laser. Diode laser has been used with comparable results, but the tissue reaction is less pronounced, making it harder to judge the end point.

Follow-up

The IOP is measured 1 hour after ALT. If it is elevated, an additional antiglaucoma medication (aqueous suppressant, miotic, or oral hyperosmotic)—one that is not used chronically—is administered. The IOP spike is rechecked to ensure that it has been controlled. Topical prednisolone 1% four times daily is prescribed for 7 days, and the patient is reviewed after 1 week. If anterior uveitis is present at 1 week, topical corticosteroids are continued.

Retreatment

The chance of success with a repeat procedure is considerably less than with an initial procedure, and the overall effect seems to wane considerably with time.

COMPLICATIONS

In one study, approximately 3% of patients (10 of 300 eyes) affected by primary open-angle glaucoma sustained a persistent elevation of at least 5?mmHg after ALT, which did not return to normal prior to surgical intervention. [5] [6] Corneal burns, which occur rarely, typically heal within a few days. If active bleeding from the angle is noted during treatment, the goniolens is pressed against the cornea to increase IOP and provide hemostasis. If the bleeding vessel is visualized, the laser is applied directly, using a large spot size (100–200?µm). The most common risk is IOP spikes, but these may be limited effectively using apraclonidine or brimonidine.[7] Finally, encapsulated blebs after filtration surgery may be seen more frequently in eyes that have had ALT.

OUTCOME

A period of at least 4–6 weeks after ALT is required before the final result can be evaluated. In two long-term studies, ALT maintained IOP control in 67–80% of eyes for 1 year, in 35–50% for 5 years, and in 5–30% for 10 years (i.e., an attrition rate of 6–10% per year).[8] [9]

The Glaucoma Laser Trial

The Glaucoma Laser Trial, a multicenter, randomized clinical trial, was designed to assess the efficacy and safety of initial treatment for primary open-angle glaucoma using ALT versus standard topical medication. The Glaucoma Laser Trial authors concluded that initial ALT is at least as efficacious as initial treatment with topical medication.[10]

SELECTIVE LASER TRABECULOPLASTY

Because ALT is limited by a well-recognized loss of efficacy with time and a poor response to repeat application, another laser system was developed in 1998 by Latina et al.[11] This laser is a frequency-doubled neodymium:yttrium-aluminum-garnet (Nd:YAG) nonthermal laser that selectively targets only pigmented cells, without causing any apparent damage to the surrounding structures; in contrast, the argon laser results in thermal coagulation of angle structures ( Fig. 235-2 ).[12]

TREATMENT GUIDELINES

The selective laser has a relatively large 400?µm fixed spot size. The energy is adjusted from 0.8?mJ downward, depending on the tissue response. Ideally, blanching without bubble creation is the end point. The number of shots applied is about 25–50 over 180°, with 180–360° treated initially. The spots are almost confluent and span the entire angle width because of the large spot size ( Fig. 235-3 ). Pre- and postoperative care is similar to that of ALT.

EFFICACY

The effect of SLT on IOP reduction is similar to that seen with ALT[13] ( Table 235-2 ). The prospect of repeating treatment safely with additional IOP reduction offers great promise. Clinical validation of these issues in prospective clinical trials is under way.

PERIPHERAL IRIDECTOMY

INTRODUCTION AND HISTORICAL REVIEW

Von Graefe[14] introduced surgical iridectomy for glaucoma in 1857. In 1920, Curran recognized that iridectomy was effective for angle-closure but not for open-angle glaucoma.[13] In 1956,

 

1559

 

 

Figure 235-2 Selective laser trabeculoplasty versus argon laser trabeculoplasty treatment. (Courtesy of M. Berlin, MD.)

