Ординатура / Офтальмология / Английские материалы / Atlas of Glaucoma, Second Edition_Choplin, Lundy_2007

Patient preparation

Apraclonidine (Iopidine®) or brimonidine (Alphagan®-P) preoperatively and postoperatively will limit pressure spikes and bleeding with iridectomies. The use of pilocarpine will tighten the iris and allow for more peripheral placement of the iridectomy, which

will decrease the possibility of postoperative glare symptoms. The operation should be performed in an area of iris normally covered by eyelid. Thin areas of iris such as crypts or transillumination defects in pigment dispersion (after pilocarpine use) are preferable locations.

Figure 16.14 Pupilloplasty. Pupilloplasty performed at a continuous-wave power too high and a duration too short. There has been pigment release and a partial, superficial effect.

iris tissue. Spots are placed in a circular fashion every 30 around the pupil and only the minimum number of spots needed to increase pupillary size over 2 mm are used. Lenticular opacities can occur. These tend to be more common in lighter-colored irides with poorer spatial confinement of the laser energy. The operator should be vigilant for eye motion as the laser energy is applied close to the pupil. If the duration of the burn is shortened and continu- ous-wave power increased, pigment release and a superficial partial effect will result (Figure 16.14).

Selected narrow angles may be widened by peripheral iridoplasty, particularly if the configuration is one of plateau iris and the narrowing is not due to pupillary block. In current practice, iridoplasty is performed by inducing a deep thermal contraction burn in iris stroma, causing mechanical retraction from the filtering angle by flattening of the peripheral iris contour (Figure 16.15). The laser parameters chosen to facilitate this type of laser–tissue interaction are long burns (0.5 s), large spot size (500 m), and low power (200–350 mW). If bubble formation occurs, the operator should stop energy application in mid-pulse and decrease continuous-wave power. The laser energy can be delivered through an Abraham contact lens to the most peripheral portion of the iris that is accessible. Six spots are placed per quadrant with 1000 m (two laser spot) spacing. In cases of plateau iris or nanophthalmos, the laser light may need to be delivered even more peripherally and a goniolens will facilitate this. In this case the spot size should be reduced to 200 m. In general, eyes with more chromophore (dark irides) will require less continuous-wave power than lighter irides. Iridoplasty is also a useful adjunct for cases that retain an appositional closure of the filtering angle after iridectomy or in cases where an iridectomy

power, long exposure laser treatments on peripheral iris contour.

cannot be initially created. Iridoplasty may also be useful to facilitate the performance of laser trabeculoplasty in eyes with a plateau iris configuration.

ARGON LASER TRABECULOPLASTY

Introduced originally by Wise and Witter, argon laser trabeculoplasty (ALT) is a frequently performed glaucoma procedure with good long-term follow-up. A variety of lasers have been used to perform trabeculoplasty. The most commonly used is the argon laser. In using this laser, operator macular photic stress may be reduced by using the argon green only rather than both the blue and green. In addition, the use of a contact lens with a metal halide coating will reduce the hazards of reflected light. The Ritch trabeculoplasty lens (Figure 16.16), has two different angles on its mirrors: 64 for the superior angle and 59 for the inferior angle. In addition, a planoconvex button is positioned over each mirror, which provides 1.4 magnification. This reduces a 50 m spot to 35 m and doubles irradiance. A standard oneor two-mirror lens without a planoconvex condensing lens has an angle of 62 and produces a 54 m spot from the original 50 m beam, which also slightly decreases irradiance (Figure 16.17). If a one-mirror lens is used, the patient is asked to move the eye in the direction of the treating mirror to accommodate the slight variance in filtering angle anatomy. Tilting the lens will introduce astigmatic error, creating an oval beam and altered irradiance (energy per surface area).

