CURRENT GLAUCOMA MANAGEMENT 2016

MEDICAL , TRAB, VALVES

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DR DINESH MITTAL DR SONALEE MITTAL

DRISHTI EYE HOSP VIJAYNAGAR INDORE

Central Corneal Thickness and Tonometry • one can take far better care of patients simply by

categorizing corneas as ‘thin,’ ‘average,’ or ‘thick,’ just as it is important to recognize that optic discs come in ‘small,’ ‘medium,’ and ‘large,’ allowing the clinician to interpret disc configurations accordingly. Measuring CCT leads to the discontinuation of therapy in many overtreated ocular hypertensives and escalation of therapy in patients with thin corneas in whom control is clearly inadequate.

Medical Therapy for Glaucoma

Glaucoma Surgery

Preoperative Evaluation and Diagnostic Approach • The importance of a good history-taking, proper clinical

examination and a thorough baseline, pre-operative diagnostic testing are of paramount importance when planning for surgery. It can both guide the physician to a tailor-made surgical approach and also be invaluable after surgery by providing a proper baseline for the post-operative management period. The detailed analysis of the patient’s risk factors for surgical failure are thus of extreme clinical importance for the clinician when planning for surgery. Furthermore, it cannot be overstressed how these risks and possible outcomes should be made clear to the patient when obtaining the appropriate informed consent.

Preoperative Conjunctival Health and Trabeculectomy Outcome • Chronic insult to the conjunctiva can result in ‘priming’ of the

conjunctival cellular profile, potentially resulting in an augmented postoperative fibrotic response following trabeculectomy and higher surgical failure rates. Previous chronic use of topical glaucoma therapy is associated with a proinflammatory conjunctival cellular profile, with significantly more fibroblasts, macrophages, and lymphocytes present in the stroma. Increased expression of inflammatory markers such as HLA-DR is also seen. It would appear that the preservative benzalkonium chloride, present in many topical therapies, is responsible for most of the induced chronic inflammation. Such ‘activation’ of the conjunctiva is associated with significantly reduced success rates for filtration surgery. There is consequently a growing call for more widespread availability of unpreserved formulations of topical glaucoma medication .

Preoperative Conjunctival Health and Trabeculectomy Outcome • Other causes of an activated, profibrotic cellular state

are previous ocular surgery, certain secondary causes of glaucoma, black race, and possibly youth. Thorough preoperative evaluation of risk factors, together with conjunctival examination, will help to determine the level of risk for trabeculectomy failure, allow preoperative treatment to minimize this risk, and determine whether antimetabolites should be employed

Introduction • Trabeculectomy is more likely to be successful when the

blood–aqueous barrier is pristine and conjunctiva untouched, as in the primary glaucomas. However, when anterior segment anatomy is altered, conjunctiva violated, or the blood–aqueous barrier disrupted, trabeculectomy is less effective in the long term, but fortunately offers short-term IOP control in emergency situations. The secondary glaucomas typically fare better with glaucoma drainage devices. Eyes that have severe scarring of the conjunctiva are not good candidates for filtration surgery

Introduction • Subconjunctival fibrosis leading to bleb failure is the most common

cause of trabeculectomy failure. Known risk factors for failure of filtration after trabeculectomy include previous ocular surgery, such as failed initial trabeculectomy, cataract surgery, or any conjunctival incisional procedure; secondary glaucoma due to neovascular, traumatic, or uveitic conditions; race of African origin; long-term therapy with multiple topical antiglaucoma drugs; and young age. Risk factors for failure appear to result in priming the conjunctival cell profile to react more vigorously to surgical insult, leading to enhanced post-trabeculectomy fibrosis. With the growing emphasis on modulation of the wound healing response to achieve greater success rates of filtration surgery, there is increasing recognition of the importance of risk factors for failure

MEDICAL VS SURGICAL• Currently, the majority of glaucoma specialists advocate

trabeculectomy only after medical therapy has failed, this being in spite of the evidence that trabeculectomy is more efficacious in lowering intraocular pressure (IOP) in comparison with medical therapy .

MEDICAL VS SURGICAL• Trabeculectomy and tube shunt both appear to be

attractive surgical alternatives in a select group of glaucoma patients. Patients must understand that although the risk of failure is low in their particular case, the operation may not be successful and that some complication may occur that could make their ocular condition worse. Today, as in decades past, the surgeon and patient together must decide individually which approach is best, but data do exist to help with the decision-making process.

Ophthalmic Anesthesia

Trabeculectomy • Trabeculectomy remains a valuable procedure for pressure

reduction in uncontrolled glaucoma. This procedure consistently lowers IOP into a range that usually prevents further blindness. The physician should better understand basic concepts of filtration surgery and how to best achieve favorable results. The problems with trabeculectomy involve the unpredictable art of wound healing. If excessive scarring occurs, the filter will fail. If inadequate scarring occurs, then the eye will become hypotonous. A fine line exists between excessive scarring and inadequate scarring. This frustration, along with the other inherent flaws with trabeculectomy, will continue to be the driving force behind the desire for improved surgical procedures for our glaucoma patients.

Introduction • Lowering intraocular pressure is currently the only evidence-

based modifiable risk factor for treating glaucoma and no other operation consistently lowers pressure as well as trabeculectomy. In eyes with primary open-angle glaucoma devoid of prior incisional surgery, trabeculectomy remains the gold standard for intraocular pressure (IOP) reduction. Successful trabeculectomy forms an alternative drainage system for the eye that significantly lowers IOP by diverting aqueous humor into the subconjunctival space, establishing a filtering bleb under the upper lid. This diverts aqueous humor away from the patient’s diseased collector system, causing Schlemm’s canal to become smaller

Trabeculectomy• Trabeculectomy is more likely to be successful when the blood–aqueous barrier

is pristine and conjunctiva untouched, as in the primary glaucomas. However, when anterior segment anatomy is altered, conjunctiva violated, or the blood–aqueous barrier disrupted, trabeculectomy is less effective in the long term, but fortunately offers short-term IOP control in emergency situations. The secondary glaucomas typically fare better with glaucoma drainage devices. Eyes that have severe scarring of the conjunctiva are not good candidates for filtration surgery.

• An IOP in the low teens after a filter2 typically stabilizes glaucoma and allays the fear of blindness for all involved in the care of the patient.3 This significantly enhances quality of life for not only the patient and their immediate family, but for all caregivers. The overall socioeconomic burden of glaucoma management is vastly improved after successful filtration surgery because the patient is less dependent on drops, compliance is less of an issue, patient well-being and attitude vastly improve, and clinic follow-up and diagnostic tests are reduced.

Trabeculectomy• The evolution of glaucoma filtering surgery involves

wound modulation with antimetabolites and collagen matrix, placement and timing of antimetabolite application, timing of postoperative suture lysis, improvements in wound architecture, flow regulators, watertight conjunctival closure, and postoperative management.8,9 However, in spite of the surgeon’s best efforts, wound modulation is not always successful; excessive flow may occur, resulting in hypotony or exuberant scarring may occur leading to filtration failure

Trabeculectomy• In addition, an undesirable bleb may develop causing

tearing, burning, leaking, and stinging with foreign body sensation . In spite of these problems, glaucoma surgeons continually turn to trabeculectomy to significantly lower IOP, especially in patients with advanced disc damage or patients intolerant or poorly adherent to medical therapy

Trabeculectomy• Glaucoma surgery is high risk and high maintenance,

requiring intensive postoperative management. Even after successful trabeculectomy surgery, there may be a slight reduction in vision due to a refractive change, astigmatism, reduced axial length, cataract, hypotony, or loss of visual field due to split fixation. Many of these problems are transient and relatively minor when compared to the benefit of vision preservation.

Filtration failure• Severe injection of conjunctiva

post filter with imminent bleb failure. This bleb will fail due to excessive fibrosis associated with high vascularity. A host of fibroblastic factors are brought in by these vessels, leading to scarring of the bleb. Any number of circumstances can produce this scenario, especially a sick blood–aqueous barrier.

Filtration failure• Filter failure with no bleb. This

filter failed 15 years after surgery. It controlled IOP for 10 years and then started failing. Topical medications were restarted and now there is no bleb present. This is the typical scenario of a failing filter. The initial procedure was a limbus-based filter in a 25-year-old African-American male.

Symptomatic filtering bleb

• This bleb has induced considerable astigmatism secondary to extension onto the cornea. This results from a ‘ring of scar tissue’ (blue arrows), that forms secondary to exuberant wound healing at the posterior boundary of this limbus-based trabeculectomy near the conjunctival incision. This scarring prevents any posterior flow of aqueous humor leading to an anterior dissection down onto the cornea. Vision is reduced and a symptomatic bleb is present.

Symptomatic filtering bleb• This bleb is symptomatic

and the IOP is low due to overfiltration. This is an extreme example of a bleb having a ‘mind of its own.’ This symptomatic bleb formed over 10 years and finally required removal and repair with a conjunctival patch graft. This bleb caused chronic irritation, pain, and tearing.

Symptomatic filtering bleb• Repair of eye in Fig. 77-3B

with an autologous conjunctival patch graft. This normalized the IOP and reduced pain, tearing, and foreign body sensation. This eye is now 3 months post repair.

TRABECULECTOMY• The Collaborative Initial Glaucoma Treatment Study

(CIGTS) compared trabeculectomy to medications as initial therapy for primary open-angle glaucoma. The CIGTS supports early surgical intervention for patients who presented with more advanced disease compared to medical therapy. The Tube versus Trabeculectomy (TVT) study has demonstrated that both of these surgical procedures were associated with similar IOP reduction

TRABECULECTOMY• The outcome of filtration surgery is highly dependent on

type of glaucoma, severity of disease, ethnicity, ocular surface disease, pharmacological wound modulation, surgical technique, and skill level. Now we will focuses on the factors most important to a successful filtering procedure.

TRABECULECTOMY• Patients with advanced glaucoma damage, defined as significant

disc damage with rim loss or worrisome visual field loss, require a lower IOP, often in the low teens or possibly single digits in severe cases. These patients are likely better candidates for penetrating surgery such as trabeculectomy. Additionally, socioeconomic factors figure into the decision tree for glaucoma surgery. Patients who are intolerant to glaucoma medications, unable to administer them, poorly adherent to medications, forgetful, or unable to afford medications may fare better with a filter as they will probably be less dependent on topical therapy. Another benefit of filtration surgery is reduction in the magnitude of IOP elevation associated with postural change

Trabeculectomy• Trabeculectomy still remains the most reliable

procedure to lower IOP in the vast majority of patients with uncontrolled POAG devoid of prior incisional ocular surgery. The typical indication for surgical intervention is progressive or anticipated glaucomatous damage that is likely to lead to functional impairment during the patient’s lifetime

THE ANTIMETABOLITE DECISION: NONE, 5-FLUOROURACIL, OR MITOMYCIN C

• excessive fibrosis leading to bleb failure and elevated IOP is consistently the most aggravating problem post filtration. The most common agents to inhibit fibrosis are topical corticosteroids27 and antimetabolites.28 The antimetabolites 5-fluorouracil (5-FU) and mitomycin C (MMC) are used commonly and inhibit fibrosis29 resulting in lower postoperative IOP after trabeculectomy. In a prospective randomized trial comparing trabeculectomy with adjunctive intraoperative 5-FU to placebo, 5-FU increased the success rate with a single intraoperative application.30 In patients at relatively low risk for filtration failure, intraoperative MMC 0.2/mg cc for 2 minutes had similar efficacy as intraoperative 5-FU 50 mg/mL for 5 minutes.31,32 A large retrospective study from the Wilmer Institute found intraoperative MMC more effective than intraoperative 5-FU

Factors Associated with Filtration Failure • 1. Secondary glaucomas • Neovascular glaucoma • Aphakia • Uveitis • Traumatic • 2. African race • 3. Prior failed filtration • 4. Young age

Factors Associated with Filtration Failure • 5. Diabetes • 6. Superior rectus bridle suture • 7. The need for a very low postoperative IOP• 8. Combined cataract and glaucoma surgery (use MMC) • 9. Conjunctival scarring (example from scleral buckle

surgery) • 10. Pseudophakia

Factors Associated with Filtration Failure • 11. Any situation that changes the blood–aqueous barrier • 12. Altered anterior segment anatomy (example

penetrating keratoplasty) • 13. Ocular surface disease such as ocular rosacea • 14. Surgeon experience• 15. Postoperative inflammation• 16. Subconjunctival anesthetic • 17. High IOP during the first 2 weeks post-filtration surgery

BLEB CHARACTERISTICS AND MORPHOLOGY • The heart of glaucoma surgery is the maturation of the bleb,

especially during the first 3 postoperative months The most desirable blebs are shallow, widespread, pale but not avascular, limited to under the upper lid, and rapidly develop epithelial microcysts . A plethora of microcysts seen during slit-lamp exam almost always correlates well with a favorable outcome. These microcysts are located at the level of the epithelium and contain proteinacous debris. Microcysts represent clinical and laboratory evidence for transconjunctival movement of aqueous post filtration surgery. Many blebs start out this way, but over a 3-month period become localized . These blebs become cystic, localized, elevated, and ultimately pale and avascular

BLEB CHARACTERISTICS AND MORPHOLOGY • The wall of the bleb may thicken or become very thin

(both of which are undesirable). Opinions vary greatly as to how to best achieve the ultimate bleb. Filtering blebs47 show decreases in overall epithelial thickness, goblet cell density, and vascularity. There is also a loss of localized stromal vascularity. These characteristics clearly explain the increased risk of blebitis and endophthalmitis.

