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surgery.

Figure 40.4 Trabeculotomy under a fornix-based conjunctival and partial-thickness scleral flap. Preferred inferotemporal approach is shown, using a traction suture at the limbus to help hold the eye in adduction. A: Placement of trabeculotome into the cut end of Schlemm canal to the right. B: Rotation of the trabeculotome into the anterior chamber, tearing through the intervening trabecular meshwork. C: View of internal arm of trabeculotome tearing through trabecular meshwork as the instrument is rotated into the anterior chamber.

Postoperatively, patients are treated with topical antibiotics and steroids, together with low-dose pilocarpine for several weeks, as with goniotomy. Although hyphema occurs commonly after trabeculotomy, rarer complications include inadvertent filtering blebs, choroidal detachment, iridotomy, P.553

damage to the lens, creation of a false passage into the anterior chamber or suprachoroidal space, and infection (66, 67).

Figure 40.5 Trabeculotomy (360-degree modification using Prolene suture). Modification of trabeculotomy surgery (Fig. 40.4) in which the entire circumference of the Schlemm canal is cannulated with a 6-0 Prolene suture (blunted to have a small mushroom-shaped tip using disposable cautery) (A), and then both ends of the suture are pulled (B), resulting in 360-degree trabeculotomy.

One proposed modification of trabeculotomy involves the use of a Prolene suture (6-0 gauge and with a cautery-blunted tip) to perform a 180or 360-degree trabeculotomy at one surgery, using one or two external incisions into Schlemm canal (68, 69). The early results of 360-degree trabeculotomy are similar to those reported for more conventional trabeculotomy procedures (which usually affect 100 to 120 degrees of the angle described earlier) (Fig. 40.5).

Complete 360-degree trabeculotomy has also been recently performed by using the lighted Schlemm canal probe (ITrack 250 microcatheter, IScience Interventional, Menlo Park, CA), which was initially developed for use in canaloplasty (Fig. 40.6) (see Chapter 36). In this procedure, the catheter is threaded into one cut end of the Schlemm canal (usually made slightly larger with a small radial cut by using a Vannas scissor), and its lighted tip allows easy monitoring of its trajectory around the circumference of the Schlemm canal. One can also visualize the catheter if it attempts to leave the canal through a collector channel. Occasionally, the catheter can be redirected in these cases, although usually the best chance of complete cannulation occurs in these cases by withdrawing and then replacing the catheter through the opposite cut end of Schlemm canal in the opposite direction. Small amounts of viscoelastic material can also be injected through the catheter tip as it is advanced. Early experience suggests that this procedure may be as effective as 360-degree suture trabeculotomy, although increased postoperative hyphema has been reported (Freedman SF, unpublished data).

The effects of trabeculotomy should be determined about 1 month after surgery. Trabeculotomy (unless 360-degree suture trabeculotomy was performed) may be repeated in a different portion of the angle if inadequate effect was noted after the first procedure.

Combined Trabeculotomy-Trabeculectomy

If Schlemm canal has not been successfully cannulated or if similar trabeculotomy procedures have previously failed to control the IOP, the trabeculotomy can be combined with a trabeculectomy by removal of a full-thickness block of limbal tissue in the bed of the scleral flap, followed by peripheral iridectomy as in standard trabeculectomy. Some surgeons advocate combined trabeculotomytrabeculectomy as the first surgery for congenital glaucoma (70, 71 and 72), whereas others note that this procedure works better than angle surgery alone for primary congenital glaucoma with more severe clinical presentation (73). For this combined surgery, the surgeon chooses a conjunctival incision P.554

site according to his or her preferred trabeculectomy technique (see the following text), and may apply an antimetabolite, such as mitomycin C, to the sclera at the site of intended scleral flap formation before

dissection of the scleral flap (as described for adult trabeculectomy). If mitomycin C has been applied, it is advisable to ensure watertight closure of the Tenon and conjunctival layers with a vascular needle and absorbable suture, as for trabeculectomy (Chapter 38). Postoperative care should be as for pediatric trabeculectomy in this case (see Trabeculectomy). The mechanism of long-term pressure control in combined trabeculotomy-trabeculectomy (improved outflow of the trabecular-Schlemm canal pathway rather than filtration through the trabeculectomy site) has been debated, with no definitive agreement at this time.

