Ординатура / Офтальмология / Английские материалы / Shields Textbook of Glaucoma, 6th edition_Allingham, Damji, Freedman_2010

27 - Principles of Medical Therapy and Management Page 215 of 267

role in the treatment of pediatric glaucoma, although neither drug has been approved by the FDA for use in children. Apraclonidine (Iopidine, 0.5%) can be useful and well tolerated in the setting of angle surgery to minimize intraoperative hyphema (see later under Goniotomy) and may have a short-term role for treating infants who cannot tolerate ß-blo ckers or who have had recent corneal transplantation (and in whom one therefore wishes to avoid topical carbonic anhydrase inhibitors). Wright and Freedman found an 8% incidence of side effects among 75 infants and children given apraclonidine, 0.5%, with lethargy reported in 3 children younger than 5 months of age (23).

Brimonidine (available as brimonidine, 0.2%, and Alphagan P, 0.10% and 0.15%) can be useful in reducing IOP in older children, but it must be used with extreme caution in younger children. Its use should be avoided altogether in infants and in small and underweight children, because of its propensity to cause severe systemic side effects. Topical brimonidine administration has caused bradycardia, hypotension, hypothermia, hypotonia, and apnea in infants, and severe somnolence in toddlers (24, 25 and 26), especially when combined with topical ß-bl ockers(27).

Brimonidine is rarely an appropriate first-line drug for children, except in selected older children with intolerance to ß-blockers and carbonic anhydrase in hibitors. It may, however, be useful adjunctive therapy in those patients needing additional IOP reduction (Table 40.1).

The combination of brimonidine, 0.2%, and timolol, 0.5%, Combigan, is a potent drug (see the preceding text) that should not be used in children with contraindication to either of the component ingredients.

Prostaglandins

The prostaglandin-type drugs can prove useful in some selected cases of pediatric glaucoma, although published data are limited, and none of these drugs has received FDA approval for pediatric use. Latanoprost (Xalatan) has been useful in selected cases of pediatric glaucoma, particularly in patients with juvenile open-angle glaucoma and some patients with aphakia and port-wine stain-associated glaucoma; no serious systemic side effects have been reported (28, 29, 30 and 31). Travoprost (Travatan) has recently been reported to be well tolerated and effective at IOP reduction in selected patients with pediatric glaucoma (32). The prostaglandin drugs do induce growth of eyelashes in pediatric patients (29, 30, 33) (Fig. 40.1); surface redness, periocular skin pigmentation, and iris darkening have all been noted as well ((30); Freedman SF, unpublished data). Caution is advised if these drugs are used in children with uveitis, or with aphakia or pseudophakia (although reports of cystoid macular edema in pediatric cases are lacking at this time).

Figure 40.1 Long and thick eyelashes in both eyes of an 11-year-old boy who has taken latanoprost for treatment of mild aphakic glaucoma.

Prostaglandin-like agents do not yet seem appropriate as first-line treatment for children, except perhaps for selected cases of juvenile open-angle glaucoma with special risk for ß- blocker use. These agents may play an important adjunctive role when IOP control is inadequate despite use of other medications already discussed (Table 40.1).

(Secondary pupillary block glaucoma)

III. Filtration Surgery

A. COMBINED TRABECULOTOMY-TRABECULECTOMY

1. When trabeculotomy cannot be completed (failure to cannulate Schlemm canal) 2. Failed previous angle surgery (<2 goniotomies and/or trabeculotomies)

B. TRABECULECTOMY (usually with intraoperative mitomycin C)

1.Any glaucoma in an eye with reasonable visual potential and unscarred conjunctiva after angle surgery has failed, with guaranteed faithful follow-up (not usually suggested for infants and aphakic eyes)

2.Low likelihood of success with angle surgery (would sometimes favor IIIA, above)

C.COMBINED CATARACT REMOVAL-TRABECULECTOMY (Not usually recommended)

IV. Glaucoma Drainage-Device (Tube Shunt) Surgery

A.Infants and aphakic eyes after failed angle surgery or if low likelihood of success

