Lisa S. Gamell, MD; Alexander Schneider, MD; Timothy Saunders, MD; and Joel S. Schuman, MD, FACS
More than 4 decades ago, surgical iridotomy was the best available procedure for eyes with acute angle-closure glaucoma. Since that time, advances in laser technology and laser surgical techniques have allowed laser peripheral iridotomy (LPI) to emerge as the mainstay of treatment for most types of angle-closure glaucoma. Many deserve credit for early work on laser techniques for iridotomy,1–5 but 2 major developments have contributed to the current application and efficacy of this method: the development of lasers with good optics, capable of delivering sufficient energy, and the development of a corneal contact lens with a plano-convex button, such as that developed by Robert Abraham (Figure 56-1) or that of James Wise, which improve energy delivery to the iris (Table 56-1).
In pupillary block, the most common type of angle-closure glaucoma, there is increased apposition of the iris to the lens at the pupillary border. This blocks the natural pathway of aqueous into the anterior chamber and out through the trabecular meshwork (TM). This causes peripheral anterior chamber shallowing and occlusion of the angle by the iris tissue and could ultimately lead to intraocular pressure (IOP) elevation. When this block occurs acutely, an acute angle-closure attack ensues. When the block is intermittent or gradual, IOP fluctuations may occur, leading to intermittent or chronic types of angle closure. In any of these scenarios, IOP elevation, posterior synechiae, and disc damage may occur.
By performing a laser iridotomy, a hole is created in the peripheral iris. This opening allows an alternate pathway for the flow of aqueous from the posterior chamber to the anterior chamber, bypassing the pupillary block. The equilibration of aqueous flow allows the iris to fall back into its natural position, no longer occluding angle structures. In many cases, as long as peripheral anterior synechiae (PAS) have not formed, LPI may be curative. This procedure can be performed safely, in the office, as an outpatient procedure. The proper indications and techniques will be described below. This is a procedure that all ophthalmologists should be able to perform, as acute angle-closure glaucoma is one of the few ophthalmic emergencies and swift, accurate diagnosis and treatment can be sight-saving.
INDICATIONS
While LPI is clearly indicated in acute angle closure glaucoma, there are several other situations where this procedure is beneficial as well. These settings include pupillary block with narrow, occludable angles, chronic angle-closure glaucoma, mixed mechanism glaucoma, imperforate surgical iridotomy, suspected malignant glaucoma, pupillary block after cataract surgery, prophylactic treatment of a fellow eye after an acute angle-closure attack, and nanophthalmos (Table 56-2).
Typically, acute angle-closure glaucoma is initially treated with medications to lower IOP. Ideally, the acute attack can be broken with medical therapy, and the laser iridotomy can be performed afterward when the eye is no longer acutely inflamed. In inflamed eyes, laser openings in the iris may close subsequently, necessitating a second treatment. If an iridotomy is attempted during an acute angle-closure attack, the argon laser is preferred because of the greater incidence of bleeding in these inflamed eyes. In eyes with a phacomorphic component, miotic agents should be used cautiously, as this may break the attack in some eyes, while causing a paradoxical reaction and worsening the attack in others. In the latter case, argon laser iridoplasty is very useful in breaking the attack.1
Figure 56-1. Abraham lens used for laser iridotomy. (Reprinted with permission from Ocular Instruments.)
Joel S. Schuman, MD, FACS
We tend to favor the Nd:YAG laser Abraham iridotomy lens, as it has a 66-D plano-convex button that is both larger and easier to focus through than either the argon laser or Abraham iridotomy lens. The argon Abraham lens also has a 66-D button, but the button is smaller than the Nd:YAG laser version. This is because the cone angle of the argon laser is smaller than that of the Nd:YAG laser. (The cone angle is the angle created by the laser beam coming together to focus into a spot, which is the waist, or narrowest point of the beam. The smaller the cone angle, the easier it is to focus the laser, as the waist of the beam is present for a greater distance in space. This is why focus is so critical with the Nd:YAG laser, as there is only a very small area where the waist of the beam is present.) Because of the larger cone angle of the Nd:YAG laser, the Abraham lens for this instrument requires a bigger button. While this enables use of the lens with the Nd:YAG laser, it also facilitates its use with the argon or diode lasers.
The Wise lens, with its 103-D button, minifies the spot and magnifies the target to a greater extent than the Abraham lens, which is an advantage, as it concentrates the laser energy more; however, because of the higher power of the button, focus is more difficult with the Wise lens than with the Abraham. Many surgeons prefer the Wise lens because of its optical properties, while others favor the Abraham for its ease of use.