Figure 40.6 Cleft in angle created by 360-degree trabeculotomy with IScience endoscopic Schlemm canal probe, in 5-year-old with pseudophakia and glaucoma. (An “X” marks the whitish cleft that runs circumferentially around the entire circumference of the angle.)

When the exact mechanism of the glaucoma is uncertain, such as with early-onset glaucoma in the Sturge-Weber syndrome (see Chapter 20), a combined trabeculotomy-trabeculectomy procedure may offer higher success rate than either procedure separately (74), although the risks associated with intraocular surgery in eyes with choroidal hemangioma make simple angle surgery preferred by some surgeons for this condition.

Goniotomy versus Trabeculotomy

Each of these procedures has staunch advocates who espouse the advantages of one technique over the other (75, 76, 77 and 78). Reported success has been similarly high with both procedures in favorable cases of glaucoma (e.g., previously unoperated eyes with primary congenital glaucoma, with postnatal onset in the 1st year of life) and primary congenital glaucoma with mild clinical presentation (73, 77, 79, 80). In a retrospective, comparative study by Mendicino, Beck, and colleagues, the success rate with 360-degree suture trabeculotomy was higher than that with goniotomy for primary congenital glaucoma (81).

If the cornea is clear, goniotomy has certain advantages over trabeculotomy: no conjunctival scarring, anatomic precision, less trauma to adjacent tissues, and shorter operating time. Reported success rates with goniotomy range from less than 80% to approximately 90%, although the procedure must be

repeated in about one half of cases (1, 79, 80).

The reported success rates with trabeculotomy are basically the same as with goniotomy, although fewer repeated procedures may be required, especially if the suture modification of trabeculotomy facilitates opening the Schlemm canal for 360 degrees in one operative session (68, 81). On the other hand, the microsurgeon experienced in adult glaucoma surgery may find trabeculotomy a more familiar procedure than goniotomy; moreover, trabeculotomy is not dependent on a clear cornea, and it can be converted directly to trabeculectomy if the Schlemm canal is not found or is inadequately cannulated (75, 76 and 77).

Peripheral Iridectomy

Several types of pupillary block glaucoma occur in children. Although uncommon, pupillary block glaucoma occurring after cataract surgery may respond to peripheral iridectomy (with or without vitrectomy or synechialysis) (82, 83). Glaucoma associated with advanced cicatricial retinopathy of prematurity may similarly improve with iridectomy alone or coupled with lens removal (84). In these cases, peripheral iridectomy should proceed essentially as described for adults (see Chapter 36). FILTERING SURGERY—TRABECULECTOMY

Filtering surgery is usually performed when goniotomy or trabeculotomy fails or— as is the case in some primary and many secondary glaucomas—is unlikely to succeed. This surgery should not be undertaken lightly in the child, as it removes permanently from use the child's native (albeit inadequately functioning) drainage system. Many such surgical procedures have been attempted over the years to treat children with glaucoma, including iridencleisis, cyclodiathermy, thermal sclerostomy (Scheie procedure), and standard trabeculectomy (1). Success rates were usually poor (in the 50% range, sometimes with multiple procedures), visual outcomes were limited, and rates of complication—which could include vitreous loss, scleral collapse, ectasia, retinal detachment, and endophthalmitis—were n ot insignificant (approximately 20%) (85, 86 and 87). Poor outcome from trabeculectomy is most likely multifactorial, with contributing factors including low scleral rigidity, exuberant healing response, and enlargement of glaucomatous eyes with thinning and distortion of intraocular anatomy. Adding to these physiologic considerations are the challenges of postoperative management in children; the long-term risks of infection and eye injury; and possible visual loss from nonglaucomatous causes, such as amblyopia. By contrast, several authors have recently reported much higher rates of success by using primary trabeculectomy in children with glaucoma, mostly in congenital cases (88, 89).

Intraoperative ß-irradiation to the surgical site, used in Britain, was associated with improved success of standard trabeculectomy in that country. In a retrospective series of 66 eyes (in patients younger than 18 years with congenital glaucoma), Miller and Rice reported successful pressure control (IOP <21 mm Hg) in roughly 40% of eyes after standard trabeculectomy, compared with greater than 65% after irradiation-augmented trabeculectomy. The authors found no complications attributable to the use of this low-dose ß-irradiation (90).