B.Failed trabeculectomy with intraoperative mitomycin C and reasonable visual potential

C.High risk for complications with filtration surgery (e.g., Sturge-Weber syndrome)

D.High risk for failure with trabeculectomy from scarring (e.g., after multiple conjunctival surgeries)

E.Consider simultaneous IPSILATERAL LATERAL RECTUS RECESSION (e.g., patient with exotropia and planned Baerveldt placement)

F.COMBINED CATARACT REMOVAL-GLAUCOMA DRAINAGE-DEVICE SURGERY

(Rare cases only [e.g., cataract and refractory glaucoma in older child with uveitic or traumatic glaucoma and quiet eye])

V. Cyclodestructive Procedures

A. TRANSSCLERAL CYCLOPHOTOCOAGULATION (Diode laser)

1.Failed angle surgery (or angle surgery not possible) and minimal visual potential

2.Failed trabeculectomy and/or glaucoma drainage-device surgery with poor central vision

3.IOP too high after glaucoma drainage-device surgery with encapsulation but not blockage

4.Anatomy precluding trabeculectomy or glaucoma drainage-device surgery (e.g., disorganized anterior segment after trauma, sclerocornea)

5.In patients who are gravely ill, or when follow-up and postoperative care cannot be assured, or general anesthesia with intubation poses life-threatening risk

6.High risk for complications with intraocular surgery (e.g., Sturge-Weber syndrome)

B. ENDOSCOPIC CYCLOPHOTOCOAGULATION (Diode laser)

1. May be considered for any patient in whom transscleral cycloablation would be reasonable, provided anatomy allows limbal or pars plana approach to ciliary processes (best in aphakic/pseudophakic eyes) 2. May be appropriate after transscleral cyclophotocoagulation has failed to reduce IOP

3. May be appropriate in cases needing cycloablation in whom risk of inflammation is high C. CYCLOCRYOTHERAPY

1.Usually not indicated, except where anatomic considerations make transscleral or endoscopic laser cyclophotocoagulation difficult or unlikely to succeed

2.Repeat therapy in selected quadrants after previous cyclocryotherapy

aRare outside of developing countries.

bShould be performed only by surgeons very comfortable with goniotomy, given unprotected lens. IOP, intraocular pressure.

With the aim of incising the uveal trabecular meshwork under direct visualization, goniotomy is the surgical procedure of choice in many cases of primary congenital glaucoma. Trabeculotomy ab externo (see the following text), an alternative procedure, is especially useful when corneal clouding prevents an optimal view of the angle structures by gonioscopy

Goniotomy

In 1893, the Italian ophthalmologist Carlo de Vincentiis described a new operation that attempted to open Schlemm canal by incising the angle tissues (without visualization of the angle) (34). Because of a high complication rate and poor results in adults with chronic open-angle glaucoma, this operation was initially abandoned. With the advantage of clinical gonioscopy, Otto Barkan modified the technique as an operation for primary congenital glaucoma in 1938, dubbing it “goniotomy” (Gk. gonio—angle and tomein—to cut) (35). This effective operation for c ongenital glaucoma dramatically improved the previously dismal prognosis for this condition (36). The technique for performing goniotomy has remained essentially unaltered for more than 50 years—a testament to the effectiveness and widespread use of this elegant, brief, conjunctival-sparing procedure as an initial intervention for primary congenital glaucoma (1). Although the aim of goniotomy is to open a route for aqueous humor to exit the anterior chamber into the Schlemm canal by removing obstructing tissue, the precise mechanism by which pressure reduction occurs remains obscure. Successful goniotomy does appear, however, to reduce the IOP by improving facility of aqueous outflow (37). Goniotomy enjoys its greatest success in the treatment of primary congenital glaucoma presenting between 3 and 12 months of

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age (1), but it may also be used in other primary developmental and secondary glaucomas, although with reduced success (1, 37) (Table 40.3). Examples of these other primary glaucomas include juvenile openangle glaucoma (38) and early-onset glaucomas associated with Sturge-Weber syndrome, neurofibromatosis, and Lowe syndrome. Several secondary glaucomas may respond favorably to goniotomy in some cases (7), including glaucoma complicating chronic anterior uveitis and selected cases of aphakic glaucoma presenting early after congenital cataract surgery (39, 40). Goniotomy has been advocated as a prophylactic procedure in congenital aniridia before glaucoma develops, but its use in this setting is particularly technically challenging (41, 42) (Table 40.3).