Bleb Grading Scale• Mitomycin C has a dramatic effect on bleb evolution. The mean time to

bleb avascularity post MMC-augmented trabeculectomy is approximately 100 days when the MMC is applied directly over the filtering site. This avascularity is the key factor leading to bleb leaks seen in 26% of eyes at 2 years. Many physicians use a bleb grading scale to try to better understand bleb characteristics and follow bleb morphology. In the Indiana Bleb Grading Scale,50 the height, extent, vascularity, and Seidel leakage of the bleb are routinely graded. This scale is helpful in understanding the clinical appearance of the bleb and understanding postoperative bleb evolution and function. For example, the bleb in Figure 77-1B has the characteristics H2E2V2S0. This implies moderate bleb height (H), 2 to 4 clock hours of elevation (E), mild vascularity (V), and no Seidel (S). The bleb in Figure 77-2A is H1E2V4S0, implying a shallow bleb, with an extent of 2 to 4 clock hours but highly vascular with no leak

The optimal bleb post fornix-based trabeculectomy• Bleb appearance. This slit-lamp

photograph illustrates the characteristics of the perfect bleb. The bleb is totally asymptomatic, delivering an excellent IOP of 12 mmHg without topical medications, 5 years later. The desirable features include a diffuse, shallow bleb. The bleb is largely pale but yet slightly vascular, definitely not avascular. There are many microcysts present. The bleb is not too thin in any area. The patient has no bleb-related symptoms: no tearing, no burning, and no foreign body sensation. The bleb does not induce astigmatism or any type of dysesthesia.

The optimal bleb post limbus-based trabeculectomy

• Bleb appearance. The blue arrows point to the conjunctival incision. Often, this area will scar and the incision is pulled towards the limbus. This did not occur in this case. This bleb has the desirable characteristics of good IOP control, shallow and diffuse, some vessels on the surface, with an overall pale appearance but not avascular. This bleb is slightly more elevated over the filtration site, which is more common with a limbus-based filter.

Operative Technique

LIMBAL ANATOMY• The limbal blue zone, or surgical limbus, is roughly 1.5 mm and is

the most important anatomic landmark for glaucoma surgery. The anterior extent of the blue zone is the corneolimbal junction and the posterior extent is the junction with the sclera, the sclerolimbal junction. A perpendicular incision made at the posterior extent of the blue zone, the sclerolimbal junction, would enter the anterior chamber at the anterior meshwork/Schwalbe’s line area as shown in Figure 77-5 B and C. Therefore, the scleral spur is located posterior to the blue surgical zone. Figure 77-5 demonstrates how far posterior the scleral spur may be, for this anatomy varies widely and must be determined by the surgeon intraoperatively. Knowledge of these angle structures is key when performing a trabeculectomy as well as when performing an Ex-Press shunt

Limbal anatomy• (A) Limbal anatomy is highly

variable. The limbal zone is a 1.5 mm transition area between sclera and cornea. The posterior extent of this blue zone is noted by the blue arrow and the anterior extent by the green arrow. Obviously, the scleral spur can not be seen but, in general, a perpendicular incision through sclera at the blue arrow would be near the anterior trabecular meshwork/Schwalbe’s line. The black arrow is the actual position of the spur as seen after the dissection in the figure. (

Limbal anatomy• The black arrow denotes the scleral

spur, and Schlemm’s canal is located directly anterior to the spur. Schwalbe’s line is seen as the peripheral extent of the cornea (blue arrow). The most common error during filtration surgery is flap location with failure to extend the flap far enough posteriorly or anteriorly. This flap appears to have adequate posterior extension, but note the posterior extent of scleral spur. The problem with a short flap would be failure to adequately cover the sclerostomy.

Limbal anatomy• Correlate the anatomy

beneath the scleral flap in Fig. 77-5B with the gonioscopic view. The scleral spur is the black arrow and Schwalbe’s line the blue arrow

FORNIX-BASED CONJUNCTIVAL INCISION• Many investigators believe a fornix-based conjunctival

flap is better than a limbus-based one. Kano and Kuwayama evaluated the characteristics of filtering blebs after a fornix-based approach and found most blebs were pale, diffuse, and leak-free. The majority had diffuse blebs at 72%, with 60% vascular. There were no late-onset bleb leaks and cystic blebs were uncommon

LIMBUS-BASED CONJUNCTIVAL FLAPS • In pediatric and young adult filters with high-dose

antimetabolites, the risk of a cystic bleb developing is much greater with a limbus-based conjunctival flap (90%) than a fornix-based flap (29%). In addition, late hypotony and blebitis were more common with a limbus-based approach. Wells et al. felt strongly that a limbus-based approach was much more likely to lead to a cystic bleb in young patients.54 The authors have certainly seen a similar outcome in adults

LIMBUS-BASED CONJUNCTIVAL FLAPS • hypotony was more common with fornix-based filters.

The same study found limbus-based filters to be higher and more avascular and slightly more prone to blebitis. Morita and colleagues used in vivo confocal microscopy and ultrasound to study blebs. They found limbus-based filters had a higher height of the fluid-filled space, along with a thinner wall of the bleb, lower density of subepithelial connective tissue and a greater avascularity of subepithelial tissue than fornix-based filters. These characteristics of a limbus-based filter may be associated with long-term leaks and related problems.

FORNIX-BASED TRABECULECTOMY • Fornix-based filters are experiencing a renaissance.

Many investigators feel that bleb characteristics are more desirable with a fornix-based approach, with less symptomatic blebs that are free from long-term leaks In addition, a fornix-based conjunctival flap is preferable for eyes that have conjunctival scarring. Patients with enophthalmos or small palpebral fissures are clearly candidates for a fornix-based approach

FORNIX- VERSUS LIMBUS-BASED CONJUNCTIVAL FLAPS• (A) The conjunctival

incision for a limbus-based approach is made approximately 10 mm from the limbus. At this location, it is common to detect some underlying Tenon’s capsule that facilitates the final closure

FORNIX- VERSUS LIMBUS-BASED CONJUNCTIVAL FLAPS• (B) This eye is 4 months

post filter, limbus-based approach, and note the incision is well back from the limbus, the eye is quiet, and a diffuse bleb formed

FORNIX- VERSUS LIMBUS-BASED CONJUNCTIVAL FLAPS• (C) In this case, the incision

noted by the blue arrows is migrating towards the limbus, the vessels are engorged and injected, and this bleb will probably turn cystic, pale and avascular. This wall of scar tissue will be a barrier to posterior flow of aqueous, creating a more forward, undesirable cystic bleb

FORNIX- VERSUS LIMBUS-BASED CONJUNCTIVAL FLAPS• (D) When the incision

migrates forward or is associated with excessive scarring, the bleb turns pale and avascular and the suture line is seen at the posterior aspect of the bleb. Because the bleb area is limited, the IOP control is often marginal.

FORNIX- VERSUS LIMBUS-BASED CONJUNCTIVAL FLAPS• (E) The conjunctival

incision for a fornix-based approach is at the limbus, for the nomenclature for fornix- or limbus-based is where the flap hinges, not where it is incised

FORNIX- VERSUS LIMBUS-BASED CONJUNCTIVAL FLAPS• (F) In the majority of cases, the

bleb develops as seen in . However, in this case, a cystic bleb with thin conjunctiva developed in spite of the approach, and the antimetabolite was placed posterior to the filtration site. Even under the best of circumstances, either with a fornix- or limbus-based approach, an undesirable bleb may form

A diffuse shallow desirable bleb created with a fornix-based approach.

Anatomy of a bleb• Anatomy of a bleb as seen

with high-resolution ultrasound from iScience corporation, Menlo Park, CA. The wall of the bleb appears thick, but it functions quite well, with an IOP of 12 mmHg.

Anatomy of a bleb• A pale, avascular cystic

bleb following a limbus-based trabeculectomy in the fellow eye of the patient featured in Figures 77-6G and 77-6H. The wall is thin and worrisome from an infectious viewpoint. In addition, the bleb was symptomatic

Anatomy of a bleb• A high-resolution

ultrasound image of a pale avascular bleb, allowing one to better appreciate bleb anatomy and function.

Mitomycin C • Mitomycin C applied intraoperatively was the first

antifibrotic agent used to increase the success of fil tration surgery Concentrations of 0.2 to 0.5 mg/ ml for 2 to 5 minutes have been used.. MMC is more potent than 5-FU7 . Higher concentrations and longer duration are associated withgreatereffectbutwith a greater likelihood of complications, like a very thin avascular bleb and post-operative hypotony.8,9 Most surgeons currently use a concentration of 0.2 or 0.4 mg/ml for 2 to 3 minutes.

Method of Application of MMC• MMC-soaked sponge (Mersel or polyvinyl) is placed on the intact

scleral surface before dissecting the scleral flap. This technique may reduce the penetration of the drug to the ciliary body, where it can cause prolonged postoperative hypotony and prevents drug entry into the anterior chamber where it may cause endothelial toxicity. The conjunctiva and tenon’s capsule is draped over the sponge, making sure that the cut edge does not come in contact with it. The surgical site is irrigated with 15 to 30 ml of balanced salt solution, which is collected on gauze pads. The remainder of the trabeculectomy is performed as described previously, with special attention given to creating a tight closure of the scleral flap, in order to maintain a formed anterior chamber, and performing a watertight conjunctival closure using a tapered needle.

Mitomycin MMC soaked sponges are used for intraoperative application

FORNIX-BASED TRABECULECTOMY

FORNIX-BASED TRABECULECTOMY • Fornix-based filters are experiencing a renaissance.

Many investigators feel that bleb characteristics are more desirable with a fornix-based approach, with less symptomatic blebs that are free from long-term leaks. In addition, a fornix-based conjunctival flap is preferable for eyes that have conjunctival scarring. Patients with enophthalmos or small palpebral fissures are clearly candidates for a fornix-based approach

TRACTION SUTURE, MANAGEMENT OF TENON’S CAPSULE, AND CREATION OF A FORNIX-BASED INCISION

• A corneal traction suture is preferable to a superior rectus bridle suture for several reasons. The bridle suture creates undesirable holes in the conjunctiva and has a potential to perforate the globe during passage of the needle. The globe is rotated inferiorly (as seen in Fig. 77-7A) by pinching the drape around the suture with a hemostat

Corneal traction suture.• (A) An 8-0 polyglactin

superior corneal traction suture is placed two-thirds thickness into peripheral clear cornea and the globe is rotated down to expose the superior conjunctiva. Failure to adequately expose the area of regard makes surgery much more difficult.