Although subconjunctival 5-fluorouracil (5-FU) has been administered postoperatively in children after trabeculectomy, resulting in successful filtration, its administration usually requires multiple sequential anesthesias and is limited by corneal epithelial toxicity, as in adults (91, 92).

The intraoperative use of mitomycin C has greatly enhanced the success of trabeculectomy in controlling glaucoma in adults at high risk for surgical failure (see Chapter 38) (93, 94), presumably by limiting postoperative scarring by Tenon capsule and scleral fibroblasts. The use of mitomycin C- augmented trabeculectomy in children with refractory glaucoma seems to have improved the ability to reduce IOP; however, this increased “success” carri es with it the sobering risks of late bleb infection (see later). Success rates vary from

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as high as 95% to much lower figures, some below 50% (92, 95, 96, 97, 98, 99, 100, 101, 102, 103 and 104). The reported success of mitomycin C-augmented trabeculectomy in children varies for numerous reasons, including differences in the method of defining and reporting success, the length of follow-up, the composition of the sample, and perhaps the surgical technique and postoperative management. Let

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us consider just a few of the more obvious examples. Mandal reported 95% success at last follow-up with this surgery in a group of mostly older patients with phakic eyes, although the duration of followup was fairly limited (95, 96); subsequent success more recently reported by the same surgeon fell to 65% at 18 months, this time assessed by performing Kaplan-Meier life-table analysis (105). In a retrospective study of 114 children with congenital or developmental glaucoma, with a mean age slightly younger than 6 years, Giampani and colleagues reported 5-year success of mitomycin C- augmented trabeculectomy to be 51%, with endophthalmitis developing in eight eyes (5%) (106).

The success of mitomycin C-augmented trabeculectomy in children is much higher in those who are older and phakic. Hence several authors independently found young age and aphakia to be associated with poorer outcomes (92, 101, 103). Mitomycin C application has included concentrations ranging from 0.2 to 0.5 mg/mL, applied from between 2 and 5 minutes (92, 95, 98, 99, 101, 102). To help titrate the postoperative filtration rate, Lynch and colleagues developed a probe tip (a modi fied Hoskins lens) for the diode laser (Iris Medical) that allows postoperative laser suture lysis of scleral flap sutures in the first 1 to 2 weeks after surgery during brief anesthesia (107). Others have used absorbable sutures (e.g., 10-0 Vicryl) or releasable sutures (see Chapter 38) in the trabeculectomy flap (Kenneth Nischal, MD, personal communication).

The response of very young children to mitomycin C-augmented trabeculectomy is extremely variable, with some patients scarring rapidly despite antifibrotic therapy and others developing hypotony with large avascular filtration blebs and even scleral ectasia. In addition to postoperative laser suture lysis and use of releasable scleral flap sutures, postoperative subconjunctival 5-FU may be used after trabeculectomy with mitomycin C to further retard healing and enhance filtration; this additional antifibrotic therapy did not enhance the success of mitomycin C-augmented trabeculectomy compared with other published series of similar cases (96, 98, 101).

Infants and children are subject to complications similar to those of adult patients. Hypotony, flat anterior chamber, choroidal detachment, decompression retinal and preretinal hemorrhages, and lens opacification have all been reported in pediatric cases (96, 97 and 98, 101). Most concerning, however, have been the cases of bleb-related infection, often associated with thin, avascular, and leaking blebs (Fig. 40.7), including cases of

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endophthalmitis with devastating visual loss in the operated eye (92, 100, 103, 106, 108, 109). Given the nontrivial incidence of bleb-related infection in adults several years after trabeculectomy augmented by the use of antiproliferative drugs (110, 111 and 112) (see Chapter 38), young children with filtering blebs must be watched very carefully for bleb leak and infection. Some glaucoma surgeons have tended toward alternatives to mitomycin C-augmented trabeculectomy in infants and very young children, partly on the basis of an assumed unacceptably high cumulative risk of bleb-related infection. An additional consideration regarding the exposure of a child's eye to mitomycin C relates to the potential long-term carcinogenic risk of using this potent alkylating agent (seen in rodents after systemic mitomycin C application) (113, 114). Because we do not know the long-term ocular sequelae of topical mitomycin C application to the sclera and Tenon capsule of young children with glaucoma, caution is advised in repeating mitomycin C filters in children with glaucoma. One must weigh the potential and as yet unknown long-term risks of mitomycin C use against those of other alternative procedures (discussed later).