Table 40.3 Angle Surgery— Expected Beneficial Outcomes on Intraocular Pressure Control

Glaucoma secondary to neurofibromatosis

Acquired aniridic glaucoma

Glaucoma with ectropion uveae

Older child with open-angle glaucoma after cataract removal

a Preventive— see Table 40.2

Preoperative medications should ideally be used for several days before planned goniotomy to maximally reduce the IOP and clear the cornea. Medications often used include oral acetazolamide or topical dorzolamide, together with apraclonidine, 0.5%, and judicious use of a topical ß-blocker in selected cases. To produce miosis, pilocarpine, 1% or 2%, should be placed on the eye just before it undergoes surgery, to promote miosis and thereby aid in protecting the crystalline lens from injury during the procedure. Acetylcholine chloride 1:100 (e.g., Miochol) may be injected into the anterior chamber if necessary to promote further miosis. Apraclonidine, 0.5%, may be applied to the eye just before surgery and may help decrease intraoperative bleeding.

Table 40.4 Child-Specific Recommendations for Commonly Performed Surgical Procedures in Glaucoma

Goniotomy

1.Ensure adequate angle view: if corneal edema present, use aqueous suppressants before surgery, and topical sodium chloride, 5%, just prior to surgery; place goniotomy lens on mound of viscoelastic, tip microscope approximately 45 degrees from the vertical, tip child's head toward surgical side.

2.Stabilize globe and practice rotation: use locking forceps on Tenon insertion (usually 6 and 12 o'clock); use speculum with low profile, try globe rotation before entering eye.

3.Optimize wound entry: enter eye only one time using 25-gauge, 1.5-inch needle, making entry into peripheral cornea and parallel to iris; pass needle carefully over iris to engage anterior trabecular meshwork.

4.Perform effective trabecular meshwork incision: make incision superficial and into anterior trabecular meshwork, passing first one direction, then the other; assistant rotates globe while needle is not engaged in the meshwork.

5.Avoid injury to lens: constrict pupil with pilocarpine, 2%, before surgery; visualize tip of needle at all times and maintain plane parallel to iris for all movements.

6.Minimize bleeding: use apraclonidine, 0.5%, drops before incision; incise the trabecular meshwork only; remove the needle carefully over the iris and have assistant “relax” any pull on locking forceps at this time; prepare to push on entry site with forceps to minimize chamber collapse, refill with balanced salt and filtered air bubble; dissolvable 10-0 suture to close entry site securely.

Trabeculotomy

1.Optimize location: unless combined with trabeculectomy, place incision temporal or nasal and just above or below the horizontal to facilitate scleral flap and spare superior conjunctiva for possible later surgery.

2.Optimize incision and scleral flap: fornix-based conjunctival flap; triangular limbus-based scleral flap (thick enough to facilitate watertight closure); radial scratch incision to one side of base of flap (to allow a second cut-down, if needed).

3.Maximize chances of finding Schlemm canal: make radial incision gradually, watching for transverse fibers of canal, at sclerolimbal junction; watch for blood-aqueous reflux.

4.Minimize chance of false passage: confirm Schlemm canal location by passing a blunted 6-0 Prolene suture into the canal, either for 360-degree suture technique or to verify that suture remains parallel to limbus (not in anterior chamber or suprachoroidal space); four-mirror gonioprism can sometimes visualize suture in the canal; place and rotate metal trabeculotome (if used) gently and under direct view to avoid tearing iris or stripping Descemet membrane.