TRACTION SUTURE, MANAGEMENT OF TENON’S CAPSULE, AND CREATION OF A FORNIX-BASED INCISION

• Tent the limbal conjunctiva up about 1 mm from the limbus and incise the conjunctiva, creating a peritomy. The conjunctiva and Tenon’s capsule is incised at the limbus for 5–7 mm using Westcott scissors (Fig. 77-7B). Occasionally, a radial conjunctival relaxing incision is required to gain adequate exposure. It is imperative to hug the limbus while pressing the scissors against the conjunctiva to sever it at its insertion to the limbus. The authors prefer to visualize the insertion of Tenon’s capsule while elevating the conjunctiva, so that both tissues can be incised at the same time

conjunctival incision• (B) Fornix-based

conjunctival incision. Incise the conjunctiva with sharp Westcott scissors. It may be necessary to create a small radial cut to start the dissection.

TRACTION SUTURE, MANAGEMENT OF TENON’S CAPSULE, AND CREATION OF A FORNIX-BASED INCISION

• Use blunt-tipped Westcott scissors to fashion a subconjunctival pocket by dissecting the conjunctiva and Tenon’s capsule off the episclera (Fig. 77-7C). Avoid the superior rectus during the dissection. The conjunctiva must only be manipulated with atraumatic forceps. If buttonholes occur during dissection, the defect can be repaired by incorporating Tenon’s tissue during the conjunctival closure. During complicated conjunctival closure, the authors prefer to use a tapered 10-0 microvascular needle

FORNIX-BASED INCISION• (C) Attachment of Tenon’s capsule near the

limbus. The conjunctiva and Tenon’s capsule fuse as the tissues approach the limbus. Approximately 1.5 mm from the limbus, Tenon’s capsule fuses with the underlying episclera as seen at the black arrow. Sever these adhesions with the blunt Westcott scissors resting on the sclera to avoid tearing the tissue. Avoid a buttonhole of the conjunctiva at this area (black arrow). Once Tenon’s is separated from the sclera, dissect it as a single layer with the conjunctiva. Tenon’s is also attached to the sclera in the area adjacent to the insertion of the superior rectus muscle. The insertion of the conjunctiva onto the cornea is variable; occasionally, the insertion is more anterior than anticipated

CREATION OF A FORNIX-BASED INCISION • It is essential to incorporate Tenon’s capsule when

closing the conjunctiva (Fig. 77-7D). In this era of antimetabolites, just enough Tenon’s capsule is removed to visualize the underlying scleral flap sutures. Leaving a thin layer of Tenon’s capsule reduces long-term bleb breakdown, hypotony, and endophthalmitis, but an excess of Tenon’s capsule may lead to fibrosis and filtration failure

FORNIX-BASED INCISION • (D) Edge of Tenon’s and

conjunctiva. The anterior edge of Tenon’s is located by the blue arrow. If excessive, which is uncommon, it may be slightly trimmed. The key is to free the Tenon’s fascia from the episclera and then grasp the edges of both conjunctiva and Tenon’s when separating the two layers from the rest of the underlying sclera. Protecting the edge of Tenon’s is important, for it serves as a gasket to prevent leaks at the limbus during the postoperative period.

FORNIX-BASED INCISION • (E) Blunt dissection of

conjunctiva. Dissect Tenon’s and conjunctiva from the episclera with blunt Westcott scissors. It is important to continually visualize the tips of the scissors during the dissection to prevent perforation. In addition, the dissection is aimed towards the quadrants on either side of the insertion of the superior rectus muscle. (

APPLICATION OF ANTIMETABOLITE • The decisions regarding antimetabolite use must be

made prior to surgery. Typically, the greater the number and magnitude of risk factors for filtration failure, the more potent the antimetabolite. The first decision is whether the case carries a low, medium, or high risk for failure. For low risk of failure, some surgeons prefer no antimetabolite. Postoperatively, if the bleb is injected, a series of 5 mg 5-fluorouracil (5-FU) injections is administered into the inferior cul-de-sac or adjacent to the bleb.

Application of MMC soaked sponges• (F) The general theme of

MMC application is to cover a broad area with several sponges, all placed posterior to the intended area of filtration. The concentration and time of application vary, depending on risk factors.

Application of MMC soaked sponges• (G) Notice how far

posterior the sponge is located; it is placed, well away from the intended area of filtration. Do not place the sponge directly over the scleral flap, for this may lead to scleromalacia of the flap.

Application of MMC soaked sponges• (H) The authors typically use

three MMC pledgets, soaked in MMC, 0.2 mg/mL, placed for 2–5 minutes, depending on the case. After the specified time, the pledgets are removed, sponge count performed, and the area is vigorously irrigated with balanced salt solution (BSS). With posterior sponge placement, the sponge is out of sight and easily forgotten. A well-trained and vigilant surgical assistant keeps track of the sponge count.

APPLICATION OF ANTIMETABOLITE • For medium-risk cases, either an intraoperative sponge

application of 0.1 mL of 5-FU (50 mg/mL) for 5 minutes or low-dose mitomycin C (MMC) (0.2 mg/mL for 2–5 minutes) is indicated, and postoperative injections of 5-FU titrated if necessary. If only one risk factor is present, 2–3 minutes of MMC application is appropriate; for multiple risk factors, 3–5 minutes.

APPLICATION OF ANTIMETABOLITE • For high-risk eyes, some surgeons use MMC (0.4 mg/mL)

for a period of 2–5 minutes. However, if these potent concentrations are used in low- or medium-risk eyes, long-term hypotony and bleb breakdown are more likely. Prior to scleral flap dissection, a rectangular segment of Merocel instrument wipe or Weck-cell sponge soaked with either 5-FU 50 mg/mL or MMC is placed posterior to the intended site of filtration.

APPLICATION OF ANTIMETABOLITE • Avoid placing it directly over the area of intended

filtration for this leads to pale avascular blebs. Immediately after the pledget has been placed, any pools of antimetabolite present are soaked up using a Weck-cell sponge, which is discarded. The size of the pledget varies and is not standardized; the surgeon uses best judgment depending on risk factors and anatomy

APPLICATION OF ANTIMETABOLITE • The conjunctiva is retracted, the sponge is removed,

and copious irrigation applied to the contacted area. The use of MMC is nearly ubiquitous in glaucoma surgery, however glaucoma specialists are constantly looking for improved alternatives which may allow for a better and safer bleb.

APPLICATION OF ANTIMETABOLITE • One potential wound-modulating material currently being investigated

is Ologen (Aeon Astron Europe B.V.), a porous collagen matrix that is thought to modulate wound healing. Theoretically, the major functions of this collagen matrix are achieved by physical principles rather than chemical ones. The proposed mechanism of bleb formation is not by suppressing or inhibiting fibroblast growth, but rather guiding fibroblasts to grow randomly inside the matrix. Modulating fibroblast behavior is thought to produce a more physiological environment without scar formation, thus creating a sub-conjunctival space for a bleb and theoretically preventing hypotony.58–62 The collagen matrix is thought to eventually biodegrade within 90–180 days. Although fundamental studies of Ologen demonstrating efficacy are currently underway, there are currently no studies demonstrating the long-term success of Ologen.

OUTLINE SCLERAL FLAP • The flap is first outlined prior to its dissection. A variety of

instruments may be used to dissect the partial-thickness scleral flap, such as a No. 67 Beaver blade, razor blade, or Greishauber blade. The choice of instrument is by surgeon’s preference and may vary slightly from case to case. Initially, the borders of the flap are outlined to two-thirds of the scleral thickness. If the flap is too thin, it has a tendency to shred. Extreme care should be taken with myopic eyes as the sclera is typically thinner than average. Special precautions are necessary when flaps are fashioned in eyes that have undergone previous limbal surgery, especially prior filtration or cataract surgery.

Incise and outline sclera• (I) Incise the sclera with a

super sharp blade approximately 5 mm from the limbus for a chord length of 3 mm. The depth should be two-thirds thickness. Note the length of the conjunctiva incision at the limbus, which can vary from 5 mm to 7 mm depending on the size of the eye and exposure.

Incise and outline sclera

• (J) The most common error relates to the depth of the incision. The tendency is to go one-quarter or one-half depth for fear of penetrating the choroid. If the initial incision is not deep enough, the flap, as it is dissected, is more likely to shred during manipulation or buttonhole during flap closure.

Incise and outline sclera• (K) Proper depth is determined

by retracting the sides of the incision and inspecting the depth. A good sign is a light-gray color as seen in the depths of the incision as the floor of the sclera is reached. If too deep, the choroid will appear, clearly a red flag to cease dissection. When there is excessive bleeding in the surgical field and inadequate hemostasis, one can easily misjudge flap thickness and run into problems.

Incise and outline sclera• (L) The shape of the scleral flap is the

surgeon’s preference. A trapezoidal flap is useful with a fornix-based conjunctival incision because the posterior edge of the flap is closer to the limbus where there is room to work. The apex of a triangular-shaped flap would be located under the conjunctiva, making it difficult to suture. The lateral sides of the flap should extend into clear cornea at the limbal transition zone. The depth of the incision is inspected (black arrow) to make sure of adequate exposure.

Incise and outline sclera• (M) The flap is outlined. The

sides and base are 5 mm and the top is 3 mm. When first learning how to fashion a scleral flap, it is preferable to err on a larger size such as in this example, for a larger-sized flap is more forgiving during a recovery maneuver such as for inadequate depth. In addition, if the posterior margin of the flap is too anterior, there is not adequate coverage of the sclerectomy site.

FASHION SCLERAL FLAP

Fashion scleral flap• (N) There are several

instruments available for flap dissection. A supersharp blade works well to initiate the appropriate depth of the incision at two-thirds thickness. It may take a millimeter to find the correct plane: again, another reason to learn with generous flaps as they are more forgiving.

Fashion scleral flap• (O) Once the correct plane is

achieved, use a curved Grieshaber blade to advance the flap in the same plane towards the limbus. As the scleral spur, or corneoscleral sulcus, is approached, the curvature of the globe changes and a more anterior plane must be followed. If a more anterior plane is not obtained, the dissection will go through the spur and trabecula and into the anterior chamber or, even worse, into the choroid.

Fashion scleral flap• (P) The black arrow denotes the

scleral spur and the green arrow Schwalbe’s line. Carry the dissection well into clear cornea to ensure adequate removal of trabecular and associated tissue anterior to the scleral spur. Any removal of sclera posterior to the black arrow will potentially create a cyclodialysis cleft, as in the old Watson-type trabeculectomy. In addition, removal of tissue posterior to the spur results in considerable bleeding.

scleral flap• (P1) A crescent blade

dissection is another method to create a scleral flap. Physicians familiar with creating a scleral tunnel for cataract surgery are familiar with this technique. After making the tunnel, simply use Vannas scissors to create the sides of the flap.

scleral flap• (P2) A minispoon blade is

another useful instrument for creating a flap. Once the flap is initiated, this curved minispoon blade allows a very fine dissection of the flap. Use very purposeful movements, hugging the scleral bed and dissecting while there is tension on the flap as it is retracted. Careful tension on the distal end of the flap in anterior direction will aid in an even and consistent dissection.

FLAP SIZE. • In general, the shape of the flap does not matter as long as it

is constructed properly and is able to cover the corneoscleral block removal site adequately. Flap size will vary according to the adjacent anatomy. Most trapezoidal flaps range between 4–5 mm at their base and sides with the posterior limit at 2–3 mm. Triangular flaps may be slightly smaller. Thin flaps tear or avulse from the bed and may tear during suture closure. Dissection into clear cornea assures adequate room for removal of the corneoscleral block. Thick flaps probably are not detrimental because postoperatively the bulk of flow occurs through the wound margins of the scleral flap

FLAP LOCATION • The dissection is kept as close to the 12 o’clock position

as possible because excessive medial or lateral flap placement leads to symptomatic filtering blebs and potentially would interfere with future tube placement. Prior to glaucoma drainage implants, some physicians preferred to place the filter on either side of the 12 o’clock position. If the first filter failed, a second could be made in the adjacent quadrant. This, however, would make it more difficult to insert a drainage implant, the placement and usage of which is increasing over a second filter.

