Laser Iridotomy and Peripheral Iridoplasty
Robert Ritch, M.D.
Jeffrey M. Liebmann, M.D.
From the Departments of Ophthalmology, The New York Eye and Ear Infirmary, New York, NY and New York Medical College, Valhalla, NY.
Running title: Ritch/Laser iridotomy and iridoplasty
Supported in part by the New York Glaucoma Research Foundation
Corresponding author: Robert Ritch, MD, Professor and Chief, Glaucoma Service, the New York Eye and Ear Infirmary, 310 East 14th Street, New York, NY 10003, Tel: 212-673-5140; FAX: 212-420-8743; e-mail: ritch@inx.net
HISTORICAL OVERVIEW
In 1916, Verhoeff and Bell[Verhoef, 1916 #1350] first focused sunlight on the iris and retina. In 1956, Meyer-Schwickerath[Meyer-Schwickerath, #1352] first reported the creation of a patent iridotomy using the xenon arc photocoagulator. Patent iridotomies were created in 1958 using high-intensity radiant energy from a copper-coated carbon arc.[McDonald, 1958 #1351] These and other[Hogan, 1960 #1353; Burns, 1965 #1354] early attempts at thermal iridotomy were characterized by a high rate of complications, such as lens opacity and inflammation.
The advent of laser technology enabled the use of monochromatic focused light. Iridotomy using the pulsed ruby laser required less energy than previous methods.[Beckman, 1971 #1355; Flocks, 1964 #1356; Perkins, 1973 #1358; Perkins, 1970 #1357; Zweng, 1970 #1361; Zweng, 1964 #1360] In 1973, Beckman and Sugar[Beckman, 1973 #1362] attempted unsuccessfully to use the neodymium laser in human irides.
The development of the continuous wave argon laser initiated the era of successful treatment of glaucoma. Successful argon laser iridotomy was achieved in rabbits by Khuri[Khuri, 1973 #1363] and in humans by Beckman and Sugar.[Beckman, 1973 #1362] Others soon reported successful iridotomy in eyes with angle-closure glaucoma.[Abraham, 1975 #1364; Pollack, 1976 #1365] Elimination of the difficulties associated with penetration of dark brown and blue irides led to virtually 100% success in penetration with this procedure and revolutionized the treatment of angle-closure glaucoma.[Ritch, 1983 #1366; Ritch, 1980 #1367; Ritch, 1982 #1368; Stetz, 1983 #1369; Hoskins, 1984 #1371; Pollack, 1984 #1370] By the early 1980s, argon laser iridotomy had replaced incisional surgical iridectomy as the procedure of choice for angle-closure glaucoma.[Abraham, 1977 #1378; Go, 1984 #1379; Harrad, 1985 #1380; Kramer, 1984 #661; Mishima, 1985 #1381; Podos, 1979 #1423; Pollack, 1980 #1424; Pollack,
1984 #1370; Quigley, 1979 #866; Ritch, 1979 #1050; Ritch, 1981 #686; Ritch, 1980 #1367; Ritch, 1989 #1427; Robin, 1982 #1429; Schwartz, 1978 #1445; Schwartz, 1979 #1444; Yamamoto, 1985 #1466; Yassur, 1979 #1467]
Many clinicians now use the neodymium:YAG (Nd:YAG) laser because of the relative simplicity of the procedure compared to the more subtle techniques necessary to produce an iridotomy with the argon laser.[Klapper, 1984 #1372; Latina, 1984 #1373; Moster, 1986 #1374; Schwartz, 1986 #1375; Tomey, 1987 #1376; Wishart, 1986 #1377] However, complications, particularly hyphema and inflammation, are more common and severe.
DIFFERENTIAL DIAGNOSIS OF ANGLE-CLOSURE GLAUCOMA
Determination of the specific pathophysiologic mechanism responsible for the angle closure is crucial in arriving at an accurate diagnosis and in planning appropriate therapy. It is not just differentiation of angle-closure from open-angle glaucoma that is important, but accuracy of diagnosis within the group of glaucomas characterized by angle-closure.
Angle-closure glaucoma is an anatomic disorder comprising a final common pathway of iris apposition to the trabecular meshwork resulting from various abnormal relationships of anterior segment structures. These in turn result from one or more abnormalities in the relative or absolute sizes or positions of anterior segment structures or posterior segment forces which alter anterior segment anatomy.[Ritch, 1995 #9836]
Angle-closure results from blockage of the meshwork by the iris, but the forces causing this blockage may be viewed as originating at four successive anatomic levels: the iris (pupillary block), the ciliary body (plateau iris), the lens (phacomorphic glaucoma), and posterior to the lens (malignant glaucoma).[Ritch, 1995 #9836] The more posterior the level at which the angle-closure occurs, the more complex is diagnosis and treatment, since each level may have a component of the mechanism peculiar to each of the levels preceding it. Understanding these mechanisms makes appropriate treatment in any particular case an exercise in deductive logic.
Indentation gonioscopy provides the advantage of a dynamic view of the anterior chamber angle and is mandatory when evaluating an angle for the presence of peripheral anterior synechiae (PAS) (Figures 1, 2).[Forbes, 1966 #140] When attempting to determine whether or not a narrow angle is occludable, gonioscopy should always be performed in a completely darkened room using the smallest square of slit-lamp illumination possible which will enable a view of the angle. The difference in the angle in light and dark conditions may be much greater than expected and can be demonstrated by ultrasound biomicroscopy (UBM) (Figure 3). UBM is extremely useful for explaining the nature of angle-closure and the rationale of treatment to patients who may be confused between open-angle and angle-closure glaucomas and different types of laser surgery.
Pupillary Block (Aqueous pressure)
In pupillary block, aqueous humor flow from the posterior chamber to the anterior chamber is limited by resistance to aqueous flow through the pupil by iridolenticular contact. This creates a relative pressure gradient between the two chambers, and forces the iris anteriorly, causing anterior iris bowing, narrowing of the angle, and acute or chronic angle-closure glaucoma (Figure 4). During indentation gonioscopy, pressure on the cornea forces aqueous into the angle, widening it to permit viewing over the iris convexity. Since only aqueous in the posterior chamber offers resistance, the angle opens easily (Figure 5). The anterior segment structures and their anatomic relationships appear otherwise normal.
Pupillary block may be either relative or absolute. Relative pupillary block typically occurs in hyperopic eyes, which have a shorter than average axial length, shallower anterior chamber, thicker lens, more anterior lens position, and smaller radius of corneal curvature.[Lowe, 1977 #106; Delmarcelle, 1976 #110; Tomlinson, 1973 #111; Lowe, 1973 #100; Lee, 1984 #114] In absolute pupillary block, posterior synechiae between the iris and lens are responsible. When pupillary block develops, the iris assumes a bombé configuration, creating an angle which is narrow throughout its approach (Figure 6). Relative pupillary block is the underlies approximately 90% angle-closure. The rest have one or more mechanisms other than or in addition to pupillary block. Some can be worsened by miotic therapy, particularly in patients with intumescent or anteriorly subluxated lenses or malignant glaucoma.