Figure 40.7 Bleb infection in a long-standing avascular and intermittently leaking filtering bleb. A: Thin, avascular filtering bleb 5 years after mitomycin C-augmented trabeculectomy in a child with congenital glaucoma. The eye intermittently had hypotony and a flat anterior chamber after apparently minimal trauma. B: Brisk positive Seidel test associated with the leaking filtering bleb and flat anterior chamber described above in A. C: Hypopyon and fibrin plague on the lens capsule in association with endophthalmitis from an infected filtering bleb, 1 year after the leak shown in B. The child had an upper respiratory infection at the same time. The infection responded to vigorous topical and intravitreal antibiotics, and subsequently the bleb was removed and a Baerveldt implant placed, with preservation of preinfection vision and a clear lens.

Trabeculectomy surgeons have recently advocated use of a fornix-based conjunctival incision in adults (Chapter 38) and children, noting the decreased avascularity of the resultant blebs and their tendency to be more broad-based than with limbus incisions (Fig. 40.8) (115). The long-term differences in mitomycin C-augmented trabeculectomy success using the fornix-based rather than limbus-based incision for refractory pediatric cases await the test of time.

Posttrabeculectomy care of the pediatric patient includes careful long-term follow-up and the gradual tapering of topical steroid, with the prolonged use of nonsteroidal anti-inflammatory agents in selected cases, and the use of topical aqueous suppressants in others (e.g., when the bleb is relatively thin and seems to be enlarging gradually over time). Diligent parental awareness of the lifelong risk for bleb infection and leaks is imperative; for this reason, contact lens use in eyes with functioning trabeculectomy blebs is usually discouraged.

Figure 40.8 Partly avascular filtering bleb after mitomycin C trabeculectomy in an 8-year-old girl with late-recognized end-stage congenital glaucoma. Angle surgery and medications controlled the IOP for 6 years. Pressure is now below 10 mm Hg on no glaucoma medications.

Glaucoma Drainage-Device Surgery

Trabeculectomy, despite recent modifications and use of antiproliferative agents, still fails to control IOP (or is not applicable) in some cases of refractory pediatric glaucoma. Remaining surgical options include cyclodestructive and glaucoma (aqueous) drainage-device procedures. Given the low success with trabeculectomy in infants and in aphakic eyes (92, 98, 101), and the lifelong risk for bleb leak and infection in eyes with successfully filtering after trabeculectomy, glaucoma drainage-device surgery may be a reasonable option before trabeculectomy in selected patients (103, 109, 116) (Fig. 40.9). Glaucoma drainage devices have also proven useful in the treatment of uveitis-related glaucoma after failed angle surgery (117, 118, 119 and 120). Although the Molteno implant has been used in children for nearly 2 decades, experience has grown with other devices, including the Baerveldt and the Ahmed drainage implants. Reported success and complication rates vary widely (121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145 and 146). Numerous studies have reported on the success of Molteno drainage-device surgery for childhood glaucoma (131, 132 and 133, 135, 136, 137 and 138, 147, 148, 149, 150, 151, 152 and 153). Using a two-stage single-plate Molteno implantation procedure, Molteno and colleagues reported a 95% rate of success (defined as IOP <20 mm Hg) with a low complication rate (10%) in patients with advanced childhood glaucomas (133). In their series of 83 eyes, the average age at surgery was 11

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Shields > SECTION III - Management of Glaucoma >

41 - Cyclodestructive Surgery

Authors: Allingham, R. Rand

Title: Shields Textbook of Glaucoma, 6th Edition

Copyright © 2011 Lippincott Williams & Wilkins

> Table of Contents > SECTION III - Management of Glaucoma > 41 - Cyclodestructive Surgery 41

Cyclodestructive Surgery

The operations discussed in the preceding chapters lower the intraocular pressure (IOP) by improving the rate of aqueous outflow. This is clearly preferred from a physiologic standpoint, in that the aqueous humor can continue to be produced in an unaltered state and fulfill its various functions, including nourishment of intraocular tissues. An alternative approach to reducing IOP, however, is to decrease the rate of aqueous production by partially eliminating the function of the ciliary processes. Historically, these techniques were rarely the first operation of choice, because the results are hard to predict and the complication rate is high because of damage to adjacent ocular structures and the influence of a pronounced inflammatory response. Newer approaches with transscleral and endoscopic diode laser appear to be associated with reasonable efficacy and fewer vision-threatening complications and may be considered earlier in the treatment paradigm.