 

 

TABLE 235-2 — SELECTIVE LASER TRABECULOPLASTY (SLT) VERSUS ARGON LASER TRABECULOPLASTY (ALT): A PROSPECTIVE, RANDOMIZED CLINICAL TRIAL

Mean IOP (mmHg)

ALT

SLT

Baseline

22.5

22.8

1 month

19.5

20.1

6 months

17.7

17.8

(From Damji KF, Shah KC, Rock WJ, et al. Selective laser trabeculoplasty argon laser trabeculoplasty: a prospective randomised clinical trial. Br J Ophthalmol. 1999; 83:718–22.)

IOP, Intraocular pressure.

 

 

Meyer-Schwickerath[15] demonstrated that an iridectomy could be created without the need for an incision, using xenon arc photocoagulation. This method failed to gain popularity, however, because of frequent lens and corneal opacities. Argon laser iridectomy and, more recently, Nd:YAG laser iridectomy have essentially replaced surgical iridectomy in the vast majority of cases.

PREOPERATIVE EVALUATION AND DIAGNOSTIC APPROACH

Laser iridectomy is the established procedure of choice for angle-closure glaucoma associated with pupillary block, whether primary or secondary or acute, intermittent, or chronic.

Indications

Laser iridectomy is indicated for the following types of glaucoma:

• Acute angle-closure.

• Chronic (creeping) angle-closure.

• Phacomorphic with an element of pupillary block.

• Iris bombé.

• Pigmentary dispersion syndrome (laser iridectomy for this indication remains controversial; the procedure changes the anatomy of the iris posterior bowing, but the long-term clinical advantage remains unproved).

• Prophylaxis of occludable angle (indicated for high-risk patients who are young, have a positive family history of angle closure, or need frequent dilated examinations, such as those with diabetes).

Laser iridectomy also aids in the diagnosis of aqueous misdirection (see Chapter 229 ) and plateau iris syndrome (in a nonpupillary-block narrow angle). In the former, a patent iridectomy is often needed before a diagnosis can be established.

Contraindications

Laser iridectomy is contraindicated in patients who are unable to sit and cooperate at the slit lamp and in eyes that have a

 

 

 

 

Figure 235-3 Human trabecular meshwork (organ system). A, Argon laser trabeculoplasty, 50?µm spot. B, Selective laser trabeculoplasty, 400?µm spot, 0.8?mJ/pulse.

cloudy cornea, widely dilated pupil, and flat anterior chamber with iridocorneal touch.

GENERAL TECHNIQUES

Argon versus Nd:YAG Laser

Both lasers are effective for the creation of iridectomies. The argon laser requires uptake of light energy by the pigment (thermal effect), but the Nd:YAG laser does not and works well on all iris colors (photodisruptive effect). The authors prefer the Nd:YAG because it is quicker, requires less energy to create a patent peripheral iridectomy, and is associated with fewer late closures than the argon laser is.[16] [17]

The Nd:YAG laser, however, does not coagulate tissue, and small hemorrhages occur more frequently with this modality. Therefore, in eyes that have prominent unavoidable vessels or in patients affected by a bleeding diathesis, combined treatment is preferred, first with the argon laser (to ablate vessels in the area) and then with the Nd:YAG laser (to establish a patent peripheral iridectomy).

Patient Preparation

Once the patient’s informed consent has been obtained, a drop of pilocarpine 1% is instilled twice, 5 minutes apart; miosis helps to stretch and thin the iris. A drop of apraclonidine 0.5% or brimonidine 0.2% is used 30 minutes preoperatively to

 

1560

prevent a postoperative IOP elevation. (Proparacaine 0.5% drops are instilled immediately before the procedure, in both the treated eye and the contralateral eye, to reduce blinking, which may disrupt treatment.)

Lens Choice

Two special therapeutic contact lenses limit eye movements and blinking, concentrate the energy delivered, magnify the target site, and act as a heat sink to minimize the risk of superficial corneal epithelial burns. The Abraham lens has a 66D planoconvex button. The Wise lens has a 103D planoconvex button,[18] which concentrates the laser energy more than the Abraham lens does because it minimizes the spot and magnifies the target even more; however, because of the higher power of the Wise lens, it is more difficult to focus. The other advantage of the Abraham lens is that energy delivered to both cornea and retina is four times less than that delivered to these tissues by the Wise lens.