5.Secure wound and minimize bleeding: fill chamber with viscoelastic before pulling suture for 360degree technique, and often after first trabeculotome pass before second pass in opposite direction; close scleral flap tightly with 10-0 Vicryl suture; close conjunctiva tightly with Vicryl suture.

Trabeculectomy (Usually with Mitomycin C)

1.Optimize exposure and stabilization: place 7-0 Vicryl suture into peripheral cornea in two places opposite intended surgery (e.g., at about 10:30 and 2:30 o'clock for superior site), to avoid corneal suture into thin cornea superiorly where view may be obstructed.

2.Optimize incision and future bleb morphology: fornix-based conjunctival flap for most cases, except where cornea compromised, thin superior limbus expected, or high risk with flat chamber (e.g., aniridia).

3.Use of antimetabolite: mitomycin C usually indicated (except in older children, in whom 5-FU may be used intraoperatively and postoperatively); apply to broad area of uncut sclera and Tenon capsule, but keep away from conjunctival edges and cornea, concentration usually 0.2 to 0.4 mg/mL for 2 to 5 min.

4.Scleral flap preparation, sclerostomy, and iridectomy: cut fairly thick flap with hinge at limbus; rectangular (approximately 4×4 mm); enter under fla p into cornea with supersharp blade (after paracentesis elsewhere); punch large (1×2 mm) anter iorly placed window; do not extend opening to edges of scleral flap hinge; make iridectomy; avoid ciliary processes if visualized.

5.Scleral flap closure: 10-0 nylon sutures at back corners of scleral flap; and two anterior releasable sutures buried into clear cornea (if feasible), titrated to adequate flow; buried knots.

6.Conjunctival closure and hypotony prevention: 8-0 Vicryl on vascular needle to close “ wings” of fornix-based incision, with two horizontal 10-0 Vicryl mattress sutures between; same suture to close both Tenon and conjunctival layers separately in limbus-based incision; avoid covering releasable corneal portion of scleral flap sutures; fill chamber and bleb first with balanced salt then with Healon if left “ leaky;” leave paracentesis for office refilling in older children.

Glaucoma Drainage-Device Surgery (Steps Specific to Children)

1.Choice of incision: best to make fornix incision unless scarring or abnormal anatomy precludes; winged limbal incision if necessary.

2.Choice of implant and location: size the device to the eye (e.g., S2 or FP-7 Ahmed requires axial length at least 21 mm or must either trim back of plate or place it closer to limbus; valved implant if

immediate pressure reduction needed, otherwise Baerveldt 250 mm2 in most cases; superotemporal quadrant usual best location; suture plate 7 to 8 mm from limbus with 8-0 nylon suture.

3.Consider lateral rectus recession for exotropia noted at time of device placement: avoids need for later dissection near bleb.

4.Optimize tube position and placement: tube into anterior chamber in most cases, parallel to iris and as far back as practical to prevent exposure and corneal-tube touch, almost parallel to superior limbus rather than toward central pupil; use 30-gauge “fin der” needle on viscoelastic before 23-gauge entry for tube; consider posterior chamber (over intraocular lens implant) or pars plana tube location in selected cases (need full vitrectomy if pars plana entry).

5.Wound closure and hypotony prevention: tube completely ligated (6-0 Vicryl) if nonvalved device; watertight closure (8-0 Vicryl running closure of both Tenon and conjunctiva if fornix incision vs. 8-0 Vicryl running closure of each wing, with “hood” on to cornea and central 10-0 Vicryl mattress sutures if limbal incision); chamber filled with viscoelastic unless tube ligated closed; optional venting slits in tubing for nonvalved device (made using 9-0 nylon needle).

6.Prophylaxis against the encapsulated bleb/high pressure phase: maintain anti-inflammatory treatment for several months (topical steroid then nonsteroidal agents) and use aqueous suppressants liberally to keep pressure low.

Cycloablation

1.Optimal type of ablation: transscleral vs. endoscopic laser initially vs. cryotherapy rarely.

2.Limit treatment with transscleral and endoscopic laser to three quadrants to help avoid hypotony, vs. two quadrants with cyclocryotherapy.