Cyclodestructive procedures constitute a valuable adjunct in our surgical armamentarium for eyes in which other operations have failed or when the surgeon wishes to avoid incisional surgery, such as in eyes with limited visual potential or with a high risk for intraocular complications with standard outflow procedures. An important exception is endoscopic cyclophotocoagulation (ECP), a procedure that may be a useful adjunct in eyes with reasonable visual potential and whose indications are still evolving. OVERVIEW OF CYCLODESTRUCTIVE PROCEDURES

Cyclodestructive operations differ according to (a) the destructive energy source and (b) the route by which the energy reaches the ciliary processes. In the 1930s and 1940s, several energy sources were evaluated, including diathermy, (ß-irradiation, and electrolysis, although only cyclodiathermy achieved clinical acceptance. Cryotherapy was introduced in the 1950s and became the most commonly used cyclodestructive procedure. However, subsequent experience with laser cyclophotocoagulation showed clear advantages over other techniques, and it has become the preferred cyclodestructive operation. Other cyclodestructive techniques include therapeutic ultrasonography and microwave cyclodestruction. Each of these energy sources may be delivered by the transscleral route, in which the destructive element passes through conjunctiva, sclera, and ciliary muscle before reaching the ciliary processes. Transscleral cyclodestructive operations have the advantages of being nonincisional and relatively quick and easy. However, significant disadvantages include the inability to visualize the processes being treated and damage to adjacent tissue, leading to unpredictable results and frequent complications. With the advent of laser energy as the cyclodestructive element, alternative delivery routes, including transpupillary and endoscopic approaches, are now possible.

EARLY CYCLODESTRUCTIVE PROCEDURES Penetrating Cyclodiathermy

Weve (1) introduced the concept of cyclodestructive surgery in 1933, using nonpenetrating diathermy to produce selective destruction of ciliary processes. Vogt (2, 3) modified the technique by using a diathermy probe, which penetrated the sclera, and this became the standard cyclodestructive procedure. One or two rows of diathermy lesions were generally placed 2.5 to 5 mm behind the limbus several millimeters apart for approximately 180 degrees. Early reports of experience with cyclodiathermy were encouraging (4, 5). However, subsequent study revealed a low success rate (about 5%) and a significant incidence of hypotony and phthisis (about 5%) (6).

Other Early Cyclodestructive Procedures ß-Irradiation Therapy

In 1948, Haik and coworkers (7) reported the experimental application of radium over the ciliary body in rabbit eyes and in one clinical case. Although this was shown to produce a reduction in the vascular supply of the ciliary body, it also caused damage to the lens, and the technique was never adopted for clinical use.

Cycloelectrolysis

Berens and coworkers (8) in 1949 described a technique that used low-frequency galvanic current to

create a chemical reaction within the ciliary body. This led to the formation of sodium hydroxide, which is caustic to the tissue of the ciliary body. Although this was shown in rabbit studies to produce destruction of ciliary processes (9), the procedure did not seem to have significant advantages over penetrating cyclodiathermy and never achieved widespread clinical popularity.

Therapeutic Ultrasonography

In 1964, Purnell and associates (10) introduced the concept of using focused transscleral ultrasonic radiation to produce localized destruction of the ciliary body in rabbit eyes. Coleman and coworkers in 1985 reported the results of rabbit studies and preliminary clinical trials with high-intensity focused P.566

ultrasound (11, 12). Several clinical trials of therapeutic ultrasonography in patients with refractory glaucomas, similar to those described in studies of other cyclodestructive procedures, have revealed IOP reduction to the low 20s (mm Hg) or less in one half to two thirds of the cases 6 to 12 months after a single treatment (13, 14 and 15). In a multicenter study involving 880 eyes, success (IOP between 6 and 22 mm Hg) after a single treatment was 48.7% at 6 months (16). With repeated treatments as required, the success rate rose to 79.3% at 1 year. The most common complication was an immediate postoperative IOP increase and mild iritis. Scleral thinning was observed in 2.5%, and phthisis in 1.1%. Decreased visual acuity occurred in approximately 20% of the cases.