SPECIFIC TECHNIQUES

The iridectomy is placed in the peripheral iris under the upper eyelid to avoid ghost images that may arise through the iris hole. Such ghost images may be accentuated by the tear meniscus. The 12 o’clock position is avoided when the argon laser is used, since bubble formation hinders further visualization of the target area. Iris crypts represent thinner iris segments and, as such, are penetrated more easily. The superonasal position (at 11 and 1 o’clock) is the best position to use to prevent inadvertent irradiation of the fovea, because it directs the laser beam farthest from the macula.

Argon Laser

Long pulses (0.2?sec) are used for light-colored irides (blue, hazel, light brown), and short pulses (0.02–0.05?sec) are used for dark brown irides. The rest of the treatment parameters are the same for both long and short pulses: a power of 1000?mW and a spot size of 50?µm ( Table 235-3 ).

A single area is treated with superimposed applications until perforation is obtained—that is, when a pigment flume is found to move forward (“smoke sign”) or, preferably, when the lens capsule is visualized through the patent iridectomy.

Nd:YAG Laser

The Q-switched mode is used, which allows treatment independent of pigmentation. Iris blood vessels are avoided. The iridectomy spot may be placed anywhere between the 11 and 1 o’clock positions, since bubble formation is minimal. The red laser

 

TABLE 235-3 — PROTOCOLS FOR LASER TREATMENTS

 

 

Peripheral Iridectomy

 

 

 

Argon

 

 

 

Argon Laser Trabeculoplasty

Light Irides

Dark Irides

Yttrium–Aluminum–Garnet (YAG)

Argon Laser Iridoplasty

Spot size (µm)

50

50

50

Fixed

200–500

Spot duration (sec)

0.1

0.2

0.02–0.05

Fixed (nsec)

0.2–0.5

Power (mW)

200–800

1000

1000

3–8?mJ

200–400

Number of spots per quadrant

20–25

15–25

25–100

1–5 shots (each burst consists of 1–3 pulses)

4–10

Wavelength

Argon green

Argon green

Argon green

1064?nm

Argon green

Contact lens

Goldmann

Abraham

Wise

Abraham, Wise, or Lasag CGI

Goldmann

Anesthetic

Topical

Topical

Topical

Topical

Topical

Pretreat

Apraclonidine or brimonidine

Pilocarpine and apraclonidine or brimonidine

Pilocarpine and apraclonidine or brimonidine

Pilocarpine and apraclonidine or brimonidine

Pilocarpine

 

 

aiming beam is brought to a focus when the multiple beams are brought into a single spot, aimed through the center of the contact lens. In a thick iris, the red beams may be separated slightly if the focus is advanced forward toward the iris stroma to maximize the energy within the thick iris. The energy used is 3–8?mJ, there are 1–3 pulses per shot, and one or more shots are used as required for penetration (see Table 235-3 ).

Combined Technique

Both argon and Nd:YAG lasers can be used in sequential combination for dark brown irides or for patients who are on chronic anticoagulant therapy. First, the argon laser (short-pulse mode) is used to attenuate the iris to about one fourth the original thickness and to coagulate vessels in the area. Then the Nd:YAG laser is used, with the beam focused at the center of the crater; one or more bursts of 1–3 pulses at 3–6?mJ are used to complete the iridectomy.

Second Iridectomy

One patent iridectomy is almost always sufficient to relieve pupillary block. In rare instances in which the long-term patency of the opening is uncertain or in the presence of inflammatory (uveitic) pupillary block, a second iridectomy may be made at the same sitting.