3.Minimize excess inflammation: use adequate anti-inflammatory treatment and consider short oral

steroid taper.

4.Minimize risk of phthisis: keep careful records of prior treatment, beware 360-degrees cumulative treatment.

5.Discuss limitations of treatment fully with parents to achieve mutual understanding of risks and alternatives.

Modified from Freedman SF, Johnston SC. Glaucoma in infancy and early childhood. In: Wilson ME, Saunders RA, Trivedi RH, eds. Pediatric Ophthalmology: Current Thought and a Practical Guide.

Springer; 2009.

Basic Technique

Goniotomy is performed by using a surgical goniolens and a goniotomy knife or needle (Table 40.4; Fig. 40.2) (43). There are several available types of goniolens, in addition to the round-domed Barkan goniolens, including the Lister modification, which includes irrigation, the Swan-Jacobs lens, which incorporates a handle, as well as the Hill goniolens and Khaw surgical goniolens, both of which allow the surgeon holding the lens also to fixate the globe. Numerous modifications of the Barkan goniotomy knife have been described, including attached fiber optics for intraocular illumination (44). A nontapered Swan knife (or needle-knife) enters the anterior chamber easily and cuts in either direction. Alternatively, a disposable 25-gauge needle attached to a syringe containing viscoelastic or Miochol may be used in place of a knife, allowing the

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anterior chamber to be deepened before incision and to be maintained on instrument removal (45, 46). The author prefers the latter method, using only enough viscoelastic to ensure chamber maintenance on needle withdrawal. Enthusiastic use of the viscoelastic may acutely increase corneal edema by increasing IOP, thereby degrading the surgeon's view of the angle structures.

Figure 40.2 Goniotomy from temporal side, shown using a Barkan goniotomy lens and 25-gauge needle used as the goniotomy knife. A: Incision in anterior trabecular meshwork, shown beginning from right to left. B: Correct location and depth of the goniotomy incision.

To perform goniotomy safely and effectively, corneal clarity must be sufficient to allow an adequate view of the angle structures. To this end, preoperative use of glaucoma medications and prompt application of sodium chloride, 5%, drops to the cornea under anesthesia may improve the angle view in borderline cases. Although corneal epithelial scraping has been described to facilitate an angle view for goniotomy, corneal stromal edema often persists after epithelial removal; in this setting trabeculotomy may be preferred (see Trabeculotomy). Alternatively, endoscopic visualization has been used for goniotomy in the setting of corneal opacification (47, 48 and 49).

Goniotomy surgery can be performed with a binocular head loupe, although the operating microscope provides better visualization (and affords the assistant a view of the angle) (50). The surgeon usually sits opposite to the portion of the angle to be operated (i.e., to the temporal side of the patient for nasal goniotomy), with the patient's head slightly rotated away from the surgeon. Moody or other locking fixation forceps may be placed on the superior and inferior rectus muscles when a nasal or temporal goniotomy is planned. Alternatively, the globe can be adequately held by applying the locking forceps nearer to the limbus, at the level of the Tenon insertion, with less likelihood of acutely worsening corneal edema. Viscoelastic may be placed onto the central cornea just before the operating goniolens is placed and may be helpful in preventing the formation of air bubbles between the goniolens and the cornea. The goniotomy lens may be stabilized with a nontoothed fine forceps in the positioning holes of the lens, or it may be modified to include a handle.