The safety profile and convenience of LPI have made it the preferred technique for most cases of acute angle closure. Even if it is suspected that the angle is extensively involved with PAS, an LPI should be done initially rather than filtration surgery, and the IOP and angle should be assessed after treatment. In combined mechanism glaucoma, it eliminates the angle-closure component. In the past, we advocated surgical iridotomy (rather than medical therapy) to treat eyes with angle closure and eyes with suspected combined mechanism glaucoma. In fact, Paul Chandler had surgical peripheral iridotomy himself for the latter condition. Nowadays, LPI would be performed initially in most patients. Exceptions would be patients who could not cooperate at a slit lamp or with the procedure while awake. Examples might include patients with Alzheimer’s disease, other types of dementia, or developmental delay. In such cases where angle closure was suspected, an exam under anesthesia with a surgical peripheral iridotomy might be the optimal treatment.
TABLE 56-1. ADVANTAGES OF THERAPEUTIC CONTACT LENS USE IN THE PERFORMANCE OF A LASER IRIDOTOMY
| Lens creates concentration of energy at the iris level |
| Lens acts as heat sink, decreasing corneal epithelial and endothelial burns |
| Lens acts as speculum, keeping lids apart |
| Lens provides limited control of ocular movement |
| Lens provides magnification of target site |
TABLE 56-2. INDICATIONS FOR LASER PERIPHERAL IRIDOTOMY
| Pupillary block with angle closure |
| Pupillary block with narrow, occludable angle |
| Chronic angle-closure glaucoma |
| Combined-mechanism glaucoma |
| Imperforate surgical iridotomy |
| Suspected malignant glaucoma |
| Fellow eye in acute angle- closure glaucoma |
| Pupillary block after cataract operation |
| Nanophthalmos |
However, what about the eye with a narrow angle with normal IOP and no PAS identified on indentation gonioscopy? In the past, we would follow such patients with repetitive darkroom tests, and if the results were negative, no iridotomy would be performed. Currently, we recommend performing an LPI in such patients. The risk/benefit ratio of LPI is such that, if an experienced observer were concerned that an angle appeared occludable, LPI is recommended. In this context, one should treat the patient as one would wish to be treated. It is seldom in medicine that any procedure is without risk, and the art and science of medicine involve balancing the benefits and risk of the disease with those of the treatment. Nonetheless, in experienced hands, the benefits of performing an LPI as a prophylactic measure to prevent acute or chronic angle closure in at-risk eyes far outweighs the risks. The most common risks include postoperative IOP spikes, inflammation, and localized hemorrhage. These can usually be minimized by proper technique or managed medically in most cases. It is recommended with any laser procedure to check the IOP 1 hour after completion of the procedure, because the majority of postoperative IOP spikes occur during this time. There are few long-term risks or side effects of LPI that would be more devastating than if the patient did not have the procedure and went on to develop angle-closure glaucoma.
Figure 56-2. (A) Argon, (B) diode, and (C) Nd:YAG laser iridotomies. Note that iris pigment epithelium is intact up to the border of the argon and diode laser iridotomies, but is absent in the Nd:YAG laser iridotomy. This may account for the lower closure rate experienced with Nd:YAG laser iridotomy, as pigment migration and plugging accounts for most cases of closure.
In recent years, clear lens extraction has been studied as a first-line therapy for those with primary angle-closure glaucoma, in comparison to LPI. Deepening of the anterior chamber and widening of angles after cataract surgery is a commonly recognized phenomenon, and has been observed in clear lens extraction as well. One multicenter, randomized, controlled clinical trial showed that clear lens extraction for patients with IOP 30 mm Hg or greater had greater efficacy in lowering IOP and was more cost effective than LPI.6 However, this issue remains somewhat controversial. More studies are necessary prior to adopting this more expensive, invasive technique with more serious complications as a first-line therapy.
CONTRAINDICATIONS
In addition to the inability to position the patient at the slit lamp, one should also be concerned about the presence of various corneal diseases and of a totally flat anterior chamber with iridocorneal touch. Nevertheless, we would recommend that consideration always be given to trying LPI initially, at least in one circumscribed area. We have successfully performed LPI in patients with interstitial keratitis and with posterior crocodile shagreen, although some endothelial damage did occur in the latter condition.
TECHNIQUE OF LASER IRIDOTOMY
There are several techniques that have been used to penetrate the iris and perform the procedure. Our favored technique is described in the box “Technique of Laser Iridotomy” and involves the use of the neodymium:yttrium-aluminum-garnet (Nd:YAG) laser.
Time and experience have shown the value of photodisruption in LPI. While the argon (or diode) laser is a useful photocoagulator and may be used to thin the iris or coagulate blood vessels to prevent bleeding, the Nd:YAG laser is superior for the purpose of LPI. Iridotomies created with the Nd:YAG are both simpler to perform and longer lasting than those made by photocoagulation (Figure 56-2).2–4
Lisa S. Gamell, MD
The concept behind a laser iridotomy is straightforward. A hole is put in the iris to relieve relative or absolute pupillary block and thus relieve iris bombé and angle-closure glaucoma. The hole can be made with any number of laser sources but most commonly argon, diode, Nd:YAG, or a combination of argon or diode and Nd:YAG lasers are used.