FLAP DISSECTION • Flap dissection must be initiated at one of the posterior

corners of the flap. Once an edge has been dissected, the freehand dissection is carried forward uniformly into clear cornea anterior to the trabecular meshwork. This assures enough room for block removal without removal of scleral spur, which may lead to an inadvertent cyclodialysis and considerable bleeding.

FLAP DISSECTION • In eyes with previous limbal cataract surgery, a scleral

tunnel technique is beneficial. A scleral tunnel incision minimizes the traction on the flap and is less likely to cause the flap to break at the old incision line. The scleral tunnel is constructed by creating a two-thirds-thickness incision of sclera tangentially, 3–4 mm posterior to the limbus, for a width of 3–4 mm. Use a crescent blade to tunnel into clear cornea in the same fashion as for cataract surgery. Slide the blade from side to side until the flap is about 4 mm in width. The flap is finished by using Vannas scissors to incise the lateral edges, thus creating a three-sided flap

PREPLACED SCLERAL FLAP SUTURES • Flap sutures are much easier to place before the eye is

hypotonous. The flap sutures should not be full thickness, as this may cause a leak.

Preplaced scleral flap sutures.• Q) The less time the eye is open

to atmospheric pressure, the less the likelihood of a suprachoroidal hemorrhage or related event. Therefore, preplaced flap sutures are extremely useful for rapidly closing the wound. Observe that the suture exits the side of the flap, not through the bottom of the flap. This prevents a buttonhole from forming in a thin flap. A 10-0 nylon suture is effective for flap closure.

PARACENTESIS • The eye must be relatively

firm to create a paracentesis tract. The uses are multiple

Paracentesis.• (R) Paracentesis is one of

the most important steps during filtration surgery (see Box 77-5). Use a supersharp blade to enter completely through the cornea and into the anterior chamber. Incomplete penetration may lead to a Descemet’s detachment. (S–V) Removal of corneal–trabecular–scleral block.

REMOVAL OF CORNEOSCLERAL BLOCK • Rotate the scleral flap over the cornea and use a 15° supersharp blade

to enter the anterior chamber at the anterior extent of the scleral bed. Insert the punch through the slit into the anterior chamber and engage the lip of the scleral bed. Remove a few sections of tissue to create an adequate block removal. Light wet-field cautery is applied to the cut ends of Schlemm’s canal, which significantly reduces the chance of a postoperative hyphema. The size of the corneoscleral block in relation to the dimensions of the scleral bed determines the amount of flow through the filter. A very large corneoscleral block leaves a small scleral ledge, which may result in overfiltration and hypotony.63 If the corneoscleral block is too small, the ledge is too large and it is difficult to achieve flow through the flap, especially if it is secured tightly. Excessive posterior block removal into the ciliary body may cause an inadvertent cyclodialysis cleft and bleeding.

REMOVAL OF CORNEOSCLERAL BLOCK • (S) Use a supersharp

blade to enter the anterior chamber at the anterior extent of the scleral–corneal bed. Take care to avoid the iris and visualize the tip of the blade as it enters the anterior chamber. Incise a 2–3 mm area for insertion of the punch. (

PUNCH• (T) A side view of the

punch is shown. The punch removes approximately a 1 mm portion of limbal tissue.

PUNCH• (U) The obvious reason to

start anteriorly with the punch is to avoid cutting into the ciliary body structures located posterior to the spur. These structures bleed profusely.

PUNCH• (V) The punch facilitates a

simple removal of tissue. The majority of this block removal is corneal tissue. • Figure 77-7 Continued

PERIPHERAL IRIDECTOMY • Even though iridectomy is rarely needed in modern-day

cataract surgery, it is required for filtration procedures to relieve pupillary block and prevent obstruction of the internal filter opening. After removal of the corneoscleral block, the iris typically obstructs the opening. If the iris bulges through the block site and is difficult to reposit, use the DeWecker scissors to make a small iridotomy in the peripheral iris to relieve the pupil block. This maneuver usually allows the iris to recede back into the anterior chamber. The base of the iris is then grasped using 0.12 forceps and retracted outside the posterior ledge of the opening in a tangential fashion.

Peripheral iridectomy• W) Occasionally, the iris

will prolapse into the sclerostomy site immediately after removing the corneoscleral block. Do not try to push it back into the eye, as this will damage the iris.

Peripheral iridectomy• (X) Instead, make an

iridotomy prior to the iridectomy. The iridotomy will relieve the pressure in the posterior chamber that is pushing the iris out of the eye. It is less damaging to the iris to gently reposition it after the iridotomy with relief of posterior pressure.

Peripheral iridectomy• (Y) The iris is grasped with

a 0.12 forceps and elevated above the plane of the sclerectomy site. A DeWecker scissors is convenient to remove a section of iris, thereby creating the iridectomy.

Peripheral iridectomy• (Z) After removing the

peripheral iris, check the site for vitreous with a Weck-cell sponge. If there is any remnant of the posterior layer of the iris, remove with a Weck-cell sponge. (

PERIPHERAL IRIDECTOMY • A small peripheral section of iris is removed using

DeWecker scissors. Aqueous humor pours forth from the posterior chamber when either the iridotomy or iridectomy is accomplished. If no fluid is seen, aqueous misdirection syndrome must be suspected (see Chapter 84). The iridectomy size should approximate the size of the block. The patency is checked by direct observation of lens capsule or red reflex. Posterior pigment epithelium is removed using a sponge if needed. In a pseudophakic eye that has a large posterior capsulotomy, or in aphakic eyes, vitreous may appear.

PERIPHERAL IRIDECTOMY • In rare instances, a peripheral iridectomy may be

unnecessary, especially if it might cause vitreous prolapse. To prevent obstruction of the sclerostomy, a large basal iridectomy (much larger than the size of the stoma), is routine for secondary glaucomas such as neovascular, iridocorneal endothelialization syndrome, posterior polymorphous dystrophy, as well as all other diseases that tend to cause broad peripheral anterior synechiae (PAS).

SCLERAL FLAP CLOSURE • After the iridectomy, the eye is quite soft. Immediately,

instead of completely tying each suture in a 3-1-1 configuration, secure each one with the first three loops of the knot. Insufflate the anterior chamber to raise the IOP, roughly gauge the flow through the flap, and finish tying the two posterior sutures. Finish tying the two anterior sutures at the limbus. This typically leaves two mid sutures to close with just the correct amount of tension to have flow through the flap. If the flap is closed too tightly, no flow occurs and postoperative IOP is elevated. If the flap is closed too loosely, overfiltration occurs. Gauging the proper flow through the filter site is a difficult art, but a critical step in successful filtration surgery.

SCLERAL FLAP CLOSURE • A scant ooze of aqueous through the scleral flap is a

reasonable end point, which is attained by the adjustment and replacement of sutures as necessary. This additional operative time may save hours of postoperative work. • It is always safer to err on the side of extra flap sutures.

High IOP is easier to treat using scleral flap suture lysis than a return to surgery to place additional sutures. If the sutures cannot be seen intraoperatively, Tenon’s capsule is excised until they are visible.

Closure of scleral flap with adequate aqueous egress.

• (AA) All of the preplaced sutures are temporarily tied, starting with the posterior set. The anterior chamber is insufflated with BSS to normalize IOP. The flow through the flap is adjusted by tightening the sutures trying to direct flow away from the limbus. Initially, there were six sutures in the flap, but one additional suture on the temporal side was added due to excessive flow. This additional temporal suture will be the first one to laser postoperatively if additional flow is needed.

SCLERAL FLAP CLOSURE • As an alternative to laser suture lysis, some surgeons

prefer the placement of releasable sutures when the scleral flap is closed. These have a slip knot, the loose end of which is superficially buried in the cornea, and can be removed using forceps at the slit lamp at any stage postoperatively; no thinning of the Tenon’s capsule is required (see Spotlight 1 on Releasable Sutures by Mark Sherwood at the end of this chapter).

FORNIX-BASED CONJUNCTIVAL CLOSURE • There are a variety of techniques to close the conjunctiva.

Hooded techniques are the simplest, but the most prone to leaks, especially with antimetabolite use. A horizontal mattress suture technique described by Wise64 is the most time consuming and precise, and yields the best results. A tapered 2850 9-0 nylon needle that has a tiny cutting tip is used. It is essential to keep the limbal suture bite longer than the distance between the corresponding conjunctival suture holes. When the suture is tightened, the intervening conjunctiva stretches tightly against the sclera. This is very effective in the prevention of wound leaks.

FORNIX-BASED CONJUNCTIVAL CLOSURE • (AB) Conjunctival closure.

Closure of the conjunctiva is a meticulous process in order to achieve a watertight closure. This is imperative for the success of the filter.

FORNIX-BASED CONJUNCTIVAL CLOSURE • a more straightforward and less time-consuming technique which

involves a 10.0 nylon suture and running and mattress style sutures, the second clip a running mattress as initially described by Jim Wise MD (See Videos 77-1 and 77-2). This approach is effective yet time consuming and may be best for patients with extremely friable conjunctiva and thin Tenon’s capsule. As with all techniques, the most dependent variable is individual surgeon comfort and experience. One should try as many techniques as possible and attain proficiency in 2–3 approaches to maximize efficiency and flexibility. In cases where the conjunctiva is severely thin, one must entertain the idea of attempting a different glaucoma procedure and avoiding a trabeculectomy all together.

INSUFFLATE THE BLEB • Insufflate the bleb to check for leaks, a critical step in

the evaluation of proper wound closure.

Test the wound.• (AC) Test the wound.

Inject BSS in the anterior chamber through the paracentesis and insufflate the bleb to check for leaks. Place additional sutures as needed to guarantee a watertight closure.

LIMBUS-BASED TRABECULECTOMY Filtration surgery requires the physician to master two types of conjunctival entry incision: fornix-based and limbus-based.

GENERAL PRINCIPLES CONCERNING REVISION OF A FILTER • If a filter fails after several years but the surgeon feels

that revising it would be useful, then the skills necessary for this should be emphasized. The most common scenario is a functional trabeculectomy that fails post cataract surgery. The IOP becomes more difficult to control, medical therapy is revisited, and ultimately revision is required with uncontrolled IOP.

Failed fornix-based trabeculectomy requiring trabeculectomy revision.• (A) This filter worked well for

several years until routine uncomplicated clear corneal cataract surgery. The prior trabeculectomy was fornix-based. Either a repeat fornix-based approach may be used or, as in this case, a limbus-based conjunctival approach. The superior conjunctiva is easy to incise with this approach, for the tissue in this area was not violated during the initial filter.

GENERAL PRINCIPLES CONCERNING REVISION OF A FILTER • If the prior wound is fornix-based, then the conjunctiva

towards the fornix is virgin territory and may be an easier approach for the wound revision if the exposure is good. Patients with severe enophthalmos may require a fornix-based approach. If the surgeon is not comfortable with the revision, then consider an aqueous drainage implant. These devices are becoming more common in eyes with previous filtration failure, and many doctors are using these shunts as first-line therapy in pseudophakic eyes, especially following the 5-year results of the TVT trial

GENERAL PRINCIPLES CONCERNING REVISION OF A FILTER • demonstrates the necessary steps for a limbus-based

approach to revising a bleb in an eye that has previously undergone a fornix-based filtration surgery. Obviously, this approach is applicable for primary trabeculectomy and any limbus-based approach. Figure 77-9A also highlights several useful maneuvers in an eye that has had conjunctival surgery of any type. • In general, limbus-based surgery requires an experienced

assistant because of the need for conjunctival flap retraction. If the surgeon does not have adequate help for the procedure, a fornix-based approach is recommended

CORNEAL TRACTION SUTURE • A corneal traction suture is required for adequate

conjunctival exposure of the failed bleb in Figure 77-9A. This is the same maneuver as in the fornix-based approach. Failure to obtain adequate exposure remains the most common error in limbus-based trabeculectomy.