The goniotomy knife or needle is placed through peripheral clear cornea 1 mm from the limbus, opposite to the midpoint of the intended goniotomy, in a plane parallel to the iris. The knife or needle is guided over iris tissue (not pupil) to engage trabecular meshwork in its anterior third, just posterior to the Schwalbe line (Fig. 40.2A). A circumferential incision is then made for about 4 to 5 clock-hours (Fig. 40.2B), and the knife or needle is carefully and quickly withdrawn from the eye over iris tissue at all times. The incision should be superficial, with no grating or scraping sensation noted. A deeper cleft, with exposure of whiter tissue may be noted in the wake of the incision, with a widening of the angle, and a posterior movement of peripheral iris in some cases. The assistant may help the surgeon to extend the angle available to goniotomy by rotating the eye clockwise and counterclockwise at the surgeon's request. After knife (or needle) withdrawal, blood often egresses from the angle incision, stopping when the chamber is refilled with balanced salt solution; placing a sterile air bubble can assist in assessing the anterior chamber the next morning. A single suture of 10-0 Vicryl secures the corneal wound (37, 51). Postoperative treatment includes the use of topical antibiotic, steroid, and miotic agents. (Miotics are often omitted, however, in cases of uveitic glaucoma.) The baby's head should be kept elevated (a car seat works well for this), and the eye should be shielded for 1 to 2 nights, until any hyphema has settled. If bilateral goniotomies are needed, they may be performed in a single anesthesia session, as long as all instruments are sterilized or replaced; all drapes, gowns, and gloves are replaced; and the fellow eye is reprepared and draped in sterile fashion after the first procedure (52).

Mild to moderate hyphemas commonly occur after goniotomy, but they almost always clear rapidly without sequelae over several days. Other complications after goniotomy are rare and include iridodialysis, cyclodialysis, the appearance of small peripheral anterior synechiae in the incised angle, damage to the crystalline lens, and retinal detachment in eyes with high myopia (42, 52).

The results of goniotomy should be evaluated weekly in the immediate postoperative period and are often evident by 3 to 6 weeks. Gonioscopy after successful goniotomy often reveals

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a widened angle in the previous incision site, with improved visibility of the ciliary band and scleral spur (Fig. 40.3). Scattered peripheral anterior synechiae may sometimes develop in the bed of the goniotomy and may even partly obscure a view of the incised angle. Because 4 to 5 clock-hours of angle tissue are incised with a single goniotomy, repeated procedures in untreated portions of the angle may enhance pressure control in selected cases. Goniotomy may fail to control infantile glaucoma in some instances because of improper placement and depth of the angle incision, or the obliteration of the incision by peripheral synechiae. In approximately 10% of cases, if the first two procedures have produced substantial but still inadequate IOP reduction, a third goniotomy procedure may help further lower the IOP (1).

Figure 40.3 Cleft in angle after goniotomy, resulting in a widened angle to the right half of the gonioscopic view in a black infant with primary congenital glaucoma.

The success of goniotomy in controlling glaucoma varies with the cause of the glaucoma. The best results—80% to more than 90% success after one to t wo procedures—are achieved in infants with primary congenital glaucoma presenting between 3 months and 1 year of age (1, 53). Others report lower success of closer to 70% after one to two procedures (54). In one study of seven infants treated with two simultaneous goniotomies in one eye and a single goniotomy in the fellow eye, no significant differences were noted in the results (55). Success rates with goniotomy (and angle surgery in general) are much lower for cases of primary congenital-infantile glaucoma presenting at birth or after 12 months of age (success in these groups is usually about 30% to 50%) (1, 37, 53).

Procedures Related to Goniotomy (Historical Perspective)

Scheie reported a modification of goniotomy, goniopuncture, which involved passage of a goniotomy knife through the trabecular meshwork and sclera to the subconjunctival space after standard goniotomy (56, 57). Scarring of the limbal incision limited the usefulness of goniopuncture.

The Nd:YAG (neodymium:yttrium-aluminum-garnet) laser has been used to perform trabeculopuncture by directing laser energy gonioscopically at the trabecular meshwork, to penetrate through to the Schlemm canal. Success was reported with this procedure in six of eight eyes with juvenile glaucoma over a 6-month follow-up period (58). A technique requiring a large limbal incision, direct goniotomy has also been described, but it has been superseded by trabeculotomy (see later) (59).

Trabeculodialysis, a modification of goniotomy in which the trabecular meshwork is scraped or retracted from the scleral sulcus after a standard goniotomy incision, has been effective in the treatment of children with glaucoma secondary to anterior uveitis (60% pressure control reported in a series of 23 such patients) (39). Goniotomy alone is also effective in these patients (37, 40).