With all techniques, miotics should be used to constrict the pupil and thin the target tissue, and antiglaucoma medications should be used to prevent a post-laser pressure spike. An iridotomy lens should be used. The Nd:YAG laser Abraham-type iridotomy lens is an excellent choice. The contact lens increases the power density at the target site and additionally gives limited control over ocular movement. While the argon laser can be used for iridotomies in light or dark eyes, the Nd:YAG laser used alone is best with lighter eyes. The combined argon or diode and Nd:YAG laser technique can be used in almost all situations, but is excellent for dark eyes and in special situations, such as angle closure attack eyes or pseudophakic pupillary block.
PRETREATMENT REGIMEN
- The vision and IOP are checked preoperatively.
- Pilocarpine 1% or 2% is given to cause pupillary constriction.
- Iopidine (apraclonidine) 0.5% or other alpha-agonist is given.
- About 30 minutes later, after pupillary constriction has occurred and the iris is immobile, the patient is seated at the laser, and a contact lens with methylcellulose is applied.
ARGON LASER TECHNIQUE
The technique with the argon laser, whether the long-pulse technique in the lighter eye or the short-pulse technique in the darker eye, is the same. The aiming beam is brought into focus at an appropriate spot on the iris surface temporally at either 3 or 9 o’clock, and the laser is fired with the shots superimposed until a pigment flume is seen coming forward (smoke signal). When the anterior lens capsule is visible in the aiming beam, the iridotomy is complete. Historically, 11 or 1 o’clock was chosen as the site for the LPI, but there may be a greater chance of postoperative dysphotopsia if the lid does not cover the LPI opening.1
Argon Parameters
Long-pulse technique (for blue, hazel, or light brown eyes)
Time: 0.2 s
Power: l000 mW
Spot size: 50 μm
Number of applications: 1 to 30
Short-pulse technique (for dark brown eyes)
Time: 0.02 to 0.05 s
Power: 500 to 1000 Mw
Spot size: 50 μm
Number of applications: 25 to 100
ND:YAG LASER TECHNIQUE
The iridotomy can be placed temporally, at 3 or 9 o’clock. As mentioned above, 11 or 1 o’clock was typically chosen as the site for the LPI, but there may be a greater chance of postoperative dysphotopsia if the lid does not cover the LPI opening.1
Try to avoid visible blood vessels. The spots of the aiming beam are brought into single, crisp focus aiming through the center of the contact lens button. The red aiming beams are then separated slightly, by advancing focus forward, to ensure focus into the iris stroma. The laser is fired; frequently, the iridotomy will be complete after the first burst. If not, sequential bursts are applied, taking care to avoid any injury to the anterior lens capsule.
Nd:YAG Parameters
Energy: 3 to 6 mJ
Number of applications: 1 to 10 bursts of 1 to 3 pulses per burst
ARGON/ND:YAG TECHNIQUE
The argon laser is used to thin the iris so that approximately 20% of the tissue remains. It is done in identical fashion to the argon technique mentioned above using the 0.02 to 0.05 s time settings. When this is accomplished, the laser is changed to the Nd:YAG mode, or the patient is moved to the Nd:YAG laser. The contact lens can usually be left in place and will not fall out. The Nd:YAG laser beam is then focused into the depth of the crater, and one shot will usually complete the iridotomy.
Argon/Nd:YAG Parameters
For dark brown eyes, pseudophakic eyes, patients on anticoagulant therapy.
Argon thinning of the iris:
Time: 0.02 to 0.05 s
Power: 500 to 1000 mW
Spot size: 50 μm
Number of applications: 5 to 25
Nd:YAG perforation of the iris:
Energy: 3 to 6 mJ
Number of applications: One or more bursts of 1 to 3 pulses per burst
POSTOPERATIVE MANAGEMENT
Following laser iridotomy, the IOP should be checked sometime during the first postoperative hour to be sure there is no IOP elevation. In one study, approximately 10% of treated eyes had significantly elevated IOP (> 8 mm Hg rise from baseline); however, hardly any eyes (7 of 734) required further medical intervention to reduce IOP.2 If the IOP is high and the optic nerve is at risk or has preexisting damage, the IOP may be checked the next day; aqueous suppressants are prescribed as needed. In general, if the postoperative IOP is normal, the patient is seen 1 week later. During the first postoperative week, prednisolone acetate 1% is typically prescribed 4 times a day for 4 days (or longer in eyes with exuberant inflammation). At the postoperative week 1 visit, gonioscopy is performed to assess the success in opening the drainage angle.
REFERENCES
1. Beckman H, Sugar HS. Laser iridectomy therapy of glaucoma. Arch Ophthalmol. 1973;90:453.
2. Jiang Y, Chang DS, Foster PJ, et al. Immediate changes in intraocular pressure after laser peripheral iridotomy in primary angle-closure suspects. Ophthalmology. 2012;119(2):283-288.
This is a modification of the techniques previously outlined in the Fourth Edition by C. Davis Belcher III, MD.
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