Corneal traction suture.• (B) Adequate exposure of the

operative site is the key ingredient during a limbus-based conjunctival approach. This is accomplished by placing an 8-0 Vicryl suture two-thirds thickness through the cornea at the 11 to 1 o’clock positions. Avoid perforating the eye, which may induce a low IOP. The low IOP makes it more difficult to construct a flap. If this occurs, the puncture site may be hydrated with balanced salt solution to close the leak and increase IOP. (

ROTATE AND INSUFFLATE • Rotate the globe inferiorly (Fig. 77-9C) and secure the traction suture to

the drape. There are a variety of traction sutures; the technique demonstrated in this figure is a simple one. Once the globe is properly positioned, pierce the conjunctiva 10 mm from the limbus with the 30-gauge needle and insufflate the conjunctiva with balanced salt solution through the needle as seen in Figure 77-9D. This will help delineate the tissue planes and enhance dissection as well as reduce the likelihood of cutting the superior rectus muscle. In this case, the conjunctiva lifts off the plaque that covers the prior filtration site. However, it is very adherent to the underlying fibrous tissue near the limbus (Fig. 77-9D). Use a Weck-cell sponge to massage the subconjunctival fluid towards the scarred conjunctiva that requires elevation (Fig. 77-9E). This hydrodissection was successful, helping to prevent a buttonhole during limbal dissection.

Rotate and insufflate.• (C) The globe is rotated

downward to expose the superior conjunctiva. A 30-gauge needle attached to a syringe with balanced salt solution is inserted into the conjunctiva in order to insufflate the tissue. This separates the conjunctiva from surrounding Tenon’s capsule, making it easier to initially dissect the conjunctiva from the underlying connective tissue.

Insufflate the conjunctiva.• (D) Roughly 10 mm posterior to the limbus,

insufflate the conjunctiva with balanced salt solution. The fluid forces the conjunctiva to elevate, separating it from underlying scar tissue making the dissection easier. This technique aides in dissection and alerts the surgeon to areas of scarring and areas prone to a buttonhole in the conjunctiva. The conjunctiva does not elevate at approximately 3 mm from the limbus, where it was very adherent to underlying Tenon’s (black arrow). The benefit of this posterior incision is that Tenon’s capsule begins to thicken. A thick Tenon’s capsule is vital for a watertight conjunctival closure. Some surgeons will close the Tenon’s layer first followed by the conjunctival layer.

Pressure with a Weck-cell sponge.

• (E) Pressure with a Weck-cell sponge on the surface of the bleb spreads and elevates the more adherent conjunctiva from the underlying scar tissue. This allowed the conjunctiva to lift off the limbal area, making dissection easier. (F

CONJUNCTIVAL AND TENON’S CAPSULE INCISION • Initiate the conjunctival incision by inserting the tip of the

scissors into the conjunctival hole made by a 30-gauge needle and start dissecting conjunctiva from the underlying tissue (Fig. 77-9F and 77-9G). Retract the conjunctiva with blunt forceps (Fig. 77-9H). This exposes the underlying Tenon’s capsule. Capture the edge of Tenon’s with blunt forceps directly under the conjunctival wound edge. Dissect the fibrous coat from the episclera for the entire length of the wound while avoiding the rectus muscle. This approach typically maintains a cuff of Tenon’s capsule at the conjunctival wound margin, which will be vital for a watertight closure at the completion of this surgery.

CONJUNCTIVAL AND TENON’S CAPSULE INCISION • (F) Incise the conjunctiva.

The tip of the sharp Westcott scissors is inserted into the same hole made by the 30-gauge needle and the conjunctiva is incised (white arrow). The conjunctiva is first dissected free from the underlying Tenon’s capsule.

CONJUNCTIVAL AND TENON’S CAPSULE INCISION • (G) Extend conjunctival incision. Note

that the line of the incision is at least 10 mm posterior to the limbus. The most common error in limbal-based trabeculectomy is making the conjunctival incision too close to the limbus. Scar tissue will always pull the incision line towards the limbus as the eye heals during the first 2 months. Exercise caution during the dissection, for the superior rectus muscle is directly below the incision site. Insufflating the conjunctiva moves it away from the underlying muscle and minimizes the chance of a muscle laceration.

DISSECT CONJUNCTIVAL FLAP • Once both planes (conjunctiva and Tenon’s) of the wound margin

are exposed, grasp both with blunt forceps and dissect them together as one from the underlying sclera. There are several techniques for this, but the safest is to visualize the scissors through the transparent conjunctiva during the dissection as shown in Figure 77-9I. The only time the conjunctiva requires retraction during this dissection is when scar tissue is encountered that prevents the dissection. Use cautery sparingly to prevent necrosis and excessive tissue shrinkage (Fig. 77-9J). If excessive redundant Tenon’s is encountered during dissection, it may be cautiously and sparingly thinned and excised. A Weck-cell sponge is useful to mechanically separate Tenon’s capsule from the limbal

DISSECT CONJUNCTIVAL FLAP • A Weck-cell sponge is useful to mechanically separate Tenon’s

capsule from the limbal junction. Older patients who have thinner Tenon’s capsules require minimal manipulation to this layer, whereas younger patients who have thicker Tenon’s capsules require excision of just enough tissue to visualize the scleral flap sutures. Tenonectomy is difficult in younger patients who have redundant tissue. The best technique to avoid an inadvertent buttonhole is to visualize the tip of the scissors at all times through the semitransparent conjunctiva as the limbus is approached. It is rare today to need a tenonectomy, for compression with a suture lysis lens will show the suture during the postoperative period in most patients. As the limbus is approached, a crescent blade is useful to separate the strands of Tenon’s from the episclera.

Incise Tenon’s capsule at the wound margin.• (H) Once the edge of the

conjunctiva is exposed for its entire length (white arrow), the underlying Tenon’s capsule is apparent (blue arrow). Switch to blunt Westcott scissors and open the Tenon’s capsule, avoiding the underlying superior rectus muscle. Separating the layers facilitates a two-layer closure. Occasionally, especially in the elderly, the Tenon’s layer is very thin and difficult to dissect intact.

BLUNT DISSECTION• (I). The blunt Westcott scissors

is an excellent instrument to safely dissect conjunctiva and Tenon’s from the underlying sclera. At the wound site, grasp the cut edges of both the conjunctiva and Tenon’s and dissect the Tenon’s capsule off the episclera. During this process, maintain visualization of the tip of the Wescott scissors to avoid an inadvertent buttonhole.

Wet-field cautery• (J) Wet-field cautery and tissue

plane dissection. Excessive scleral cautery induces considerable astigmatism, especially near the limbus. The blue arrow denotes the area where the conjunctiva– Tenon’s plane is severely adherent to the episclera and unable to be dissected with blunt instrumentation. At this juncture, sharp Westcott scissors are necessary to continue dissection, as noted in the next steps.

Method for sharp dissection• (K) Method for sharp dissection with conjunctival

scarring. Sharp dissection is commonly required during revision of a trabeculectomy, but rarely needed during surgery in a primary case. Successful sharp dissection requires visualization of the tips of the scissors at all times through the transparent conjunctiva.

Method for sharp dissection• (K1) Small excursions of the tips are

used; do not open the tips widely or too much of the tissue is impaled, leading to a buttonhole. The black line outlines where Tenon’s is still adherent to the underlying tissue, tethering it down to the sclera or, in this case, a plaque of scar tissue over a preexisting filter. The black arrow denotes the anterior extent of the scissor cut. If the tissue is impaled all the way to the red arrow, a buttonhole is sure to occur because the conjunctiva is folded underneath, as in

Method for sharp dissection• (K2) This drawing shows how

a buttonhole forms when too much fibrous tissue is cut at one time during a sharp dissection. The proper way to dissect with sharp Westcott scissors is to place the tips of the scissors on the area to be incised as in the black arrows in Fig. 77-9K1 and then flip the conjunctiva back over the scissors as in

Method for sharp dissection• (K3) One must know the location

of the scissors at all times by direct visualization through the conjunctiva. This ensures that the conjunctiva is not perforated prior to closing the scissors as the tissue is dissected. The sharp dissection technique requires multiple microincisions, not a large one. As the dissection progresses, periodically and repeatedly lift the conjunctiva up to re-establish orienta

Method for sharp dissection• (K4) Careful sharp

dissection prevents buttonholes of the conjunctiva. The conjunctiva is intact and the scar tissue over the previous filter is easily seen and ready for dissection.

TECHNIQUE FOR SEPARATING CONJUNCTIVAL–FIBROUS ADHESIONS • This technique is very helpful when scar tissue is

encountered during any conjunctival dissection. The entire technique is dedicated to preventing a buttonhole in the conjunctiva. During the dissection with blunt scissors, an impasse was encountered. The arrow indicates a fibrous adhesion indicating the need for a slightly different technique.

POSTERIOR DISSECTION OF TENON’S CAPSULE • Dissecting a small pocket of Tenon’s capsule posterior to

the proposed bleb site encourages a posterior flow, and establishes a space for posterior application of MMC

Posterior dissection of Tenon’s capsule.

• (L) Separating Tenon’s from the sclera posterior to the wound margin will encourage posterior flow of aqueous and development of a diffuse bleb (blue arrow). This technique helps to prevent cystic blebs that tend to migrate anteriorly. The dissection should be carried out on both sides of the superior rectus muscle, which is not violated during this dissection.

ANTIMETABOLITE • In general, it is better to err on the side of too little

antimetabolite. The reason is simple: once applied, you can’t take it back. In virgin eyes with a low risk of failure, some physicians do not use an antimetabolite (although this trend is becoming increasingly rare). In this revision, MMC was used as noted

(M) Subconjunctival application of mitomycin C.• (M1) Antimetabolites are

especially important on filter revisions where there is increased tendency for scarring. Notice the pledget is pushed posteriorly to the premade subconjunctival pocket

(M) Subconjunctival application of mitomycin C.• M2) This drawing shows the typical

placement pattern for the sponges, three in this case. The authors prefer this placement pattern for fornix or limbal filters. Currently, the pledgets are placed posteriorly in order to encourage flow away from the limbus. Excessive flow directly over the fistula is more likely to cause the bleb to become pale and avascular. The dose is 0.2 mg/mL for 3 minutes for most cases. When performing a combined cataract and trabeculectomy, one may consider increasing the MMC exposure time and/or concentration. After the MMC is removed, the area is profusely irrigated.

PARACENTESIS. • A paracentesis is critical to judging the characteristics of

the filter during surgery (Fig. 77-9N). In addition, the paracentesis track may be accessed postoperatively, making it easier to enter the anterior chamber in a soft eye. It may be easier to make the paracentesis in a virgin eye after the flap is dissected anteriorly, as flap creation is much easier in a normo- tensive environment as opposed to a hypotensive environment.

Paracentesis.• (N) The corneal paracentesis is

imperative in filtration surgery. It helps determine the flow through the scleral flap. Once the conjunctiva is closed, the anterior chamber is insufflated through the paracentesis, allowing one to check for bleb leaks. The paracentesis is made with a supersharp blade. Stay parallel to the iris plane, make sure the blade is sharp, and gently enter the anterior chamber, avoiding the iris and lens. (

REMOVAL OF SCAR TISSUE FROM PRIOR FILTER. • Scar tissue assumes various forms associated with prior

filtration surgery. In this case, a fibrous cap formed over the filter required removal in order to gain access to the sclera

(O) Removal of fibrous cap over prior trabeculectomy site.• (O1) The back wall of the

fibrous capsule is incised and dissected off the sclera.

(O) Removal of fibrous cap over prior trabeculectomy site.• (O2) The blue arrow

indicates the fibrous capsule as it is dissected anteriorly. The green arrow is the conjunctiva–Tenon’s plane retracted forward.

(O) Removal of fibrous cap over prior trabeculectomy site.• (O3) Removal of fibrous

cap that caused the filter to fail. This is typical for a trabeculectomy revision, which technically is more difficult than a virgin trabeculectomy.

FASHION FLAP • For the development of a standard flap, refer to Figure

77-7I–P. There is no difference in flap-making for either a limbus- or a fornix-based procedure. The trapezoidal flap is favored during fornix-based surgery due to its shape, with less posterior space requirement.

REVISE SCLERAL FLAP • If the flap is thick and intact, revision is relatively easy

and the flap can be simply resutured back to the sclera as in Figure 77-7AA. However, in most revisions, the scleral flap is thin and accessible at only one point. In this case, a sharp blade was used to incise the old border, and a cyclodialysis spatula slid into the anterior chamber to reestablish flow (Fig. 77-9P). The flap is then closed to allow some aqueous flow.