Argon laser trabeculoplasty is ineffective in the treatment of childhood glaucomas and is not feasible to perform in young patients (60, 61).

Trabeculotomy Ab Externo

The surgical technique of trabeculotomy ab externo is performed by cannulating the Schlemm canal from an external approach and then tearing through the trabecular meshwork into the anterior chamber. This procedure thus creates a direct communication between the anterior chamber and Schlemm canal. Burian and Smith independently described trabeculotomy ab externo in 1960 as an alternative procedure to goniotomy (62, 63). The initial technique was later modified by Harms, Dannheim, and McPherson

(1). Success rates varying from 73% to 100% have been reported for this procedure in congenital glaucoma (1). In a series of 140 eyes (89 children) with developmental glaucoma treated with trabeculotomy surgery, overall success was 89% after an average follow-up of 9.5 years (64). While conjunctival scarring and a longer surgical duration are the salient disadvantages of trabeculotomy (compared with goniotomy), this procedure is little affected by an edematous or scarred cornea. (Additional comparison of these two angle procedures follows.)

Basic Technique

In the surgical technique described by McPherson (65), a limbal-based conjunctival flap and a partialthickness triangular or rectangular scleral flap are created as for standard trabeculectomy (see Chapter 38). Most surgeons prefer to perform trabeculotomy under a small fornix-based conjunctival peritomy. Preoperative use of pilocarpine helps to induce miosis, and use of topical apraclonidine may reduce intraoperative bleeding. An inferotemporal approach for trabeculotomy is suggested (unless combined trabeculectomy is planned) to spare the superior quadrants for possible later filtration or other surgery. A radial scratch incision is made in the bed of the scleral flap across the sclerolimbal junction. This scratch incision is gradually deepened under high magnification until the Schlemm canal is identified just anterior to the circumferential fibers of the scleral spur (near the posterior aspect of the limbal “gray zone”). Often a small amount of blood or aqueous

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humor refluxes through the cut ends of the Schlemm canal, and the internal wall of the canal appears slightly pigmented. At this point (or earlier, if preferred, or if the anterior chamber is inadvertently entered before the Schlemm canal is identified), a paracentesis should be made, with injection into the anterior chamber of a small amount of viscoelastic recommended. To confirm the identity of the canal, a 6-0 gauge suture (Prolene with a cautery-blunted tip is recommended) should thread easily to both the left and the right sides of the radial incision. If resistance is met, the suture may need to be repositioned, the radial incision deepened, or a second parallel radial incision made beneath the same scleral flap to assist in finding the Schlemm canal (the presence of the suture in Schlemm canal may sometimes be confirmed by gonioscopy by using a Zeiss four-mirror lens). After the canal has been located, the internal arm of a trabeculotome should be passed gently into the canal (to the right side first for a righthanded surgeon) as far as possible without meeting excessive resistance, and by using the parallel external arm as a guide (Fig. 40.4A). The internal arm is then gently rotated into the anterior chamber, with care to avoid entry into peripheral cornea or beneath the iris plane (Fig. 40.4B). Rotation of the trabeculotome into the anterior chamber tears through the intervening trabecular meshwork and requires little force (Fig. 40.4B, C). Rotation should be halted once about 75% to 80% of the internal arm of the trabeculotome is visible in the anterior chamber. The anterior chamber may shallow slightly, and blood may egress from the torn trabecular meshwork and Schlemm canal as the trabeculotome is removed from the eye along its path of entry. In similar fashion, the trabeculotome should be placed into the left side of the radial incision and the procedure repeated to the left. Leaving a portion of intact trabecular meshwork underlying the radial incision into the Schlemm canal helps prevent prolapse of iris into the wound. The scleral flap is then sutured with 10-0 Vicryl. If a limb us-based conjunctival flap was used, the flap may be closed with a running suture of 8-0 Vicryl as for standard trabeculectomy (66). Alternatively, wing sutures of 10-0 Vicryl often suffice for watertight closure of a fornixbased conjunctival flap. Subconjunctival antibiotic and shortacting steroid may be given at the end of the