Transscleral Microwave Cyclodestruction

The direct application of high-frequency electromagnetic radiation over the conjunctiva in rabbits produced heat-induced damage to the ciliary body with relative sparing of the conjunctiva and sclera (17). In rabbits with experimentally induced glaucoma, the procedure was successful in reducing IOP in all treated eyes for 4 weeks (18).

Excision of the Ciliary Body

In addition to the use of many cyclodestructive elements, as described earlier, other surgeons have sought to reduce aqueous production by removing a portion of the ciliary body. Several studies have revealed reasonable success and complication rates with this basic approach in eyes with unusually refractory glaucomas (19, 20 and 21).

LASER CYCLODESTRUCTION

Transscleral Cyclophotocoagulation

In 1961, Weekers and associates (22) used light as the cyclodestructive element, using the transscleral application of xenonarc photocoagulation over the ciliary body. As with other operations that use light energy, however, it was the introduction of the laser that eventually led to the clinical application of cyclophotocoagulation. In 1969, Vucicevic and associates (23) reported the use of a ruby laser to perform transscleral cyclophotocoagulation in rabbits, with an adjunctive cytochemical agent to enhance laser absorption by the ciliary body. Other reports of transscleral laser cyclophotocoagulation followed (24, 25 and 26), and in 1984 Beckman and Waeltermann (27) reported results of a 10-year experience with 241 eyes treated by using transscleral ruby laser cyclophotocoagulation. Their overall rate of IOP control was 62%, with 86% in aphakic eyes with glaucoma and 53% in eyes with neovascular glaucoma. Chronic hypotony occurred in 41 eyes, with phthisis in 17 cases, although most eyes retained their preoperative level of vision. However, it was not until the availability of specially designed Nd:YAG (neodymium:yttrium-aluminum-garnet) and, subsequently, semiconductor diode lasers that widespread interest in transscleral cyclophotocoagulation developed.

Figure 41.1 A: Semiconductor diode laser (IRIS, Oculight, SLx, Iris Medical Inc., Mountain View, CA) for transscleral diode cyclophotocoagulation. B: G-Probe handpiece for transscleral diode cyclophotocoagulation. (From Lin SC. Endoscopic and transscleral cyclophotocoagulation for the treatment of refractory glaucoma. J Glaucoma. 2008;17: 238-247.)

Instruments Nd:YAG Lasers

Nd:YAG lasers, with a wavelength of 1064 nm, have been useful for transscleral cyclophotocoagulation because they traverse the sclera with relatively low absorption and scatter. They may be operated in a pulsed, free-running, thermal mode, or a continuous-wave mode, and may be delivered by either a noncontact, slitlamp system, or a contact probe, fiberoptic system. However, these units do not appear to be commercially available for transscleral cyclophotocoagulation. (Readers wishing more information can consult the fifth edition of this book.)

Semiconductor Diode Lasers

Although semiconductor diode lasers, with a range of wavelengths between 750 and 850 nm, do not traverse the sclera as efficiently as Nd:YAG lasers do, they have the advantage of greater absorption by uveal melanin. In addition, they have the advantage of solid-state construction with compact size, low maintenance requirements, and no special requirement for electric outlet or water cooling.

The Oculight SLx (Iris Medical Instruments) is a continuouswave, contact delivery diode laser with a wavelength of 810 nm, a maximum power output of 2.5 to 3.0 W, and a maximum duration of 9.9 seconds (28, 29 and 30) (Fig. 41.1). The probe (G-Probe) consists of a 600-µm quartz fiberoptic, protruding 0.7 mm from a handpiece, which is fabricated to center the fiberoptic 1.2 mm behind the surgical limbus and parallel to the visual axis (30). The back of the G-Probe pushes the lid away from the surgical site, and the sides can be used to aid in spacing the laser applications (Fig. 41.2).

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