(P) Scleral incision and wound revision• (P1) Reopen the flap with

a supersharp blade down almost to the level of the choroid. This is only necessary in one area, as trying to dissect a thin flap will cause it to tear, necessitating a patch graft.

(P) Scleral incision and wound revision• (P2) Slide a cyclodialysis

spatula through the opening to make sure debris does not clog the old trabeculectomy stoma. At this time, aqueous once again will start to flow through the fistula. The spatula is carefully inserted under the scleral flap and guided into the area of the stoma. (P3

(P) Scleral incision and wound revision• (P3) Advance the cyclodialysis

spatula into the anterior chamber to ensure flow (green arrow). Do not force the spatula into the anterior chamber: it should be an easy entry. Excessive force implies the unseen tip of the spatula is in the wrong position. If the scleral flap during a revision is thick and easy to dissect, this maneuver is not needed, for the entire old gap may be dissected, revealing the old stoma.

FLAP CLOSURE • The general principle of flap closure is to avoid a

through-and-through hole in the scleral flap while closing it. This principle holds for all types of scleral flap closure

(Q) Scleral flap closure• (Q1) The goal is to

reapproximate the scleral flap so there will be controlled leakage of aqueous through the cut edge of the flap.

(Q) Scleral flap closure• (Q2) In this revision, the

sclera is thin, which is the more common finding during a revision. The suture, typically a 10-0 nylon cutting needle, is passed through the flap at a depth of two-thirds thickness.

(Q) Scleral flap closure• (Q3) If the needle track goes

all the way through the sclera, a leak may occur directly through the needle track leading to uncontrolled flow through this site. This may be a problem, especially if the suture cheesewires through the sclera when the suture is tied, making the hole larger. On thin flaps, use 10.0 nylon on a tapered needle; it creates a smaller scleral hole. (

WOUND CLOSURE• The guiding principle in all filtration wound closures is a

watertight finish. In this case a double-layer closure is used, a routine for all limbus-based procedures. The double-layer closure guarantees a watertight wound

(R) Double-layer closure: closure of Tenon’s capsule and conjunctiva.• (R1) A double-layer

closure is an added security against postoperative leaks. First, Tenon’s is isolated and an 8-0 braided polyglactin suture tied to it.

(R) Double-layer closure: closure of Tenon’s capsule and conjunctiva.• (R2) This is a running,

locking suture. The lock can be seen at the green arrow. Tenon’s tissue acts as a gasket to prevent leaks.

(R) Double-layer closure: closure of Tenon’s capsule and conjunctiva.• (R3) Tenon’s may be periodically

incorporated into the conjunctival closure if it looks like the conjunctival tissue is redundant. This tags the conjunctiva and pulls it posteriorly, preventing an overhanging postoperative bleb. A 10-0 polyglactin monofilament suture is used to close the conjunctiva in a watertight fashion. The suture is tightened as it is tied to assure a tight closure. The knot is trimmed to prevent postoperative irritation.

WOUND TEST FOR BLEB INTEGRITY• Use the paracentesis site to inject balanced salt solution

into the anterior chamber; the bleb should insufflate (Fig. 77-9S). Check for leaks and repair as necessary. If a leak is discovered, use a 2850 nylon tapered needle (Ethicon) to close the leak. This is a very small needle that creates only a small opening in the conjunctiva when passed through. The eye looked very good on postoperative day 1

(S) Insufflate and check for leaks.• (S1) The anterior chamber is

insufflated with balanced salt solution through the paracentesis track. Carefully position the 30-gauge cannula into the chamber in order to prevent Descemet’s detachment. The bleb should rise as the fluid is injected, if not, there is a leak or the flap is too tight.

(S) Insufflate and check for leaks.• (S2) Dry the conjunctival

closure with a Weck-cell sponge in order to check for leaks. Leaks are easy to spot with this technique and easy to miss without this technique. Recheck the bleb and remove the traction suture. (

Postoperative day 1.• (T) The anterior chamber

is deep, the cornea clear, and the eye is quiet. A nicely elevated bleb without wound leak is present on day 1. The IOP is lower than anticipated at 3 mmHg, but fortunately resolved without complications a week later.

Complications of Trabeculectomy

Intraoperative Complications of Trabeculectomy • Trabeculectomy is performed to achieve lower

intraocular pressure by creating a surgical fistula to increase aqueous outflow into a conjunctival bleb. In spite of a well-performed procedure, the final outcome is unpredictable due to variable and unknown factors in wound healing leading to bleb failure. The margin of error in performing trabeculectomy is very small.

Intraoperative Complications of Trabeculectomy • Every effort should be made to avoid intraoperative

complications. The surgeon should learn and modify his or her techniques to strive for perfection. However, if intraoperative complications occur, one should be able to recognize them and take appropriate action at the time of surgery. Some of the important precautions during surgery are: ■ Avoid subconjunctival hemorrhage by using a corneal traction suture instead of a superior rectus traction suture.

Intraoperative Complications of Trabeculectomy • ■ Handle conjunctiva carefully by using nontoothed

forceps or Weck-cel sponge for dissection. Keep it moist to avoid shrinkage. ■ Obtain good hemostasis by using pencil-tip cautery in the deep scleral bed and on the scleral surface but away from the scleral flap margin. ■ Always look for buttonholes and wound leaks. The anterior chamber should be maintained with balanced salt solution and not a viscoelastic at the conclusion of the surgery.

management of the patient• The long-term success of trabeculectomy depends in part on

the preoperative and intraoperative management of the patient. Any intraoperative complication, if not properly managed, will lead to failure. Similar to any other operation, trabeculectomy can be complicated by problems such as anesthetic issues, poor surgical technique, intraocular hemorrhage, and postoperative infection. It is estimated that 50–60% of patients suffer some level of surgical complication with trabeculectomy.1,2 Most of these are minor and only require careful observation and follow-up, but some can lead to ultimate failure of filtration surgery and/ or permanent vision loss.

management of the patient• In the majority of cases, the surgeon seeks to achieve

an initial watertight wound closure with gradual release of the scleral sutures to regulate the extent of subconjuctival aqueous outflow. However, the delicate balance between outflow and healing may be tipped too far in one direction or the other, thereby leading to either hypotony or surgical failure of the bleb. The surgeon may attempt to minimize the unpredictability of the postoperative course by ensuring meticulous intraoperative technique.

Intraoperative Complications• ■ Traction suture • ■ Hematoma in superior rectus muscle • ■ Severing of superior rectus tendon • ■ Cheese wiring of cornea • ■ Corneal perforation • ■ Conjunctival flap • ■ Mishandling of conjunctiva • ■ Conjunctival buttonhole/tear • ■ Subconjuctival/episcleral bleeding

Intraoperative Complications• ■ Mitomycin sponge application • ■ Retained mitomycin sponge after surgery • ■ Conjunctival buttonhole/tear by sponge • ■ Scleral flap dissection • ■ Improper thickness of superficial flap • ■ Disinsertion of the superficial flap • ■ Inadvertent early entry into anterior chamber • ■ Incomplete removal of Descemet’s membrane

Intraoperative Complications• ■ Sclerostomy • ■ Inadequate/incomplete fistula formation • ■ Iris/cornea/lens injury • ■ Corneal injury • ■ Abrasion and epithelial defect • ■ Descemet’s membrane detachment • ■ Iridectomy-related • ■ Incomplete iridectomy • ■ Large iridectomy • ■ Iris incarceration/prolapse • ■ Iris bleeding/anterior chamber bleeding (hyphema) • ■ Iridodialysis

Intraoperative Complications• ■ Others • ■ Lens injury • ■ Ciliary body injury • ■ Cyclodialysis • ■ Vitreous loss • ■ Shallow anterior chamber • ■ Conjunctival wound leak • ■ Serous choroidal detachment • ■ Suprachoroidal hemorrhage.

Late Failure of Filtering Bleb

Late Failure of Filtering Bleb• Late failure of filtration has several causes that range from

blockage of the internal ostium to remodeling of the filtering bleb to frank scarring of the bleb. Identifying the cause makes management clear and likely to be successful. Bleb remodeling occurs within the first 3–4 months following filtration surgery and can often be managed conservatively as it may be transient. Scarring of the episclera with loss of bleb function may occur anytime from weeks to months or even years after the initial surgery. Needling using loupes or at the slit lamp is often successful in this situation and is a worthwhile in-office treatment to try. Sometimes, operative revision of the filtration bleb or repeat filtration at an alternate site is necessary if needling fails.

DRAINAGE DEVICES

Preoperative Evaluation • The ultimate goal to be wished for with the use of a

glaucoma implant is pressure lowering. Most studies reported in the literature, with the use of glaucoma implants, define success as pressures of 21 mmHg or lower. Most severe glaucoma cases, and this usually includes most cases in which a glaucoma implant will be used, require pressures in the low teens, a level often difficult to obtain with glaucoma implants. The pressure-lowering effect of the implant depends on the thinness and permeability of the bleb over the plate. This can be achieved with the use of antifibrosis medication, e.g. systemic steroids, or by modification of the surgical technique, e.g. supra-Tenon’s plate placement.

Preoperative Evaluation • Therefore, preoperatively, if a very low pressure needs

to be achieved, the feasibility of the use of systemic medications such as steroids and non-steroidal anti-inflammatories needs to be considered. Should the patient have any medical condition or conditions precluding systemic antifibrosis medication use, such as diabetes or hypertension, then modification of the surgical procedure needs to be considered, and this will always include the choice of implant to be used. Supra-Tenon’s placement always needs a single-plate implant, the ideal size being the single-plate Molteno implant.

Introduction • In deciding on the use of glaucoma implants for the

management of uncontrolled intraocular pressure, a number of important factors need to be taken into consideration. These factors may be summarized as follows: • 1. The underlying cause of the glaucoma. • 2. The anatomy of the eye and orbit under

consideration. • 3. Age and ethnicity of the patient.

Introduction • 4. Previous surgical procedures done in the eye, as well

as any additional pathology that may be present, such as cataracts or corneal disease. • 5. Choice of implant, which incorporates the final

intraocular pressure desired to be achieved.

DRAINAGE IMPLANTS• Drainage implants were originally introduced to treat refractory

glaucomas.2 These included aphakic and pseudophakic glaucomas, uveitic glaucoma, neovascular glaucoma, glaucoma associated with corneal transplants, congenital glaucomas due to iridocorneal dystrophies such as iridocorneal endothelial dystrophy, and in eyes where previous filters had failed. With the introduction of the use of antimetabolites, such as 5-fluorouracil and mitomycin C, many of the conditions mentioned in this group are now treated with conventional filtering surgery first. Exceptions include neovascular glaucoma, extensive scarring of the conjunctiva, and congenital glaucoma with iridocorneal dysgenesis or with previously failed goniotomy or trabeculotomy. Aphakic glaucoma and glaucoma associated with corneal transplants also do better with glaucoma implants. The 3-year follow-up comparing tube shunt surgery to trabeculectomy in pseudophakic patients showed a higher success rate with tube shunts

Choice of Implant • The questions to be asked regarding the choice of

implants are: • 1. Do all implants lower the pressure equally,

irrespective of their design? • 2. Does size matter? • 3. What important complications are associated with the

different implant?

Choice of Implant • The overall success rate among five implants studied,

namely, Molteno single and double plate, Baerveldt, Ahmed, and Krupin implants, was between 72% and 79%. All five implants decrease the pressure by 51–62%. There were no statistically significant differences in either the percentage change in intraocular pressure (IOP) or the overall surgical success rate among the five implants, or within the subdivisions of the Molteno group based on the size of the end plate.

DOES SIZE MATTER? • The original single-plate and double-plate Molteno

implants are now rarely used. Newly designed larger single-plate Molteno implants are now preferably used. The new single-plate Molteno 3 implant comes in two sizes, 185 mm2 and 245 mm2. The single-plate Ahmed and Krupin implants are equal at184 mm2. The Baerveldt implant comes in two sizes, namely 250 mm2 and 350 mm2, the latter being the same size as the double-plate Ahmed implant double-plate.