COMPLICATIONS

Intraocular Pressure Spikes

Elevated IOP occurs in approximately one third of eyes after treatment with either laser,[19] but the use of apraclonidine 0.5% or brimonidine 0.2% significantly decreases this risk, except for people who are already on chronic apraclonidine treatment. In a double-masked study of apraclonidine versus placebo, an IOP spike of 10?mmHg (1.3?kPa) or greater occurred in 43% of placebo-treated eyes but in none of the eyes treated with apraclonidine.[20]

Laser-Induced Inflammation

Laser-treated eyes may suffer transient iritis because of breakdown of the aqueous-blood barrier. Occasionally, inflammation may be quite severe, and posterior synechiae may develop. Prednisolone drops four times daily for 4–7 days may be used postoperatively.

Iridectomy Failure

An iridectomy may fail because the opening created is too small or because perforation is not achieved, with a residual iris

 

1561

pigmented layer present. Theoretically, functional failure can be avoided with a peripheral iridectomy diameter of at least 50?µm; an iridectomy with a diameter of 100–200?µm is ideal.[21]

Diplopia

Diplopia, or “ghost images,” is an occasional complaint, especially when the peripheral iridectomy is placed in the horizontal meridians or it is not covered perfectly by the upper eyelid. In some patients, diplopia (alleviated when the lid is lifted away from the eye) may result despite an iridectomy that is well covered by the upper eyelid. This probably results from a prism effect created by the tear meniscus or the upper eyelid. Intolerable monocular diplopia may be resolved by placing a cosmetic contact lens, which blocks the light from the peripheral iridectomy but not the pupil.

Bleeding

Postlaser hyphema is not uncommon after use of the Nd:YAG laser and is generally minimal and self-limited. Brisk bleeding may be stopped by applying direct pressure to the cornea using the contact lens to tamponade the bleeding site temporarily.

Lens Opacities

The lens rarely may be damaged directly from laser irradiation or indirectly because of deficient nourishment of the lens. The latter happens when the aqueous takes a short-cut through the iridectomy and therefore has reduced contact with the lens capsule. Opacities that are directly laser induced tend to remain focal in the area of the peripheral iridectomy, away from the visual axis.

Corneal Injury

Focal laser damage to the epithelium, Descemet’s membrane, or endothelium occurs frequently but is usually transient. A shallow anterior chamber, preexisting corneal edema, or pathological conditions of the cornea (e.g., guttae) make corneal injury more likely.

Other Complications

Postlaser malignant glaucoma, retinal burns, and lens-induced uveitis are extremely rare but reported complications.

OUTCOME

The patient is ambulatory immediately without restrictions; prednisolone four times daily for 4–7 days and the discontinuation of miotics are recommended. Patients are seen at 1 hour, 1 week, and 4 weeks after the procedure. Corneal status, IOP, anterior chamber reaction, and patency of the iridectomy with direct visualization and transillumination are assessed at each visit. Gonioscopy is critical to determine whether the angle has deepened.

If the peripheral iridectomy remains patent after 4–6 weeks, the opening usually remains open unless an active inflammatory response (e.g., uveitis, neovascularization) is present.

LASER IRIDOPLASTY

Laser iridoplasty consists of the placement of a circumferential ring of nonpenetrating contraction burns at the far iris periphery, just inside the limbus, to contract the stroma and widen the angle.[22] Laser iridoplasty is performed by the application of evenly spaced (4–10 burns per quadrant), large (200–500?µm), long (0.2–0.5?sec), and low-powered (200–400?mW) burns at the far iris periphery through the central button of a goniolens (see Table 235-3 ).

Laser iridoplasty does not require a clear cornea for the placement of the spots, because the energy is relatively defocused anyway. Laser iridoplasty is indicated in cases of pre-ALT of narrow angle (to increase visibility of the angle anatomy), angle closure that is unresponsive to medical treatment and for which peripheral iridectomy cannot be performed because of corneal clouding, and plateau iris syndrome.

 

 

REFERENCES

 

1. Katz LJ. Argon laser trabeculoplasty. Annu Ophthalmic Laser Surg. 1992;1:103–10.

 

2. Wise JB, Witter SL. Argon laser therapy for open angle glaucoma. Arch Ophthalmol. 1979;97:319–22.

 

3. Bournias TE, Wang F, Javitt JC. Racial variation in outcomes of argon laser trabeculoplasty [abstract]. Invest Ophthalmol Vis Sci. 1997;38(Suppl).