ALT is generally indicated for the reduction of intraocular pressure in patients with primary open-angle glaucoma, although it is also used to very good effect in patients with glaucoma associated with the pigment dispersion syndrome and

Figure 16.16 The Ritch lens. The Ritch lens has two different angles on its mirrors: 64 for the superior angle and 59 for the inferior angle. In addition, a planoconvex button is positioned over each mirror, which provides 1.4 magnification. This reduces a 50 m spot to 35 m and doubles irradiance. (Courtesy of Ocular Instruments.)

Figure 16.17 A standard oneor two-mirror lens. A standard oneor two-mirror lens without a planoconvex condensing lens has an angle of 62 and produces a 54 m spot from the original 50 m beam (magnification 0.93) which also slightly decreases irradiance. (Courtesy of Ocular Instruments.)

the exfoliation syndrome. It may also work in patients with steroid-induced glaucoma. Traditionally, it is used when the patient has reached maximum tolerated medical therapy, and in such cases usually does not allow the discontinuation of any of the medications being used. Recently, economic pressures have caused a renewed interest in laser trabeculoplasty as an alternative to increasing or allowing for a decrease in topical therapy. The procedure carries an initial success rate of 70–80%, but patients should be advised

that the effect may decrease over time; approximately 10% per year of eyes will return to pretreatment pressures. Re-treatment (after 360 of the angle has already been treated) carries only about a 30% chance of success, and consideration should be given to filtering surgery once AL has failed.

Preparation

Preoperatively and postoperatively, the patient is given apraclonidine (Iopidine®) or brimonidine (Alphagan®-P), unless an allergy dictates the use of another ocular hypotensive agent. Anesthesia is achieved with topical proparacaine. Viscous artificial tears solution such as Celluvisc® may be used with the laser lens to maximize patient comfort postoperatively.

Procedure

Standard parameters of a 50 m spot size and an exposure time of 0.1 s are usually employed. The suggested application site is the junction of the pigmented and non-pigmented trabecular meshwork. Application of laser energy at this position, easily found except in non-pigmented filtering angles, will further reduce the incidence of pressure spikes and peripheral anterior synechiae formation. This site can be found immediately below the termination of the parallel piped of light in a long thin slit beam under high magnification (Figure 16.18). The degree of pigmentation found in the trabecular meshwork and whether or not the treating lens increases irradiance will suggest to the operator what continuouswave power to select initially. In most filtering angles, 700 mW is sufficient. A general rule of thumb is to subtract 100 mW of power for each stepwise increase in trabecular pigmentation. Continuous-wave power should be sufficient to produce blanching or small bubble formation (Figure 16.19) at 0.1 s exposure time. Laser power meters may not be accurate and the surgeon should always believe the observed laser–tissue interaction over the power meter. The surgeon should also vary the power output for variations in angle pigmentation encountered intraoperatively. Treatment at too high an irradiance or posterior placement may lead to small focal peripheral anterior synechiae formation (Figure 16.20). Standard oneand two-mirror lenses as well as specialty lenses have been used for this procedure (Figures 16.16, 16.17). Before the treating lens is rotated, the operator should note angle landmarks to avoid overlapping a treated area. Finally, careful focusing is important for a uniform treatment. Focusing starts with adjusting the oculars of the laser to make the operator’s retina conjugate with the focal point of the laser. If the lens is tilted, irradiance is decreased and a larger area is irradiated.

Figure 16.20 Peripheral anterior synechiae formation after argon laser trabeculoplasty.

Also, if the spot size is increased by poor focus, the irradiance decreases by the square of the difference.

Treating the eye in divided sessions or limiting laser treatment spots to 50–60 will minimize chances of a postoperative laser-induced pressure spike. The operator should be consistent in the order of treatment, treating a total of 360 in two sessions (inferior then superior, nasal then temporal, right side then left side, etc.) or 360 with fewer laser spots in one session. Historically the former treatment technique affords a better treatment effect. In eyes with small central islands of remaining visual field, the operator may wish to further subdivide the sessions to minimize the chances of a laser-induced intraocular pressure spike.