DOES SIZE MATTER? • The advantages of choosing a small implant are ease of

insertion and that only a single superior quadrant of the eye is used, leaving the other quadrant available for a second implant if necessary. A prospective study comparing the pressure-lowering effect of single- and double-plate implants confirmed the theory that larger plates lower the pressure to a greater extent. Perhaps larger plate size does not result in better IOP control in the long term, and the standard size single-plate implant, which is almost identical in the different implants available, other than the Baerveldt which is larger, may all have a similar pressure-lowering potential

PLATE MATERIAL • The Molteno plate consists of polypropylene, whereas

the Ahmed is either polypropylene or smooth silicone. The Baerveldt plate is silicone.

COMPLICATIONS • Postoperative hypotony is a major concern and,

therefore, a decision to prevent this from occurring needs to be made. The choices are valved or non-valved implants. The major advantage of valved implants (e.g. Ahmed, Krupin) is less postoperative hypotony in most cases, although valve failure can occur, resulting in hypotony. The major disadvantage of the valved implants is a more intense hypertensive phase, with a thicker bleb and less pressure lowering in the long term. Stenting of the tubes in non-valved implants may be done to prevent postoperative hypotony.

Aqueous Shunts: Choice of Implant • Since publication of the Tube vs. Trabeculectomy Study

there has been increased interest in the use of aqueous shunts for the management of glaucoma. Evidence suggests that long-term IOP control after aqueous shunts is determined, not only by the size of the end-plate on the shunt, but also on plate material, profile and surface texture. Two of the most commonly used implants are the Ahmed Glaucoma Valve and Baerveldt Glaucoma Implant. They differ in that the former has a flow restrictor to minimize early hypotony, and the latter has a large, smooth flexible plate to minimize encapsulation.

Baerveldt 350 implant• Evidence from two recent randomized trials suggests

that the Baerveldt 350 implant gives lower pressures with fewer glaucoma medications after 1 year, but at the cost of slightly more complications. Longer-term data from these trials are awaited at the time of writing.

BASIC PRINCIPLES• The basic principles of shunt function include a

permanent sclerostomy, i.e. a tube, usually made of silicone, placed into the anterior chamber, ciliary sulcus or vitreous cavity, that drains aqueous to the equatorial sub-Tenon’s space. To maintain long-term patency of the distal aperture of the tube, the opening is surrounded by a plate, usually made of silicone, of a predetermined surface area. This plate gradually becomes encapsulated by surrounding tissue in the weeks after surgery, resulting in resistance to aqueous flow.

principal problems• The two principal problems with shunts are firstly, that

the shunt may drain too rapidly in the early postoperative period, before this capsule develops. Secondly, the capsule may restrict the absorption of aqueous to such an extent that the intraocular pressure (IOP) is not sufficiently well-controlled.

CHOICE OF SHUNT• Factors that might influence the choice of shunt in the

individual patient include shunt-related factors such as those that influence the impact of encapsulation, such as plate surface area and plate material, and those that affect early IOP control, such as the presence or absence of a flow resistor. Patient factors include the type of glaucoma, the likelihood of hypotony, the presence of impediments to implantation, such as scleral buckles, and factors that may influence the degree of scarring, such as anterior segment neovascularization.

VALVED VERSUS NONVALVED • One of the most important features of a shunt is the

presence or absence of a flow restrictor (valved or nonvalved). Although the flow restrictors in the former group have not been shown to actually function as valves, the name has nevertheless stuck. Valved devices, in theory, allow only unidirectional flow with a minimum opening pressure, whereas nonvalved devices are passive, incapable of influencing flow.

VALVED VERSUS NONVALVED • The Ahmed Glaucoma Valve is an example of the former,

whereas the Molteno Implant and Baerveldt Glaucoma Implants are examples of the latter. These implants have a similar lumen diameter (approximately 300 μm). Without a valve, this diameter of tube offers virtually no resistance to flow and can drain the anterior chamber completely of aqueous relatively quickly. • This does not occur in the early postoperative period with

valved implants because the integral flow restrictor prevents hypotony in most cases.16,17 With the Ahmed, the implant must be primed with a fluid such as balanced salt solution (BSS) in order to separate and wet the valve leaflets.

VALVED VERSUS NONVALVED • Nonvalved shunts do not contain a flow restrictor and must be

occluded effectively by the surgeon at the time of implantation, to avoid severe hypotony. A number of techniques have been described to prevent early hypotony with nonvalved aqueous shunts. The most commonly used at the time of writing is external ligation with an absorbable ligature such as 7/0 polyglactin 910 (Vicryl, Ethicon, Johnson & Johnson International, Brussels, Belgium). No method has yet been described that will permit aqueous flow to be successfully titrated to a clinically safe level with a ligature. The purpose of ligation is therefore to occlude the tube completely. Failure to achieve complete occlusion may result in severe hypotony.

VALVED VERSUS NONVALVED • Successful ligation often results in a high IOP and, to

counteract this, many surgeons additionally fenestrate the tube proximal to the ligature (Sherwood slit).18 • A further disadvantage of external ligation is sudden

decompression, usually 5–6 weeks after surgery when the ligature absorbs. Even if sufficient encapsulation has developed, the precipitous drop in pressure in eyes with larger implants, such as the Baerveldt 350, may be sufficient to cause a choroidal hemorrhage in a predisposed individual

THE AHMED GLAUCOMA VALVE • This implant (Fig. 110-1) is manufactured with a flexible

silicone plate (FP7) or a rigid polypropylene plate (S2) of similar surface area (184 mm2). The tube portions are identical and approximately 23-gauge in external diameter. Versions with smaller plates designed for pediatric eyes are also available.

AGV contains a valve mechanism which must be primed prior to insertion.

THE BAERVELDT GLAUCOMA IMPLANT • This implant features a large (250 or 350 mm2) flexible silicone

plate that is noticeably different from the Ahmed, in that it is thinner, broader, and barium-impregnated rendering it radio-opaque. The wings of the 350 mm2 implant are usually placed under adjacent rectus muscles. In order to avoid interference with muscle function, they are often placed about 1 mm behind the muscle insertion, and the plate is secured tightly to sclera to avoid movement.

• It is also possible to implant the Baerveldt 101-350 with the wings on top of the muscles and this is sometimes performed in patients with extensive scarring, most commonly after retinal surgery. The 250 mm2 implant has smaller wings which are not usually tucked under the muscles.

The arrow shows infused BSS flowing and demonstrates the large plate surface area

SURGICAL TECHNIQUE • The basic surgical technique is similar for all GDDs (Figure 8). They differ in respect to: • Size of the conjunctival incision • Methods of flow restriction • Anterior chamber or pars plana insertion of the tube.

Surgical Technique 1 (Molteno )

Molteno implants• Molteno implants (Molteno Ophthalmic Limited, Dunedin, New

Zealand) are surgical devices used in the treatment of severe and complex cases of glaucoma. They were developed by Anthony C.B. Molteno and consist of a fine-bore silicone tube that delivers aqueous from within the eye onto the surface of an episcleral plate (Fig. 111-1). The plate is covered by Tenon’s fascia and conjunctiva, and initiates and maintains a large circular unilocular bleb. The bleb develops a specialized fibrovascular lining called the bleb capsule that becomes distended by aqueous. The bleb capsule is responsible for regulating aqueous escape from the eye and is the main determinant of the final intraocular pressure (IOP) achieved by the draining implant.

HYPOTENSIVE, HYPERTENSIVE, AND STABLE STAGES • The changes that accompany bleb formation around an

implant are most obvious when a single-plate implant is used to drain severe and advanced glaucoma in a young adult. Three sequential stages are described according to the behavior of the IOP after implant insertion

1. Hypotensive stage • This stage lasts 7–10 days after operation and is

characterized by low IOP with diffuse edema and congestion of blood vessels in the tissues covering the episcleral plate of the implant.

2. Hypertensive stage: • This stage is characterized by elevated IOP that peaks

at 30–50 mmHg 4–5 weeks after operation (in untreated cases). As the edema subsides, a definite layer of fibrous tissue appears in the deepest layers of the bleb capsule and the bleb becomes distended with aqueous. However, it is not until the vascular congestion resolves that the IOP starts to fall, initially rapidly then more gradually, to reach a stable plateau 3–6 months after operation.

3. Stable stage: • Characterized by a stable IOP and well-circumscribed

bleb with a moderately vascular fibrous bleb capsule, the stable-stage bleb remains unchanged for the remainder of the patient’s life. The thickness of the capsule depends on the intensity and duration of bleb inflammation during the hypertensive stage. Trials of anti-inflammatory fibrosis suppression therapy were undertaken in an effort to limit inflammation and produce a thin permeable bleb capsule.

Indications• Molteno implants are considered in cases where simple drainage operations

such as trabeculectomy are unlikely to provide safe long-term IOP control. Current indications for using implants include:

• 1. Infantile and juvenile glaucoma.• 2. Aphakic or pseudophakic glaucoma.• 3. Traumatic glaucoma.• 4. Uveitic glaucoma.• 5. Glaucoma secondary to previous intraocular surgery.• 6. Neovascular glaucoma.• 7. Failed previous trabeculectomy .• 8. Complications of trabeculectomy on the fellow eye.• 9. Patients intolerant of, or who cannot cooperate with, the medication regimen.

Molteno3 implant• Since 2004, evaluation of the Molteno3 implant

suggests that the 175 mm2 Molteno3 implant should be used in all cases except young patients and larger eyes in which the 230 mm2 Molteno3 implant is preferred

CHOICE OF SURGICAL TECHNIQUE• DELAYED VERSUS IMMEDIATE DRAINAGE OF AQUEOUS.

Molteno implants can be inserted for delayed or immediate drainage of aqueous. The advantages of delayed aqueous drainage are such that the Vicryl tie technique is almost always used. Immediate drainage of aqueous, however, is necessary in acutely inflamed eyes and when immediate IOP reduction is required, e.g. acute neovascular glaucoma, uveitic glaucoma and when the eye contains blood after trauma. Photocoagulation of underlying retinal disease and/or anti-inflammatory fibrosis suppression therapy can be used to minimize the resulting hypertensive stage.

CHOICE OF SURGICAL TECHNIQUE• Delayed drainage allows time for tissues to heal and form a thin

bleb capsule (preformed bleb) around the implant. During this time the IOP is controlled either with hypotensive medication or by making a relieving Sherwood slit in the side of the translimbal tube at the time of operation.6 The slit functions as a safety valve and releases aqueous if the IOP rises above normal levels. It ceases to function about 4 weeks after operation as the Vicryl tie dissolves and the tube opens allowing drainage of aqueous into the preformed bleb. This avoids postoperative hypotony, reduces the inflammatory response that occurs at the onset of aqueous drainage and results in a thinner bleb lining with superior long-term IOP control

QUADRANT SELECTION • The superior nasal or superior temporal quadrants are preferred.

Tenon’s fascia is thicker in the superior nasal quadrant and minimizes the chance of late tube erosion through conjunctiva. Surgical exposure, however, is better in the superior temporal quadrant.

• The inferior quadrants may also be used when superior quadrant access is limited. The inferior temporal quadrant is preferred in order to minimize the risk of diplopia that may occur in patients with good vision in both eyes if the inferior nasal quadrant is used.

• In eyes containing silicone oil, the implant can be placed superiorly or inferiorly. Any silicone oil entering the tube drains to the bleb, and silicone oil that rarely blocks the ostium can be cleared with neodymium:YAG laser.

TRANSLIMBAL VERSUS PARS PLANA INSERTION. • In most cases, the tube is inserted into the anterior

chamber. Pars plana tube insertion requires prior or simultaneous vitrectomy and is indicated where:• 1. The cornea is compromised or opaque;• 2. The anterior chamber is too shallow or nonexistent to

permit insertion of the tube between iris and cornea;• 3. A vitrectomy has been performed or is planned; or• 4. Damage to the anterior segment precludes safe

translimbal drainage.