Laser iridotomy eliminates the pressure differential between the anterior and posterior chambers and relieves the iris convexity. This results in several changes in anterior segment anatomy. The iris assumes a flat or planar configuration and the iridocorneal angle widens. The region of iridolenticular contact actually increases, as aqueous flows through the iridectomy rather than the pupillary space (Figure 7).[Caronia, 1996 #10128]
Plateau Iris (Ciliary Body Pressure)
A large or anteriorly positioned ciliary body can maintain the iris root in proximity to the trabecular meshwork, creating a configuration known as plateau iris.[Tornquist, 1958 #195; Tornquist, 1958 #195; Pavlin, 1992 #240; Ritch, 1992 #1046; Wand, 1993 #3212; Ritch, 1992 #1046; Pavlin, 1992 #240] The anterior chamber is usually of medium depth and the iris surface slightly convex. On gonioscopy, the iris root angulates forward and then centrally. With indentation gonioscopy, the ciliary processes prevent posterior movement of the peripheral iris, resulting in a configuration in which the slit beam follows the curvature of the iris to its deepest point at the periphery of the lens where the ciliary processes begin, then rises again over the ciliary processes before dropping peripherally (S sign) (Figures 8,9). Greater force is needed to open the angle than in pupillary block because the ciliary processes must be displaced, and the angle does not open as widely.
Plateau iris syndrome refers to the development of angle-closure, either spontaneously or after pupillary dilation, in an eye with plateau iris configuration despite the presence of a patent iridectomy or iridotomy. Acute angle-closure glaucoma may develop.[Godel, 1968 #196; Lowe, 1968 #197; Lowe, 1981 #198; Wand, 1977 #199] The extent, or the "height" to which the plateau rises, determines whether or not the angle will close completely with a rise in IOP (complete plateau iris syndrome) or only partially without a rise in IOP (incomplete plateau iris syndrome).[Lowe, 1989 #2841] The angle can narrow further with age due to enlargement of the lens, so that an angle with plateau configuration which does not close after iridotomy may do so some years later. Periodic gonioscopy is required. Argon laser peripheral iridoplasty (ALPI) is the definitive treatment for plateau iris.[Ritch, 1992 #1501]
Treatment must be targeted at the cause of angle-closure, in this case the ciliary body and iris root. If pupillary block is either not a component mechanism of the angle-closure or has been eliminated by iridotomy, it is necessary to find a way to eliminate the physical blockage of the angle. This is accomplished by ALPI, which compresses the iris root and creates a space where none was before.
Phacomorphic Glaucoma (Lens Pressure)
Lens swelling may convert a medium depth anterior chamber into a very shallow one and precipitate acute angle-closure glaucoma (phacomorphic glaucoma) from the lens forcing the iris and ciliary body anteriorly. Paradoxical reactions to pilocarpine treatment, which increases axial lens thickness and causes anterior lens movement, further shallowing the anterior chamber, are common.[Bleiman, 1979 #653; Abramson, 1973 #89; Abramson, 1974 #87; Gorin, 1966 #625; Rieser, 1972 #626] ALPI is effective in breaking attacks of phacomorphic angle-closure.[Ritch, 1982 #627]
The eye may be severely inflamed, as these patients are often referred after being treated unsuccessfully for a few days. Treatment must be oriented at the level of the lens. Lens removal is indicated for intumescent cataracts, but is prone to complications if performed during an acute angle-closure attack. Breaking the attack with ALPI allows two to three weeks for the inflammation and cornea to clear, permitting cataract extraction under conditions much closer to ideal.[Ritch, 1982 #627] Any element of pupillary block is treated as soon as possible (usually within two to three days) after breaking the attack.
In anterior lens subluxation due to trauma or such hereditary disorders as Weill-Marchesani syndrome, ALPI is less successful because the pressure of the lens against the iris continues, with or without an iridotomy, as long as the underlying cause is present. Cycloplegics are useful if the zonules are intact, but these may not always be so.[Ritch, 1992 #1673] A more complete discussion of this subject can be found elsewhere.[Liebmann, 1996 #10165; Ritch, 1996 #10166] If not treated in time, forward lens movement can lead to malignant glaucoma.
Malignant Glaucoma (Posterior segment pressure)
Also termed ciliary block or posterior aqueous misdirection, angle-closure caused by forces posterior to the lens which push the lens-iris diaphragm forward presents the greatest diagnostic and treatment challenge of the angle-closure glaucomas. Analogous to pupillary block, in which the angle is occluded by iris because of a pressure differential between the posterior and anterior chambers, in ciliary block, a pressure differential is created between the vitreous and aqueous compartments by aqueous misdirection into the vitreous (Figure 10).
Swelling or anterior rotation of the ciliary body with forward rotation of the lens-iris diaphragm and relaxation of the zonular apparatus causes anterior lens displacement. Ultrasound biomicroscopy often reveals a shallow supraciliary detachment not evident on routine B-scan examination (Figures 11, 12). This effusion appears to be the cause of the anterior rotation of the ciliary body and the forward movement of the lens-iris diaphragm. This, combined with aqueous misdirection into the vitreous, increases vitreous pressure, pushing the lens-iris diaphragm forward and causing angle-closure by physically pushing the iris against the trabecular meshwork in a manner similar to that in phacomorphic glaucoma.[Phelps, 1974 #643]
The effusions in many of these conditions, such as angle closure after PRP or scleral buckling, is self-limited, but treatment is indicated to prevent PAS formation and to lower IOP. A component of pupillary block is often present and the opposite angle often narrow, and if the cornea is clear, laser iridotomy can be performed. If appositional closure remains after iridotomy or if the cornea is not clear, ALPI again is almost always successful at opening the angle.
II. LASER IRIDOTOMY
A. Indications
1. Acute angle-closure glaucoma
Laser iridotomy is the procedure of choice for all angle-closure glaucomas with a component of pupillary block. All eyes with acute angle-closure glaucoma require laser iridotomy. Therapy can be assumed successful only when the angle can be determined to be open gonioscopically, as transient lowering of IOP may occur with medical therapy. Ideally, iridotomy should be performed after the acute attack has been terminated and the eye no longer inflamed. If this is not possible but the iris can be adequately visualized, iridotomy can be attempted, preferably with the argon laser because of the greater chance of iris bleeding with the Nd:YAG laser.[Fleck, 1991 #1476] Alternatively, pretreatment with the argon laser may allow safe application of the Nd:YAG laser with minimal bleeding. If an argon laser is not available and the Nd:YAG is to be used, an attempt should be made to perforate the iris with a single application, as bleeding at the iridotomy may preclude a second laser
application at that site. Acute angle-closure glaucoma which is unresponsive to medical treatment, or in which iridotomy is not possible due to hazy media, may be successfully aborted with ALPI (see below).[Ritch, 1982 #627; Ritch, 1989 #1427; Shin, 1982 #663]
Eyes with phacomorphic glaucoma usually have some element of pupillary block, but the response to treatment with miotics is often paradoxical, resulting in worsening of the attack.[Kramer, 1984 #661] Ciliary muscle contraction further loosens the zonules and causes lens thickening and anterior lens movement, further narrowing the angle. ALPI will almost always break the attack.[Tomey, 1992 #1510; Ritch, 1982 #627; Ritch, 1992 #1501]
Chronic Angle-closure Glaucoma
Eyes with chronic appositional closure with or without PAS are at risk for progressive synechial closure, trabecular damage, elevated IOP, and acute angle-closure. Iridotomy can eliminate the progression of PAS in eyes with chronic angle-closure caused by pupillary block. Even if the angle structures cannot be visualized by indentation gonioscopy prior to treatment (which may occur when IOP is over 40 mmHg), areas of functional meshwork may become apparent after iridotomy, particularly when there is "hamstringing" of the iris between PAS. In essence, all eyes with angle-closure should be given the benefit of iridotomy before filtration surgery is considered.