Other lasers also used in ‘argon’ laser trabeculoplasty differ in their laser–tissue interactions from those of argon. The frequency doubled quasicontinuous wave (high-frequency repetition) Nd:YAG (532 nm) laser’s micropulses that make up each macropulse are at the thermal relaxation time of sclera. This probably decreases surface tissue denaturing and scatter, resulting in slightly deeper photon penetration. In addition, the slightly longer wavelength is slightly less well absorbed by melanin, allowing slightly deeper penetration. This will slightly decrease observed surface effects.

SELECTIVE LASER TRABECULOPLASTY

Developed by Mark Latina, selective laser trabeculoplasty (SLT) is another laser-based treatment of the trabecular meshwork that improves the outflow state of the eye in open-angle glaucoma. Unlike ALT, it does not produce macroscopic thermal injury in the filtering angle (Figure 16.21). This laser technique uses a Q-switched frequency doubled Nd:YAG laser (Coherent Selectra 7000 or Selectra II). The short pulse widths (3 ns) are under the thermal relaxation time for the collagen-based tissues of the filtering angle. The laser energy is spatially confined by cells containing pigment (melanin) creating fatal injury on a microscopic scale. The efficacy of this treatment is similar to that of ALT, except that the maximal effect is reached sooner and retreatment of ALT-treated eyes is possible with good effect.

Procedure

Apraclonidine (Iopidine®) or brimonidine (Alphagan®) is used preand postoperatively. A coated one-mirror or specialty lens is placed under topical anesthesia. Typically 270–360 are treated. The spot size is preset at 400 m and approximately 25 non-overlapping applications are placed per 90 treated (Figure 16.22). The total energies used per application are usually in the 0.7–1.3 mJ range. Small bubble formation is a useful end point for energy levels applied.

Postoperative care

The inflammatory response to SLT is less than with argon laser trabeculoplasty. Postoperative regimens among users polled varied from q.i.d steroids for 4 days to non-steroidals on a p.r.n. (discomfort) basis over concern of blunting the macrophage response to the treatment.

LASER SUTURE LYSIS

Postoperative care

On completion of trabeculoplasty, a final drop of apraclonidine is given to the patient. The intraocular pressure is checked at 1–2 hours post-treatment. Corticosteroids are started at q.i.d. frequency and, if a pressure spike did not occur, the patient is asked to return in 1 week to insure discontinuation of topical steroids. Non-steroidal anti-inflammatory agents are an alternative for known steroid responders. The risk of an IOP elevation of 10 mmHg after ALT with apraclonidine prophylaxis is small.

One of the most significant advances in filtration surgery, the selective cutting of sutures after trabeculectomy, has had a profound effect on decreasing immediate postoperative hypotony and its sequelae while maintaining the benefits of full-thickness surgery. The effective window for melting of sutures without antimetabolites is 0–21 days, with effectiveness falling rapidly after 14 days. The use of antimetabolites such as 5-fluorouracil extends this greatly and sutures can be melted with good effect up to 4–6 weeks postoperatively. The use of

Figure 16.22 Spot size of argon laser trabeculoplasty versus selective laser trabeculoplasty.

mitomycin C deserves special mention. This potent agent also suppresses aqueous production, and suture lysis should be undertaken with caution. In general, an increased interval to suture lysis will decrease the chances of hypotony and also decrease the effect. Suture lysis after the use of mitomycin C may even be attempted in the face of a failed filter with good results; the length of time after surgery that this may be effective is not known. There are some limits in that nylon sutures will depigment over time and will heat more slowly. Great care should be taken to avoid buttonhole formation during suture lysis after the use of mitomycin C. The technique requires the use of a continuous-wave argon or quasi-continuous wave laser (frequency doubled Nd:YAG; 532 nm), argon dye (610 nm), krypton (647.1 nm) or diode (810 nm) laser. In a postoperative eye with any blood or hemoglobin present in the subconjunctival space, the most useful lasers are those that can emit 610-nm laser light or in the red spectrum, such as krypton. This wavelength (610 nm) is poorly absorbed by hemoglobin and decreases the possibility of a conjunctival buttonhole. If hemoglobin is absent, there is some evidence that yellow (585 nm) or orange (610 nm) may limit conjunctival damage.