SURGICAL TECHNIQUE FOR IMPLANT PLACEMENTPart 1. Translimbal Insertion

STEP 1. THE INCISION. • A sufficiently large fornix-based flap must be raised so

that the plates of the implant are well covered by Tenon’s fascia and conjunctiva (Fig. 111-5 and Video 111-1). Using nontoothed forceps and Westcott scissors, make a perilimbal incision through conjunctiva and Tenon’s fascia with radial cuts backward at each end in order to expose sclera and the rectus muscle insertions in the appropriate quadrant(s). Cauterize any bleeding points.

STEP 2. GLOBE FIXATION. • Pass 4/0 silk sutures under the rectus muscles adjacent

to the selected quadrant and attach to the drape to fix the eye in position. Using the handle of a scalpel, gently push Tenon’s fascia posteriorly to expose sclera for 2–3 mm behind the rectus muscle insertions.

STEP 3. RAISING THE LAMELLAR SCLERAL FLAP • When the sclera is of adequate thickness, dissect a

limbal-based half-thickness lamellar scleral flap anteriorly until it extends 1 mm into clear cornea (Fig. 111-6). From posterior to anterior, this demonstrates opaque white sclera then a subtle translucent area marking the position of Schlemm’s canal followed by an opaque white line indicating the edge of Descemet’s membrane (Schwalbe’s line). Where sclera is very thin, omit the dissection and cover the tube with a piece of donor sclera after inserting the tube into the anterior chamber

STEP 4. POSITIONING THE IMPLANT • Position the implant so that the anterior edge of the

plate lies symmetrically between the rectus muscles, in order to minimize any interference with the action of the muscles and avoid diplopia (Fig. 111-7). For double-plate implants, either pull the second plate through underneath the superior rectus muscle or place the connecting tube over the muscle. Check that the plate can be easily covered by Tenon’s fascia. Any difficulty doing this implies a fold of Tenon’s fascia is caught behind the plate and must be freed using nontoothed forceps and applying gentle forward traction

STEP 4. POSITIONING THE IMPLANT • Pass a 7/0 silk suture posteriorly through sclera at the

rectus muscle insertion, from below up through the anterior suture hole in the plate then return the suture through sclera at the muscle insertion in a posterior to anterior direction (mattress suture). Pull the suture tight and tie a knot. Repeat this suture on the other side of the plate. The plate should now be firmly fixed to the sclera just behind the rectus muscle insertions.

STEP 5. OPTIONAL TEMPORARY TUBE OCCLUSION WITH A VICRYL TIE. • Tie a 5/0 Vicryl ligature around the tube of the implant

close to the episcleral plate using two half hitches to form a slip knot, pull the knot tight and lock it with a third throw (Fig. 111-8). Exercise care when tightening the suture as it can cut through the silicone tube or pull the tube off the plate if excessive force is used. Using a 2 mL syringe and Rycroft cannula, inject saline up the tube to test that the tube has been completely occluded. Place a second throw to lock the knot and cut the suture ends 3–4 mm long to prevent the knot untying itself.

STEP 6. TRIMMING THE TUBE. • In order to trim the tube to the correct length, replace

the lamellar scleral flap and lay the tube over it so that it overlaps the cornea. Using spring scissors and taking care not to stretch the tube, trim the end 2 mm beyond the limbus at an angle of 45° with the bevel facing forward. The tube will then extend into the anterior chamber to the correct distance of 3 mm after insertion beneath the scleral flap.

STEP 7. INSERTING THE TUBE INTO THE ANTERIOR CHAMBER. • The anterior chamber must have sufficient depth to allow

placement of the tube without compromising the corneal endothelium. If it does not, the tube should be placed into the posterior chamber.• Make an entry track into the anterior chamber using a 22-gauge

needle with the distal two-thirds of its bevel bent forwards at 30° to produce a microkeratome with a hollow blade. Bending the needle flattens it slightly so that its diameter is greater than the tube. Some surgeons prefer to use an unmodified 23-gauge needle. Hold the microkeratome blade parallel to the plane of the iris and insert it into opaque sclera 1–1.5 mm posterior to the translucent zone that marks the position of Schlemm’s canal

STEP 7. INSERTING THE TUBE INTO THE ANTERIOR CHAMBER. • tapered incision slightly larger than the tube externally and a close

fit internally. When aqueous appears on its hollow surface, withdraw the needle. Insert a Rycroft cannula through the incision to ensure correct entry into the anterior chamber, and then insert the bevelled free end of the tube along the track (Fig. 111-10). It should enter easily at first and show slight resistance as it is pushed into the anterior chamber.

• If difficulties are encountered, reinsert the microkeratome further to enlarge the tapered track. Then advance the tube into the anterior chamber and move it slightly to check that the free end is appropriately positioned (Fig. 111-11). If the tube is too anterior, withdraw it and make a slightly more posterior incision immediately behind the first incision.

STEP 8. OPTIONAL SHERWOOD SLIT • In cases where the preoperative IOP cannot be reduced

to near-normal levels by intensive hypotensive medication, a temporary valve is used. A linear slit in the tube in front of the Vicryl tie allows aqueous to escape beneath the lamellar scleral flap for several weeks until scar tissue around the tube stops aqueous drainage through the slit. By this time, the Vicryl will have dissolved allowing aqueous to drain into the preformed bleb capsule.

STEP 8. OPTIONAL SHERWOOD SLIT • To make the Sherwood slit, place the tube into the

anterior chamber then pass a 30° micropoint blade into the side of the tube parallel to the scleral surface. Advance the blade to make a linear slit that is as long as the tube is wide (Fig. 111-8). This short slit allows aqueous to escape from the tube when the IOP reaches 20–25 mmHg.• It is tempting to make the slit at the time the Vicryl tie is

placed.

STEP 9. COVERING THE TUBE • Reposition the lamellar scleral flap over the tube, and

suture loosely in position using interrupted 7/0 silk sutures, one each side of the flap. The tension of these sutures can be used to adjust the angle of the tube, if necessary. In many cases, the flap can be left unsutured and held in position by Tenon’s fascia that is sutured to sclera at the limbus.

STEP 10. CLOSURE OF TENON’S FASCIA AND CONJUNCTIVA• STANDARD CLOSURE. It is important to ensure that

Tenon’s fascia has not been caught behind the posterior edge of the plate and that it lies freely over the limbus of the eye. If caught, carefully lift and free the tissues. Once satisfied that the tissues can be easily apposed, suture Tenon’s fascia and conjunctiva at the limbus using 2–3 interrupted 7/0 silk sutures

Surgical Technique (Ahmed Glaucoma Valve Drainage Implant)

The Ahmed Glaucoma Valve• The Ahmed Glaucoma Valve is designed to drain aqueous humor

from the anterior chamber through a silicone tube and across flow-resistant valve mechanism, and then onto a silicone or polypropylene plate located posterior to the limbus. The incorporation of a flow-resistant valve in the design of the Ahmed Glaucoma Valve distinguishes this implant from other open-tube designs, including the Baerveldt and Molteno implants. During the early postoperative period, the valve mechanism may minimize the incidence of hypotony and its associated complications, such as choroidal effusions, shallow or flat anterior chamber, and suprachoroidal hemorrhage. Vision-threatening complications are uncommon after Ahmed Glaucoma Valve implantation.

Surgical Technique • Local anesthetic is administered, which may be

retrobulbar, parabulbar, or peribulbar. A 6/0 silk or polyglactin traction suture on a spatulated needle is placed through the corneal stroma adjacent to the quadrant chosen for implantation and the eye is rotated to achieve maximal exposure The Ahmed Glaucoma Valve is most often placed in the superotemporal quadrant and the plate positioned approximately 8 mm posterior to the limbus. Care should be taken when implanting in the superonasal quadrant because of proximity of the plate to the optic nerve and risk of inducing a Brown’s syndrome.

Surgical Technique • In the chosen quadrant, a fornix-based incision is made

through the conjunctiva and Tenon’s capsule. Radial relaxing incisions on one or both sides of the conjunctival flap are often added to improve surgical exposure. Blunt scissors are used to dissect between the episclera and Tenon’s capsule. Gentle blunt dissection continues posteriorly under Tenon’s capsule to create a pocket between the rectus muscles. Wet-field cautery is often used near the limbus to achieve hemostasis.

Surgical Technique • Prior to implantation, the implant should be examined

and primed (Fig. 113-3). The device’s sterilization process may cause the valve membranes to adhere to one another. Intraoperative priming of the valve with balanced salt solution though a 27- or 30-gauge cannula ensures the patency of the valve mechanism. • The anterior edge of the plate is grasped manually or with

non-toothed forceps and inserted into the pocket between the rectus muscles (Fig. 113-4). Care should be taken not to touch the valve mechanism with instruments during insertion, as this may damage the device

Surgical Technique • The valve is positioned 8–9 mm posterior to the limbus, and the

plate is anchored to the sclera with 8/0 nylon, 9/0 nylon, or a similar permanent suture on a spatulated needle though the openings on the anterior edge of the plate. The drainage tube is extended over the cornea and then cut to a length which will allow the tube to extend 2–4 mm into the anterior chamber (Fig. 113-5). A 23-gauge needle is then used to make a track beginning approximately 0.5 mm posterior to the limbus and extending into the anterior chamber parallel to or angling slightly forward of the iris plane (Fig. 113-6). Some surgeons inject viscoelastic as the needle leaves the eye in order to lubricate this needle track. The 23-gauge track is an appropriate size to allow tube entry but minimize leakage around the tube

Surgical Technique • Entry into the anterior chamber posterior to Schwalbe’s

line and anterior to the iris plane will minimize the risk of contact with the cornea or iris. The drainage tube is inserted into the anterior chamber through the needle track using non-toothed forceps or a specially designed tube inserter (New World Medical, Inc., Rancho Cucamonga, CA) (Fig. 113-7). The tube is then loosely secured to the sclera using a single procedure to reform the anterior chamber with balanced salt solution, if necessary

Surgical Technique • Subconjunctival steroids and antibiotics are injected in a

quadrant, preferably 180° away from the plate. Depending on the type of anesthesia used, an ointment containing antibiotic and steroid is applied to the eye, and it is lightly patched and shielded until postoperative day one.

Aurolab Aqueous Drainage Implant (AADI )• It is a low cost, non resistant tube device based on

Baerveldt implant. It reduces intraocular pressure by drain-ing aqueous from anterior chamber into subconjunctival space formed around base of the implant. AADI is a non-valved aqueous shunt (Figure 7) made of Nusil permanent implant silicone elastomer which has passed tissue culture cytotoxicity testing.

Aurolab Aqueous Drainage Implant (AADI )• The surface area of the AADI end plate is 350 millimeter

square and the silicone tube length is 32 millimeter. The AADI may be inserted through a 100 degree conjunctival incision. The lateral wings of the AADI are designed for positioning under the rectus muscles. The end plate is positioned between the rectus muscles and is attached to the sclera about 10 milli-meters posterior to the limbus with non absorbable sutures through the fixation holes of the implant.

Aurolab Aqueous Drainage Implant (AADI )• Temporary tube occlusion is accomplished by ligating it

with 7 zero vicryl suture. The absorb-able suture reliably lyses 4 to 6 weeks postoperatively causing spontaneous opening of the tube. A 23 gauge needle is used to make an entry incision into the anterior chamber at the posterior limbus parallel to the iris plane. The tube is inserted through the needle track, proper positioning of the tube anterior to the iris and posterior to the cornea should be confirmed. The limbal portion of the tube is covered with a donor scleral/corneal patch graft.

Aurolab Aqueous Drainage Implant (AADI )• Lower postoperative IOP is expected with capsules that

are thinner and have large surface areas. The capsule surface area is directly related to the size of the end plate. Therefore, an implant with a larger endplate produces a larger surface area of encapsulation and greater IOP reduction. The end-plate of the AADI has fenestrations that allow growth of fibrous bands reducing the profile of the bleb.

Aurolab Aqueous Drainage Implant (AADI )• The low profile of the AADI makes it particularly suitable

for infero-nasal placement as a majority of the patients posted for a drainage implant surgery have a history of one or two failed filters. Currently studies are underway to evaluate its safety and efficacy in reducing the intraocu-lar pressure and preventing further damage to optic nerve and functional visual field loss in advanced refrac-tory glaucoma.

THANK YOU

DR DINESHDR SONALEE