The effect of iridotomy on IOP control depends upon the degree of trabecular dysfunction. In eyes with minimal damage, iridotomy alone may reduce or control IOP. Failure of medications to control IOP prior to iridotomy does not necessarily mean that this will be so afterward. Quigley et al[Quigley, 1981 #1426] found reduced IOP in 44% of eyes with chronic angle-closure. After elimination of pupillary block by iridotomy, repeat gonioscopy may permit a more complete evaluation and assessment of the extent of trabecular injury and synechial closure.[Gieser, 1984 #685; Pollack, 1980 #1424; Ritch, 1980 #1367; Rivera, 1985 #265]
Aphakic or Pseudophakic Pupillary Block
Aphakic and pseudophakic pupillary block may be relieved by laser iridotomy.[Anderson, 1975 #1231; Cinotti, 1986 #1390; Forman, 1987 #1397; Patti, 1975 #1422; Samples, 1987 #1438; Werner, 1977 #1460] Loculation of pockets of both aqueous and vitreous may be present posterior to the iris, due to iridovitreal, iridocapsular, or iridolenticular adhesions. An iridotomy made over an area of vitreous-iris adhesion or apposition will not relieve the pupillary block[Anderson, 1975 #1231] Multiple iridotomies may be required before a pocket of aqueous humor is located and the block relieved.[Anderson, 1975 #1231; Ritch, 1980 #1367; Shrader, 1984 #1450; Melamed, 1988 #1490] In situations in which more than one loculated area is present, at least one iridotomy will be required for each area of loculation. Iridotomy helps to rule out pupillary block in cases of suspected malignant glaucoma, which requires disruption of the anterior hyaloid face or vitrectomy.[Epstein, 1984 #1395;
Shrader, 1984 #1450]
Prophylactic Iridotomy
With rare exceptions, prophylactic iridotomy should be performed in the fellow eye of a patient with either acute or chronic angle-closure glaucoma. Given similar refractive errors and globe size, the fellow eye of a high proportion of such individuals will eventually develop angle-closure. Angle-closure associated with an intumescent or anteriorly subluxated lens may present with an open, nonoccludable angle in the fellow eye. This may also occur in anisometropia, with angle-closure developing in the more hyperopic eye. Eyes with normal IOP and spontaneous appositional closure of at least one full quadrant on darkroom gonioscopy should also have prophylactic iridotomy.
In a retrospective study of 50 eyes treated with laser iridotomy or surgical iridectomy and 64 eyes treated medically to assess the long-term outcome of surgical and medical treatment of narrow angles, eyes receiving iridotomy or iridectomy showed a greater number of improved anterior chamber configurations (74% vs. 28%), had a lower incidence of PAS (2% vs. 10%) and required fewer antiglaucoma medications.[Schwartz, 1992 #1543] The overall percentage of eyes with increased IOP, decreased visual acuity, and abnormal visual fields were similar in the two groups.
Malignant Glaucoma
When acute angle-closure occurs on the basis of malignant glaucoma, medical treatment and/or iridotomy are usually insufficient to relieve the glaucoma. ALPI can open the angle, at least temporarily, and lower IOP. Prophylactic iridotomy usually protects the fellow eye against both acute angle-closure glaucoma and malignant glaucoma which could be triggered by opening and decompressing the globe. Pilocarpine, which increases lens thickness and shallows the anterior chamber, may trigger an episode of malignant glaucoma.[Cashwell, 1992 #1517; Merritt, 1977 #639]
To facilitate argon laser trabeculoplasty (ALT)
ALT may be difficult to perform in open but anatomically narrow angles. In these cases, iridotomy will facilitate the trabeculoplasty. If the angle is narrow on the basis of plateau iris, ALPI is a better alternative for improving visualization of the angle structures.
Nanophthalmos
Nanophthalmos, characterized by high hyperopia, short axial length, small corneal diameter, thick sclera, and narrow angles,[O'Grady, 1971 #8231] represents one end a spectrum of disease, and many hyperopic eyes have crowded anterior segments. Patients with nanophthalmos are anatomically predisposed to angle-closure glaucoma due to anterior chamber crowding. Angle-closure glaucoma usually appears between the ages of 20 and 50 years. Laser iridotomy is usually unsuccessful or only temporarily successful. Bilateral nonrhegmatogenous retinal detachments have been described following laser iridotomy[Karjalainen, 1986 #1408] and may be attributable to worsening of preexisting retinal or choroidal disease.[Singh, 1987 #1451]
Pigment dispersion syndrome
Laser iridotomy eliminates the iris concavity often found in pigment dispersion syndrome.[Potash, 1994 #1073; Pavlin, 1994 #3198; Lagreze, 1995 #10130] The concave iris configuration is due to reverse pupillary block, in which aqueous passing from the posterior to the anterior chamber cannot equilibrate because of extensive iridolenticular contact. The sudden increase of aqueous volume into the anterior chamber pushes the iris back against the zonular bundles. Iridotomy provides an additional pathway for aqueous equilibration between the chambers (Figure 13).
Contraindications
Iridotomy is contraindicated when angle-closure is caused by contraction of the iris against the trabecular meshwork, such as in uveitis, neovascular glaucoma or iridocorneal endothelial syndrome. It should not be performed in eyes with corneal edema or opacification precluding a view of the iris, or a grade 2 or 3 flat anterior chamber.
Techniques of Laser Iridotomy
Preoperative Preparation
Contact lenses reduce saccades and extraneous eye movements that can interfere with accurate superimposition of burns, keep the lids separated, focus the beam, and minimize reflective loss of laser power, while the gonioscopy solution absorbs excess heat, decreasing the chance of corneal burns.[Abraham, 1981 #1382; L'Esperance, 1975 #1415; Pollack, 1980 #1424; Ritch, 1983 #1366] The Abraham lens consists of a fundus contact lens with a +66 diopter planoconvex lens button on its anterior surface. This provides magnification without loss of depth of focus and reduces the effective size of a 50 µm spot on the iris surface to approximately 30 µm, providing higher energy per unit area and permitting the procedure to be performed with a lower total energy. The beam is rapidly defocused posterior to the site of focus, decreasing potential injury to the posterior segment.[Bongard, 1985 #1386; Schirmer, 1983 #1440] The Wise lens is similar but has a+ 103 diopter button, allowing even
greater concentration of laser energy.[Wise, 1986 #1463]
Topical anesthesia virtually always suffices. If the pupil is not already maximally miotic, 2% or 4% pilocarpine should be administered to minimize iris stromal thickness. Perioperative apraclonidine decreases the magnitude and frequency of postlaser IOP spikes,[Hill, 1991 #1525; Krupin, 1992 #1526; Robin, 1989 #1528; Robin, 1987 #1432] for which patients with more extensive synechial closure or trabecular dysfunction are at higher risk. The greater the energy used, the greater the risk of postoperative IOP spike.
Iris variations in thickness, color, and number and size of crypts should be taken into account (Figure 14). It is usually easier to perform iridotomy in the base of an iris crypt, where the stroma is thinner. An arcus senilis should be avoided because the density of the arcus causes a drop in laser power across the cornea, and the arcus itself interferes with clear focusing of the beam. This is less of a problem with the Nd:YAG laser than with the argon laser. The beam should be perpendicular to the contact lens surface to maximize energy delivery. Since focus is critical to efficient laser energy delivery, all lenses should be clean. Medium brown irides are generally the easiest to penetrate with the argon laser, the energy of which is readily absorbed by the iris pigment. Light blue and dark brown irides are more difficult.[Ritch, 1979 #1050; Rivera, 1985 #265] Lighter irides are more easily penetrated with the Nd:YAG laser than are darker, thicker irides.
The iridotomy should be made peripherally between 11:00 and 1:00, where it will be covered by the upper lid, to minimize glare and diplopia. If the iridotomy is bisected by either the lid or the tear meniscus, the patient may be bothered by glare or a "white line" in the superior visual field.[Murphy, 1991 #1493] The beam should be aimed to avoid accidental foveal injury; performing the iridotomy nasally eliminates this possibility.
Types of argon laser burns
Various types of burns, including contraction, penetrating, punch, and cleanup burns, and their uses in particular circumstances have been fully described elsewhere.100 Low power, large spot size, and long duration contraction burns (500 µm spot size, 0.5 second duration, and 200 to 400 mW power) compact the stroma at the site of the burn and (1) increase the density of iris stroma to facilitate laser energy absorption in blue or light brown irides, (2) create a "hump" on which penetrating burns are placed, and (3) perform ALPI or pupilloplasty. One should begin with 200 mW in brown irides and 300 mW in light ones and adjust the power as necessary. If bubbles or pigment release occur, the power should be reduced. In very light irides, a 200 µm spot size may be more effective.
Penetrating burns are higher-power, small spot size (50 µm) burns designed to vaporize iris tissue and create an opening. In the late 1970s and early 1980s, burns of 0.1-0.2 sec duration and 1000-2000 mW power were common. These produce charring and penetration failure in darkly pigmented irides, while lower power, shorter duration burns are more successful at penetrating the surface layer of the iris and densely pigmented stroma.[Ritch, 1982 #1368] Burns of 0.01 or 0.02 sec duration were formerly termed punch burns. The optimal power is 600-1200 mW and varies depending on the duration of the burn and the consistency and pigmentation of the iris. In many eyes, the iris surface layer has denser pigment than the stroma. Charring is minimal or absent when punch burns are used.
In most blue, hazel and light brown irides, burns of 0.05 second duration, 50 µm spot size, and 600-800 mW power can be used after initial contraction burns. Failure of tissue to vaporize with each laser application implies that laser energy is being applied without effect. A second site may need to be chosen or a Nd:YAG laser employed.
Shorter duration (0.01 or 0.02 sec) burns are optimal for use in dark irides, particularly in black and Asian patients, to avoid charring at the base of the iridotomy site.[Ritch, 1982 #1368; Yamamoto, 1982 #1465; Mandelkorn, 1981 #1418; Mishima, 1985 #1381; Ritch, 1984 #5269; Ritch, 1982 #5270; Yamamoto, 1983 #5271] Once the surface layer of fibroblasts and melanocytes has been penetrated and the stroma is being chipped away, the duration can be increased to 0.05 sec. Posterior synechiae may occur less frequently with short duration burns.[Mishima, 1985 #1381]
After the stroma has been eliminated, cleanup burns (about 200 mW power, 100-200 µm spot size, and 0.2 sec duration) are used to remove residual iris pigment epithelium without dislodging more pigment into the opening. If shock waves due to high energy absorption are created, pigment from surrounding areas will often move into the opening (landsliding).
Linear Evaporation
This technique, originally described by Wise,[Wise, 1985 #1461; Wise, 1987 #5268] uses the radial orientation of the dilator muscle to enlarge the iridotomy. Punch burns are used to make a straight-line incision in the iris, perpendicular to the dilator muscle. The incision should be about 500 µm long, full-thickness throughout its length, and only as wide as a single row of laser burns. When the stroma is fully incised, the dilator muscle assists in separating the pigment epithelium, reducing the amount of pigment epithelium which must be lased and creating a larger opening.
Drumhead technique
In this approach, developed in the 1970s,[Pollack, 1980 #1424] 6-8 burns of 0.2 sec, 200 mW, and 200 µm are placed in a circle around the site selected for penetration to thin the iris stroma in the center of the ring and make it more taut. Penetrating burns are then applied in the center of the ring.
Helpful hints
Improvisation and flexibility in technique and choice of laser settings for different types of irides are the keys to success. The entire procedure may require anywhere from 1 to 300 burns. It should be remembered that 200 applications of 0.02 sec duration and 600 mW power equals 10 applications of 0.2 sec duration and 1200 mW power, the latter settings often requiring 100-200 burns to penetrate a dark iris.
For any iridotomy, the first burn often serves as an indicator for the ease of the procedure. The desired result from the first burn is the appearance of a small hole with a darker base and dispersion of a small amount of debris into the anterior chamber. Bubble formation indicates stromal vaporization. One then continues to deliver burns until the stroma has been penetrated.
In the absence of stromal pigmentation, bubble formation and pigment release may be minimal. One clue to the gradual deepening of the iridotomy is a gradual darkening of the base. An orange reflex at the time of beam impact, most commonly seen in irides with little stromal pigmentation, signifies that one is nearing the pigment epithelium.
When the pigment epithelium is reached, denser bursts of fine pigment appear in the anterior chamber. A cloud of pigment mixed with aqueous often slowly balloons into the anterior chamber, indicating passage of aqueous from the posterior chamber. Simultaneously, the iris stroma floats backward and the peripheral anterior chamber deepens. This can be quite marked in eyes with greater degrees of relative pupillary block. After penetration, the iridotomy may be enlarged and pigment removed with cleanup burns. At completion, the lens capsule should be visible through the opening. Gonioscopy should be performed to assure that the angle is open.
Transillumination through the pupil or the iridotomy is not a reliable indicator of success in light irides, since it is possible to destroy pigment epithelium without penetrating the stroma. Once this happens, the overlying stroma cannot be penetrated except with a Nd:YAG laser, and the surgeon may mistakenly assume that the procedure has been successful.
Neodymium:YAG Laser Iridotomy
The Nd:YAG laser creates a plasma of free ions and electrons at the site of optical breakdown. This photodisruption releases shock waves that mechanically cause tissue rupture, as opposed to the thermal effect of the argon laser.[Prum, 1991 #1499; Goldberg, 1987 #4641] Iris color and density are much less important than with argon laser iridotomy. By the mid 1980s, several series had been published describing the easily obtained, successful results of Nd:YAG laser iridotomy.[Haut, 1986 #5273; Albuquerque, 1987 #5274; Rockwood, 1984 #5275; Schrems, 1987 #5276; Wand, 1988 #5277; Moster, 1986 #1374]
One should begin with a single pulse at approximately 1.5 to 3 mJ to assess the response of both the patient and the iris to the laser application. An increase in energy to 4 to 6 mJ is often sufficient to create a patent iridotomy with one to three additional applications. We prefer a linear incision technique using lower power burns, on the order of 1 mJ,[Wise, 1987 #5268; Wise, 1987 #1462] and never to use the multiple pulse mode. The importance of precise focus on the anterior iris stroma cannot be overemphasized; maximal photodisruption is obtained and the possibility of lens injury minimized.[Fernandez-Bahamonde, 1991 #4636] Since the anterior lens surface is further from the iris in the periphery, the chance of accidental lens injury is reduced by choosing a peripheral location.
Other Wavelengths
Combining argon laser to thin the iris stroma and coagulate blood vessels followed by Nd:YAG completion has been advocated as an approach which takes advantage of the photothermal effects of the first and easier penetration achieved via photodisruption of the latter.[Ho, 1992 #1482; Damerow, 1989 #4642; Zborowski-Gutman, 1988 #4643; Singh, 1987 #1451] The risk of hemorrhage is also reduced.[Goins, 1990 #1480] Iridotomies may also be successfully created with combined dye and argon,[Hitchings, 1985 #1404] diode,[Emoto, 1992 #1475; Schuman, 1990 #1507] krypton,[Yassur, 1986 #5267] and picosecond[Frangie, 1992 #4637; Oram, 1995 #10127] lasers.
Postoperative Management
The eye should be irrigated to remove excess methylcellulose and a drop of prednisolone applied. An additional drop of apraclonidine can be administered. The patient should be reassured that the visual blur will dissipate. We often suggest that the patient relax for a short period of time and then return in 60 to 90 minutes for a postlaser pressure check. If the IOP is lower, which is often the case due to the previously administered pilocarpine and apraclonidine, the patient is discharged and instructed to return for follow-up from 1 day to 1 week, depending upon the severity of pre-existing damage and the complexity of the angle-closure mechanisms. The pupil can be dilated at that time if desired. Although the follow-up schedule needs to be individualized, all patients should be evaluated four to six weeks postoperatively to determine continued patency of the iridotomy. If a postoperative IOP rise occurs, oral hyperosmotics usually suffice to control it. Rarely,
paracentesis may be required.
Histopathology
Initial changes in the iris near the iridotomy site include edema, necrosis, loss of melanocytes, the presence of pigment-laden macrophages, and irregular clumps of granules on the pigment epithelial surface.[Pollack, 1980 #1424; Pollack, 1976 #1365; Rodrigues, 1978 #1435] Histopathologic examination of Nd:YAG laser iridotomies reveals circumscribed holes with limited tissue alteration at the margin, compared with more extensive early edema and tissue destruction after argon laser iridotomy.[Rodrigues, 1985 #1434] Pigment debris accumulates in the trabecular meshwork and decreases with time.[Robin, 1982 #1433] The pigment granules initially are located in the extracellular and intracellular spaces and are phagocytosed by the trabecular cells. The pigment becomes more concentrated in the juxtacanalicular meshwork and is progressively absorbed. Histopathology of Nd:YAG laser iridotomy, obtained at the time of cataract surgery 3 to 5 years later, reveals the edges to contain
loosely arranged melanocytes, fibrocytes and vessels without evidence of pigment proliferation or scarring.[Tetsumoto, 1992 #1509] Inflammatory changes in the meshwork have been noted histologically after persistent pressure elevation following laser iridotomy.[Greenidge, 1984 #804] Any increase in tonographic outflow facility after iridotomy is probably related to relief of pupillary block and reversal of appositional angle-closure.[Pollack, 1980 #1424]
Postlaser iris configuration and anterior chamber depth
Increased peripheral chamber depth has been shown ultrasonographically.[Schrems, 1990 #4639] Central anterior chamber depth is unaffected.[Jacobs, 1979 #133] This has been confirmed with Scheimpflug photography,[Morsman, 1994 #5278] which also shows a decrease in iris convexity.[Jin, 1990 #1484] Iridolenticular contact increases following laser iridotomy.[Caronia, 1996 #10128] Any apparent deepening of the central anterior chamber may be the result of the postlaser use of cycloplegia and discontinuation of miotics and their respective effects on lens position.
Complications
Corneal Damage
Corneal edema may prevent achieving a patent iridotomy with either the argon or the Nd:YAG laser. Scattering of the beam diffuses the laser power and precise focusing on the iris may be impossible. Greater energy is usually necessary and may cause corneal damage. If the angle is closed, ALPI can usually open it and lower IOP, buying time until the cornea can clear. If ALPI has been performed, but corneal edema is persistent, pupilloplasty to peak the pupil may eliminate pupillary block.
The argon laser can cause epithelial and endothelial thermal burns. Both were far more common when settings of 0.1 and 0.2 second were used. These rarely occur with the use of lower energy burns. Epithelial coagulation and whitening are transient, but may interfere with the delivery of laser energy and make the creation of a patent iridotomy difficult. If this occurs, an attempt can be made to angle the beam around the burn to complete the iridotomy.[Cooper, 1981 #1392] It may be necessary to choose another location for the iridotomy or use a Nd:YAG laser. Stromal edema and striate keratopathy may also occur. If the anterior chamber is extremely shallow, corneal endothelial injury may develop rapidly. This may be circumvented by using contraction burns to deepen the chamber before the placement of punch burns or penetrating burns. When the anterior chamber is extremely shallow, the power should be reduced and applications not performed too rapidly.
Endothelial burns are generally dense white with sharp margins. They require more time for resolution and may result in focal endothelial cell loss. Although endothelial cell loss following argon laser iridotomy has not been statistically significant during follow-up periods of up to 1 year,[Wishart, 1986 #1464; Panek, 1988 #1496; Hirst, 1982 #1403; Smith, 1984 #1452; Thoming, 1987 #1456] an increase in mean cell size and cell loss associated with the use of greater laser powers has been reported.[Hong, 1983 #798] Although endothelial cell number after Nd:YAG iridotomy has been reported to be unchanged,[Schrems, 1986 #1441; Panek, 1991 #1497] focal loss occurs when photodisruption takes place less than 1 mm from the endothelium and at the site of treatment.[Panek, 1991 #1497; Meyer, 1984 #1421] The area of focal loss is reduced with the use of an Abraham lens.[Power, 1992 #1498] Damage to Descemet's membrane occurs when this distance is reduced to 0.1 mm. Progressive corneal
edema requiring penetrating keratoplasty has been reported following Nd:YAG[Wilhelmus, 1992 #1514] or argon[Jeng, 1991 #1483; Zabel, 1991 #1515; Kalnins, 1989 #4645; Schwartz, 1988 #1508] therapy. Risk factors appear to include preexisting guttata and excessive laser energy.[Jeng, 1991 #1483; Zabel, 1991 #1515]
Intraocular Pressure Elevations
Prior to apraclonidine, transient postlaser pressure spikes were common. A rise greater than 6 mmHg occurred in up to 40% of patients and to over 30 mmHg in as many as 30%.[Krupin, 1985 #1413; Pollack, 1984 #1425; Robin, 1984 #1430; Schwartz, 1986 #1375] Approximately two-thirds of patients had a maximal elevation in the first hour and one-third in the second.[Moster, 1986 #1374; Pollack, 1984 #1425] Rapid elevation to high levels occurred immediately after both argon and Nd:YAG iridotomies.[Henry, 1986 #1401; Krupin, 1985 #1413; Moster, 1986 #1374; Robin, 1986 #1428; Schrems, 1984 #1442; Taniguchi, 1987 #1454; Yamamoto, 1982 #1465] Perioperative apraclonidine decreases the duration and magnitude of the rise and most IOP elevations are mild and easily controlled.[Robin, 1987 #1432; Robin, 1989 #1528; Robin, 1987 #1432; Kitazawa, 1989 #1486; Hong, 1991 #4647; Brown, 1988 #706]
No significant difference in postoperative pressure rises has been found between the two types of lasers.[Robin, 1984 #1430] The elevation may be related to the amount of energy used, the degree of pigment dispersion, and the preoperative outflow facility. Eyes in which iridotomies are performed prophylactically may have a lower incidence of postoperative IOP spikes.[Yassur, 1979 #1467] Pre- and/or postlaser treatment with miotics, beta-blocking agents, carbonic anhydrase inhibitors, or oral hyperosmotic agents has also been reported to reduce the severity of the rise.[Brown, 1985 #1257; Schrems, 1984 #1442; Liu, 1987 #1416; Liu, 1987 #1416; Hsieh, 1992 #4646]
Closure of the iridotomy Site
Closure of a previously patent iridotomy may be immediate or delayed. Early closure is caused by occlusion of the opening by circulating debris or landsliding of the pigment epithelium surrounding the iridotomy site [Brainard, 1982 #1387; Ritch, 1980 #1367] and is typically visible immediately following the procedure or at the time of the first postoperative visit.
Delayed closure is usually caused by localized pigment proliferation occluding the opening. Pigment proliferation is more prominent after argon laser iridotomy[Ritch, 1980 #1367; Del Priore, 1988 #1472] and usually occurs within the first 6 to 12 weeks. As many as one third of patients have been reported to require retreatment. The iris opening after Nd:YAG laser iridotomy is more irregular, with less pigment dispersion, but retreatment may be necessary in about 9% of patients.[Schwartz, 1986 #1375] Closure is extremely common in patients with uveitis after either type of laser. Other causes of late failure include the development of a transparent, thin fibrous membrane occluding the opening and regeneration of iris pigment epithelium from the margins of the iridotomy. This characteristically grows in evenly from the margins of the iridotomy toward the center and does not come forward to occlude the portion of the opening through the stroma. Functional closure may occur with
the formation of posterior synechiae between the iridotomy site and the lens. Retreatment to open the iridotomy is easy. Argon laser iridotomies that repeatedly close may remain open after Nd:YAG treatment.[Gilbert, 1984 #1523]
Other complications
Blurred Vision: Patients routinely experience transient postlaser blurring of vision. Patients should be informed preoperatively that when the argon laser is used, retinal pigment bleaching limits vision for 20-30 minutes and makes everything appear red. Other factors which contribute to blurring include the use of methylcellulose, pigment dispersion, anterior segment inflammation, residual pilocarpine effect, or hyphema when the Nd:YAG laser has been used.
Pupillary Abnormalities: Slight contraction of the iris toward the site of iridotomy is common, generally minor, transient, and does not produce visual complaints. It is more prominent with the argon laser than with the Nd:YAG laser. The extent of the peaking is greater the closer the iridotomy is to the pupil, the lighter the iris, and the greater the total energy used.
Diplopia and Glare: These are uncommon given the small size of most iridotomies, but may develop or worsen if the iridotomy enlarges over time.[Sachs, 1984 #1437] Diplopia is more common if the iridotomy is placed nasally or temporally, but may occur anywhere if it is not covered by the upper lid. The sensation of a horizontal line in the upper visual field, occasionally accompanied by glare, is common. It occurs when the iridotomy is partially covered by the lid margin and is relieved when completely covered or completely exposed.[Murphy, 1991 #1493] There is also a "shutter effect" created by the lid crossing the iridotomy site during blinking. Patients often no longer notice it after a few months. Tinted soft contact lenses to ameliorate diplopia have been described.[Kublin, 1987 #1414] Opaque contact lenses to cover the iridotomy site may be used to reduce the amount of stray light entering through it.[Fresco, 1992 #4638]
Inflammation: Postlaser anterior segment inflammation is typical, usually mild, and ceases within several days. Breakdown of the blood-aqueous barrier has been demonstrated with both the argon and Nd:YAG lasers.[Sanders, 1983 #1439; Schrems, 1984 #1443] Topical corticosteroids are routinely prescribed for a few days.
Posterior synechiae may occur between the pupil and the lens or the iridotomy site and the lens.[Lederer, 1989 #1487] Their formation may be less common after Nd:YAG laser iridotomy,[Moster, 1986 #1374] can be minimized by postoperative topical steroids, minimizing the total energy applied, and by dilating the pupil at the time of the first postoperative visit if the iridotomy is patent and the angle is adequately open.
Hemorrhage: Bleeding is rare with the argon laser because the iris tissue undergoes thermal coagulation. However, hyphema may occur[Hodes, 1982 #1405] and may even occur days after the iridotomy, accompanied by increased IOP.[Rubin, 1984 #1436] Nd:YAG photodisruption does not coagulate iris vessels, and a small hemorrhage at the iridotomy site may occur in up to 50% of patients.[Dragon, 1985 #1394; McAllister, 1984 #1419; Pollack, 1984 #1425] Bleeding can occasionally be more substantial.[Gilbert, 1984 #1523] Gentle pressure on the eye with the contact lens may help control the bleeding. The argon laser may be used to coagulate bleeding vessels or may be used before the Nd:YAG laser to coagulate the iris vessels in the location of the anticipated Nd:YAG iridotomy. Iridotomy in eyes with rubeosis or uveitis should be performed with the argon laser.
Lens Opacities: Focal, nonprogressive, anterior subcapsular opacities may occur after both argon and Nd:YAG iridotomy in up to 45% of eyes.[Robin, 1984 #1430; Schwartz, 1986 #1375] However, no increased incidence of visual impairment from cataracts in patients having had laser iridotomy compared to the general population has been presented. The possibility that the permanently altered aqueous flow pattern may adversely affect lens physiology has not been either proven or disproven.
Although rare cases of capsular rupture with Nd:YAG iridotomy have been described,[Berger, 1989 #1469] the earlier widespread fear of acute onset of cataract after Nd:YAG iridotomy has not been substantiated. Limiting the use of the Nd:YAG laser to single burst mode, performing the iridotomy peripherally, and focusing on the anterior iris stroma minimize the chance of lens damage. These localized lens changes do not affect visual acuity. Small ruptures of the anterior lens capsule after Nd:YAG iridotomy have been documented histopathologically in patients undergoing subsequent intracapsular cataract extraction.[Welch, 1986 #1459] Animal studies suggest that fibrous proliferation covers the small anterior capsular breaks.[Gaasterland, 1985 #1398] Pitting of the anterior lens capsule by the Nd:YAG laser also occurs.[Welch, 1986 #1459]
Retinal Damage: The possibility of photocoagulation of the peripheral retina between the equator and the ora serrata, which usually occurs when an opening is being enlarged,[Quigley, 1981 #1426; Watts, 1971 #1458] is greatly reduced by the use of a contact lens.[Bongard, 1985 #1386; Wise, 1986 #1463] Inadvertent foveal photocoagulation has been reported,[Berger, 1984 #1385] and proper positioning of the laser beam is essential. Choroidal and retinal detachment[Corriveau, 1986 #1393] and nonrhegmatogenous retinal detachment in nanophthalmic eyes[Karjalainen, 1986 #1408] have also been reported. Microperforations of the retina may occur with the Nd:YAG laser if the beam is inadvertently focused to within 2 to 3 mm of the retina.[Jampol, 1983 #1407]
Miscellaneous complications: Sterile hypopyon,[Cooper, 1981 #1392; Shin, 1984 #1449; Cohen, 1984 #1391] cystoid macular edema,[Choplin, 1983 #1389] unexplained loss of central visual acuity,[Balkan, 1982 #1383] lens capsule rupture,[Fernandez-Bahamonde, 1991 #4636] pupillary pseudomembranes,[Geyer, 1991 #1479] phacoanaphylactic endophthalmitis,[Margo, 1992 #4648] and malignant (aqueous misdirection) glaucoma[Go, 1981 #1399; Aminlari, 1993 #1516; Cashwell, 1992 #1517; Brooks, 1989 #1470; Fourman, 1992 #1519; Robinson, 1990 #948; Geyer, 1990 #1520; Hodes, 1992 #4649] have been reported.
ARGON LASER PERIPHERAL IRIDOPLASTY (ALPI)
This is a simple and effective means of opening an appositionally closed angle in situations in which laser iridotomy either cannot be performed or does not physically eliminate appositional angle-closure because mechanisms other than pupillary block are present. Contraction burns (long duration, low power, and large spot size) placed in the extreme iris periphery withdraw the iris stroma from the angle and compress it, mechanically opening angle.[York, 1984 #4716; Ritch, 1982 #627; Ritch, 1983 #1366; Ritch, 1989 #1427; Ritch, 1992 #1501] ALPI is highly successful in reversing acute angle-closure glaucoma when medical treatment fails.[Ritch, 1982 #627; Lim, 1993 #4651] A technique for direct treatment of 360° of the peripheral iris through a gonioscopy lens, termed gonioplasty, served as the conceptual basis for the modern procedure.[Kimbrough, 1979 #1412] Although ALPI is simple to perform, important aspects of technique must be followed for a successful result.
Approach to Acute Angle-closure Glaucoma
Copious miotic treatment was, and still is, common in the treatment of acute angle-closure glaucoma. This, however, is undesirable for several reasons. When IOP is over 60 mmHg, the pupil becomes unresponsive to miotics because of ischemia and paralysis of the iris sphincter. Pilocarpine may paradoxically worsen the block.[Gorin, 1966 #625; Mapstone, 1974 #128; Rieser, 1972 #626; Ritch, 1982 #627] Miotics cause forward motion of the lens-iris diaphragm, and overtreatment can exacerbate acute angle-closure when it is due to block at the level of or behind the lens. The following is our approach to acute angle-closure glaucoma:[Kramer, 1984 #661]
1. Examine the affected eye and fellow eye, particularly noting central and peripheral anterior chamber depth, the shape of the peripheral iris, and the appearance on indentation gonioscopy.
2. Administer an oral hyperosmotic agent and, if desired, aqueous suppressants.
3. Place the patient supine. This permits the lens to fall backward to whatever extent possible when the hyperosmotic shrinks the vitreous. Remember that the vitreous volume is reduced only about 3%, but this 0.12 cc equals twice the volume of the posterior chamber and half the volume of the anterior chamber.
4. Reassess ocular findings after one hour. IOP is usually decreased, but the angle remains appositionally closed. One drop of 4% pilocarpine is given and the patient reexamined 30 minutes later.
a. If IOP is reduced and the angle is open, pupillary block or plateau iris or both are responsible for the angle-closure, and the patient may be treated medically with topical low-dose pilocarpine, beta-blockers and steroids until the eye quiets and laser iridotomy performed.
b. If IOP is unchanged or elevated and the angle remains closed, level 3 or 4 block should be suspected, further pilocarpine withheld, and the attack broken by ALPI.[Ritch, 1982 #627; Ritch, 1989 #662; Shin, 1982 #663]
We have performed ALPI in nearly 100 attacks of angle-closure glaucoma unresponsive to medical therapy, even after several days. All but one eye, which had total synechial closure, responded with at least transient normalization of IOP and opening of the angle. ALPI does not eliminate pupillary block and is not a substitute for laser iridotomy, which must be performed as soon as the eye is quiet. However, even in eyes with extensive synechial closure, IOP is lowered sufficiently for a few days for the inflammation to resolve. The alternative of prolonging a paradoxical reaction to medical therapy for several days seriously increases the possibility of irreversible damage to the iris, lens, cornea, trabecular meshwork, and optic nerve.
Up to one-third of angles without PAS remain narrow after iridotomy, and approximately half of these are capable of closure with mydriasis.[Lowe, 1964 #665] Continued appositional angle-closure in the presence of a patent iridotomy is an indication for ALPI.[Ritch, 1989 #1427; Ritch, 1992 #1501] If extensive PAS are present after ALPI, goniosynechialysis may be performed. This procedure is successful if the PAS have been present for less than one year.[Campbell, 1984 #670] Promising results have been reported in both phakic and pseudophakic eyes.[Ando, 1990 #1923; Nagata, 1985 #951; Tanihara, 1992 #2808] It is effective both alone and in conjunction with other surgical procedures.[Shingleton, 1990 #960] ALPI can be used postoperatively to further flatten the peripheral iris and prevent synechial reattachment.[Tanihara, 1991 #2807]
INDICATIONS FOR ALPI
Medically Unbreakable Attacks of Angle-closure Glaucoma
An attack of angle-closure glaucoma that is unresponsive to medical therapy outlined above and in which corneal edema, a shallow anterior chamber, or marked inflammation precludes laser iridotomy, or which is unresponsive to successful iridotomy, may be broken with ALPI.[Ritch, 1982 #627; Lim, 1993 #4651; Matai, 1987 #4650; Chew, 1991 #10148]
Circumferential treatment of the iris opens the angle in those areas in which there are no PAS. All published series have reported virtually 100% success. In a prospective study of 10 eyes with medically unbreakable attacks of 2-5 days duration, mean prelaser IOP was 54.9 mmHg and 2-4 hours postlaser was 18.9 mmHg.[Chew, 1991 #10148] Even when extensive PAS are present, the IOP is usually normalized within an hour or two, perhaps because of associated secretory hypotony. The effect lasts sufficiently long for the cornea and anterior chamber to clear so that, iridotomy can be performed. In cases in which an intumescent lens is responsible for the angle-closure attack, cataract extraction can be postponed until the intraocular inflammation has sufficiently resolved.
Plateau Iris Syndrome
In this condition, discussed above, the angle remains appositionally closed or occludable following laser iridotomy because of abnormally anteriorly positioned ciliary processes.[Pavlin, 1992 #240; Ritch, 1992 #1046]
Angle-Closure Related to Size or Position of the Lens
Angle-closure caused by an enlarged lens or pressure posterior to the lens (malignant glaucoma) is not often responsive to iridotomy, although iridotomy should be performed to eliminate any component of pupillary block. Appositional closure remaining after iridotomy can be partially or entirely eliminated by ALPI.[York, 1984 #4716; Ritch, 1989 #1427; Burton, 1988 #1471; Koster, 1990 #1930] After the angle has been opened and IOP reduced, cycloplegics may be given cautiously to ascertain the mechanism of the angle-closure.
Adjunct to Laser Trabeculoplasty
If a narrow but open angle results from plateau iris or angle-crowding, ALPI can retract the iris away from the trabecular meshwork.[Ritch, 1983 #1366]
Retinopathy of prematurity
Angle-closure in young children with retinopathy of prematurity occurs due to forward shifting of the lens-iris diaphragm.[Cohen, 1964 #8926; Hittner, 1979 #1894; Pollard, 1980 #5292; McCormick, 1971 #1898; Laws, 1994 #8928; Kushner, 1982 #1057] These children do not respond to iridotomy. In young adults with this condition, there appears to be a superimposed element of pupillary block, and iridotomy may be successful.[Ueda, 1988 #8927; Smith, 1984 #1899]
Nanophthalmos
Flattening of the peripheral iris by argon laser was first reported in 1979 by Kimbrough et al.[Kimbrough, 1979 #1412] Combined iridotomy and ALPI often brings the angle-closure under control.[Jin, 1990 #2759] Uveal effusions have been reported after both laser iridotomy[Karjalainen, 1986 #1408] and ALT.[Good, 1988 #2742] The risks of surgical intervention include malignant glaucoma, expulsive suprachoroidal hemorrhage, and retinal detachment.[Hyams, 1990 #8965] Posterior sclerotomy may or may not be successful at preventing uveal effusion.[Calhoun, 1975 #8047; Jin, 1990 #2759]
CONTRAINDICATIONS
Corneal edema is not a contraindication to ALPI when it is performed in order to break a medically unresponsive attack of angle-closure glaucoma. Extensive corneal opacification may present difficulties, because higher powers necessary to cause contraction of the iris may injure the cornea as well. Glycerin may help clear the cornea temporarily.
If the anterior chamber is flat with iris-corneal apposition, any attempt at photocoagulation will result in damage to the corneal endothelium. If the anterior chamber is very shallow, laser applications should be timed enough apart so that heat generated can dissipate.
Although ALPI has been reported to break PAS,[Wand, 1992 #1511] we have been unable to accomplish this. ALPI should not be used to relieve synechial angle closure, especially in eyes with uveitis, neovascular glaucoma, or iridocorneal-endothelial syndrome.
TECHNIQUE
ALPI is performed on an outpatient basis using topical anesthesia and an Abraham lens. Perioperative apraclonidine is administered. Shortly before treatment, 4% pilocarpine is applied topically to put maximal stretch on the iris. In eyes predisposed to a paradoxical reaction to pilocarpine, the risk is minimized by the timing of the pilocarpine. Miotics should not, however, be continued following the procedure.
Contraction burns (500 µm spot size, 0.5 second duration, and 200 to 400 mW power) are used to pull the surrounding iris tissue toward, and compact the stroma at the site of the burn (Figures 15, 16). The short-term effect appears to be related to heat shrinkage of collagen and the long-term effect secondary to contraction of a fibroblastic membrane in the region of the laser burn.[Sassani, 1993 #4718]
The aiming beam should be directed to the most peripheral portion of the iris possible. Spot placement short of the iris root is ineffective. The patient should look in the same direction as the quadrant of iris being treated. It is useful to allow a thin crescent of the aiming beam to overlap the sclera at the limbus. The surgeon should begin with 200 mW for dark irides and 300 mW for light ones and adjust the power as necessary to obtain visible stromal contraction. Contraction is accompanied by deepening of the peripheral anterior chamber at the site of the burn. If bubble formation occurs or if pigment is released, the power should be reduced. Occasionally, in light gray irides, a 200 µm spot size may be more effective.
Twenty to 24 spots are placed over 360°, leaving approximately 2 spot-diameters between each spot and avoiding large visible radial vessels if possible. Although rare, iris necrosis may occur if too many spots are placed too closely together. If this is insufficient, more spots may be given at a later time. The presence of an arcus senilis should be ignored. An extremely shallow anterior chamber and corneal edema, relative contraindications to laser iridotomy, do not preclude ALPI.
Other laser settings which have been advocated in the past, most commonly 200 µm, 0.l or 0.2 sec duration and 200 mW power, and burns placed through the angled mirror of a gonioscopy lens, often provide insufficient contraction and result in tissue vaporization. In those uncommon angles with a very sharp peripheral drop-off which do not respond well to the above treatment, one of the angled mirrors of a Goldmann or Ritch lens, a 200 µm spot size directly onto the peripheral iris can be used.
Gonioscopy should be performed to assess the effect of the procedure. Patients are treated with topical steroids four to six times daily for 3 to 5 days. IOP is monitored postoperatively as after any other anterior segment laser procedure and patients treated as necessary if a postlaser rise occurs.
Complications
Mild postoperative iritis is common and responds to topical steroid treatment. The patient may experience transient ocular irritation. Hemorrhage does not occur. A transient rise in IOP can occur as with other anterior segment laser procedures. Because ALPI is often performed on patients with extremely shallow peripheral anterior chambers, ill-defined, diffuse corneal endothelial burns may occur. We have seen only one case of corneal decompensation following ALPI in a patient with preexisting Fuchs' dystrophy. Lenticular opacification has not occurred and theoretically would be highly unlikely.
The duration of success depends on the mechanism of the cause of angle-closure. Eyes with plateau iris rarely if ever require retreatment. However, angle-closure may recur on the basis of lens enlargement with time. Pressure from the lens against the posterior iris may lead to gradual narrowing of the angle, possibly because of further anterior lens movement or to stretching of the iris stroma. Necessity for retreatment is most common in eyes in which angle-closure is due to forward lens movement, particularly malignant glaucoma. Patients in whom angle-closure results from intumescent lenses usually undergo cataract extraction. Patients should be observed gonioscopically at regular intervals and further treatment given if necessary.
Figures
Figure 1. Zeiss indentation gonioprism.
Figure 2. a. During gonioscopy with the Zeiss gonioprism, the cornea retains its normal configuration. b. During indentation, gentle pressure on the central cornea causes it to bow posteriorly, shallowing the central anterior chamber. The displaced aqueous is forced into the angle recess, open areas of appositional angle closure. Regions of synechial angle closure will remain closed.
Figure 3. a. Ultrasound biomicrograph of the anterior chamber angle in bright illumination. The cornea (C), iris (I), anterior chamber (AC), posterior chamber (PC), ciliary body (CB), lens capsule (LC), scleral spur (thin, black arrow), and Schwalbe's line (thick, black arrow) are visible. The iris is slightly convex (white arrow), consistent with relative pupillary block. Aqueous has access to the trabecular meshwork, which is between Schwalbe's line and sclera spur. b. In dim illumination, the peripheral iris has now moved against the trabecular meshwork, closing the angle.
Figure 4. Ultrasound biomicrograph of an eye with relative pupillary block. The iridocorneal angle is almost closed due to the iris convexity caused by increased pressure in the posterior chamber (PC). The ciliary sulcus (curved arrow) is normal. The arrowhead indicates the site of iridolenticular apposition. The trabecular meshwork is shown (straight arrow)
Figure 5. Goniophotograph of an appositionally closed angle in an eye with relative pupillary block (top). With gentle pressure during indentation gonioscopy, the angle opens uniformly, revealing the angle structures (bottom).
Figure 6. In more severely affected eyes, the iris convexity achieves a bombe configuration, as is present in this pseudophakic eye (I, iris; arrow, force of aqueous pressure).
Figure 7. a. Relative pupillary block angle closure prior to laser iridotomy. b. Following laser iridotomy, the iris assumes a flat configuration (white arrow) and the angle opens (black arrows at scleral spur and Schwalbe's line).
Figure 8. Typical gonioscopic appearance of plateau iris. a. Before indentation, the angle is closed to mid-trabecular meshwork. The iris assumes a characteristically flat approach to the angle. b. With indentation, the deepest displacement of the iris occurs at the lens equator. c. Diagram of an eye with plateau iris showing anterior extension of the ciliary processes, supporting the iris root against the trabecular meshwork.
Figure 9. Ultrasound biomicrograph of an eye with plateau iris which has already undergone laser iridotomy. The iris surface is flat and the chamber appears normally deep. The iris root is thick and the entire periphery of the iris is supported by large and anteriorly positioned ciliary processes.
Figure 10. In aqueous misdirection, an abnormality of the vitreociliary relationship causes a posterior diversion of aqueous into the vitreous (arrow). The resultant increased posterior segment pressure is the cause of angle-closure.
Figure 11. In some patients with a clinical diagnosis of malignant glaucoma, annular detachment of the ciliary body is the cause of the angle closure.
Figure 12. Ultrasound biomicrograph of an eye with malignant glaucoma. Anterior rotation of the ciliary processes (star) has forced the peripheral iris against the trabecular meshwork (arrowheads). A shallow supraciliary effusion is present (arrow)
Figure 13. a. In the untreated eye with pigment dispersion syndrome, the iris assumes a concave configuration (white arrow) due to pressure differential between the anterior and posterior chambers. b. Following laser iridotomy, elimination of the pressure gradient across the iris allows it to assume a planar, or flat, configuration.
Figure 14. Cross section of the iris. The anterior border layer, stroma, and pigment epithelium absorb argon laser energy differently because of differing pigmentation.
Figure 15. Correct placement of the ALPI burn in the extreme peripheral allows for contraction of the iris toward the burn and away from the angle.
Figure 16. a. Ultrasound biomicroscopic image of an eye with plateau iris prior to ALPI. b. A similar eye after ALPI. Note the compression of the iris root, creating a space between it and the trabecular meshwork.
References
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