Figure 16.23 The Hoskins laser suture lysis lens. The Hoskins laser suture lysis lens has a 120 diopter lens providing 1.2 magnification. This decreases a 50 m spot to about 42 m in use. (Courtesy of Ocular Instruments.)

Patient evaluation and preparation

The number and the effect each scleral flap suture had at the time of surgery should be reviewed. Phenylephrine (2.5%) may be given to reduce congestion of the tissues before treatment. Three laser suture lysis lenses are in widest usage (Figures 16.23 to 16.25). All three lenses thin and blanch overlying tissues, allowing visualization of the sutures. All three lenses help hold the eyelid; the Hoskins and Ritch lenses have flanges for this purpose. The Hoskins and Mandelkorn laser suture lysis lenses provide magnification and smaller spot sizes which effectively increase irradiance. This should be taken into account when selecting continuous-wave power and exposure duration. Care should be taken in handling the Hoskins lens, as the neck is somewhat fragile.

Figure 16.24 The Ritch laser suture lysis lens. The Ritch laser suture lysis lens does not provide magnification. The notch is useful for holding the eyelid but slightly cuts down the viewing field. (Courtesy of Ocular Instruments.)

Figure 16.25 The Mandelkorn laser suture lysis lens. The Mandelkorn laser suture lysis lens provides 1.32 magnification decreasing a 50 m spot to 38 m and increasing irradiance at the level of the suture 1.7 . (Courtesy of Ocular Instruments.)

Procedure

Topical anesthetic agents are used. The patient is asked to look down and the iridectomy is used to locate the approximate area of the scleral flap. The continuous-wave power should start low (50 m; 0.05–0.1 s, 400 mW) with caution directly proportional to the relative potency of antimetabolite employed and amount of blood in the subconjunctival space. The laser spot should be focused on the suture to produce one long cut end which will lie flat (Figure 16.26). After successful lysis, the melted suture ends will retract; occasionally the suture

Figure 16.26 Laser suture lysis. The limbal sutures should be cut first. Premature lysis of the posterior corner sutures may cause profound hypotony.

blanches but does not retract. This indicates that sufficient tension in the suture to cause retraction does not exist, and that no extra filtration can be gained by pursuing this suture. The one suture per session rule should be observed, especially when mitomycin C has been used. Additional sutures may be cut after careful evaluation a few hours after the initial attempt. In emergency situations aqueous may be released from the paracentesis created at surgery to temporize. Complications are mainly limited to small conjunctival buttonholes from the laser and hypotony with or without buttonhole formation. These may be treated with patching and with or without aqueous suppressants as the clinical situation dictates. If antimetabolites have been used, the use of a McCalister contact lens (Figure 16.27) without patching may be used to help close the conjunctival defect. This lens provides tamponade and may be tolerated for 1–2 weeks if needed. The use of aqueous suppressants is also an option with this lens. Blebrelated endophthalmitis is a continuous concern in any patient with a thin filtering bleb. The status of the scleral flap sutures should always be ascertained. If there appears to be an impending suture extrusion, this should be stopped by segmenting the suture or rounding the end.

AB EXTERNO CYCLODESTRUCTIVE

PROCEDURES

Introduction

It has been over 60 years since Weve and Voght introduced diathermy and penetrating diathermy, respectively, as cyclodestructive techniques. Since then, electrolysis, beta-irradiation, cryotherapy, xenon arc, ultrasound, surgical excision and various visible and infrared lasers have been tried in an