 

4. Ritch R, Shields MB, Krupin T, eds. The glaucomas. St Louis: Mosby; 1996; 1564–8.

 

5. Schwartz AL, et al. J Glaucoma. 1993;2:329.

 

6. Schwartz AL, et al. Ophthalmology. 1987;88:203.

 

7. Barnes SD, Barnes JD, Dirks MS, et al. Comparison of brimonidine 0.2% to apraclonidine 1% for control of intraocular pressure spikes after argon laser trabeculoplasty [abstract]. Invest Ophthalmol Vis Sci. 1997;38(Suppl).

 

8. Shingleton BJ, Richter CU, Belcher CD, et al. Long-term efficacy of argon laser trabeculoplasty. Ophthalmology. 1987;94:1513–8.

 

9. Spaeth GL, Baez KA. Argon laser trabeculoplasty controls one third of progressive, uncontrolled, open angle glaucoma for 5 years. Arch Ophthalmol. 1992;110: 491–4.

 

10. Glaucoma Laser Trial Research Group. The Glaucoma Laser Trial (GLT) and Glaucoma Laser Trial Follow-up Study: 7. Results. Am J Ophthalmol. 1995;120: 718–31.

 

11. Latina MA, Sibayan SA, Shin DH, et al. Q-switched 532-nm Nd:YAG laser trabeculoplasty (selective laser trabeculoplasty). Ophthalmology. 1998;105:2082–90.

 

12. Kramer TR, Noecker RJ. Comparison of the morphologic changes after selective laser trabeculoplasty and argon laser trabeculoplasty in human eye bank eyes. Ophthalmology. 2001;108:773–9.

 

13. Damji KF, Shah KC, Rock WJ, et al. Selective laser trabeculoplasty v argon laser trabeculoplasty: a prospective randomised clinical trial. Br J Ophthalmol. 1999;83:718–22.

 

14. Von Graefe A. Uber die Iridectomie bei Glaucom und uber den glaucomatosen Process. Graefes Arch Clin Exp Ophthalmol. 1857;3(2):456–555.

 

15. Meyer-Schwickerath G. Erfahrungen mit der Lichtkoagulation der Netzhaut und der Iris. Doc Ophthalmol. 1956;10:91–131.

 

16. Del Priore LV, Robin AL, Pollack IP. Neodymium:YAG and argon laser iridotomy: long term follow-up in a prospective randomized clinical trial. Ophthalmology. 1988;95:1207–11.

 

17. Moster MR, Schwartz LW, Spaeth GL, et al. Laser iridectomy: a controlled study comparing argon and neodymium:YAG. Ophthalmology. 1986;93:20–4.

 

18. Wise JB, Munnerlyn CR, Erickson PJ. A high-efficiency laser iridotomy–sphincterotomy lens. Am J Ophthalmol. 1986;101:546–53.

 

19. Robin AL, Pollack IP. A comparison of neodymium:YAG and argon laser iridotomies. Ophthalmology. 1984;91:1011–6.

 

20. Robin AL, Pollack IP, deFaller JM. Effects of topical Alo 2145 (p-aminoclonidine hydrochloride) on the acute intraocular pressure rise after argon laser iridotomy. Arch Ophthalmol. 1987;105:1208–11.

 

21. Fleck BW. How large must an iridotomy be? Br J Ophthalmol. 1990, 74:583–8.

 

22. York K, Ritch R, Szmyd LJ. Argon laser peripheral iridoplasty indications, techniques and results [abstract]. Invest Ophthalmol Vis Sci. 1984;25(Suppl).

Advertisements

One comment on “Chapter 235 – Argon Laser Trabeculoplasty and Peripheral Iridectomy

  1. This is a very good and helpful website for me. Thank you for the posts

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: