Ординатура / Офтальмология / Английские материалы / Glaucoma Surgery_Trope_2005

cystic blebs; a typical complaint is of a mild foreign body sensation and that the eye feels “soft.” Both these symptoms are exacerbated by blinking. Chronic epiphora can also be a problem, either because the punctum is occluded or everted by oversized blebs or because the flow of tears to the conjunctival fornix is restricted (Fig. 24.5). The relationship between the location of a diffusely draining bleb and degree of ocular irritation can be quite variable. Some eyes have 3608 of elevated conjunctiva and cause the patient little distress, whereas others with not more than 1808 of conjunctival elevation are quite symptomatic. In general, these blebs do not disrupt the tear film and are not associated with the formation of dellen. However, they can be associated with ocular hypotony if the bleb is over draining and in these cases, the management plan should, in the first instance, be directed at increasing the IOP rather than the modulation of the bleb configuration. Identification of the distribution of aqueous drainage can be difficult and careful examination is required to demarcate the extent of the bleb.

2.5.The Avascular Bleb

Finally, for some patients, the cosmetic appearance of the bleb may be an issue. In the management of elevated or diffuse blebs, this is an obvious factor for consideration. However, in eyes with low and restricted blebs, the appearance of the bleb may not be satisfactory because of the degree and distribution of conjunctival vascularity. In blebs with excessive scarring, the margin of the bleb may be demarcated by a line of increased vascularity representing a zone of excessive postoperative scarring. Within this zone, the bleb may be pale and elevated. With the increasing use of anti-scarring agents such as mitomycin C, the devascularization of the bleb can cause conjunctival pallor which may be of cosmetic concern to some patients.

2.6.Prophylaxis: Avoiding Dysmorphic Blebs

Ideally, consideration should be given to the avoidance of bleb dysmorphology when surgery is planned. The most comfortable bleb is one that is low and diffuse with a drainage area that is subtarsal. A major advance in achieving this aim has been the development of improved techniques for the delivery of agents such as mitomycin C and 5FU to minimize postoperative scarring. More recently agents such as anti-TGF beta antibodies have been introduced that show great promise in providing an optimal postoperative bleb configuration (6).

The site of the conjunctival incisions at the time of surgery may also be an important factor in determining the long-term bleb configuration. In general, diffuse low lying blebs are more frequently associated with the use of fornix based conjunctival incisions compared with limbal incisions. With fornix based incisions, anti-metabolites can be positioned subconjunctivally over a wide sector behind the filtrations site. Recent evidence suggests a lower rate of bleb related complications with fornix compared with limbal flaps in filtration surgery augmented with MMC (7). Early approaches to the application of agents such as MMC used limbal based incisions because of anxieties that compromised wound healing at the limbus would result in persistent aqueous leaks. Although the rate of wound leak was low with this approach, it often resulted in the development of thin walled cystic blebs at the corneal limbus that drained over a relatively small area of conjunctiva. These problems were particularly acute with the early use of mitomcyin C and may have accounted for the relatively high rate of postoperative endophthalmitis associated with its use.

The preferred method for the application of these agents is now to use a fornix based conjunctival flap so that the agent can be applied to a wide area of conjunctiva at away

from the corneal limbus. At the time of application, meticulous care is taken with the anterior (cut) edge of the conjunctiva to ensure that it does not come into contact with the anti-scarring agent. When the conjunctiva is sutured in place it is important to apply sutures that tension the conjunctiva at its anterior (leading) edge. In some cases, a continuous running suture can be required to ensure that the leading edge of the conjunctiva remains applied to the corneal margin. With the controlled application of mitomycin C, these simple developments have resulted in a marked improvement in the configuration of the blebs which lie low and drain diffusely (Fig. 24.1).

These blebs also have an improved cosmetic appearance as the demarcation between those parts of the bleb treated with anti-scarring agents and the untreated part can be quite diffuse. Great care has to be taken in deciding the dose of anti-scarring agent, particularly when using agents such as mitomcyin C. With prolonged application at high concentration these can result in devascularized blebs which not only place the eye at increased risks for the development of endophthalmitis but also are cosmetically unattractive. The dose of agents should be determined on clinical grounds and varied according to the risk of postoperative bleb failure.

Unfortunately, dysmorphic blebs will occur in spite of the surgeon’s best efforts. In considering the management of these blebs, we will deal separately with elevated and diffuse blebs. These are not mutually exclusive entities and management techniques can be combined where appropriate to achieve the desired outcome.

3.MANAGEMENT

3.1.The Elevated Bleb

In assessing the elevated bleb, the distinction should be drawn between Tenon’s cysts (see Chapter 6) that arise in the early postoperative (within 2 3 months following surgery) and the cystic blebs that arise after this period. When examining the lid margin, misdirected lashes or upper lid entropion may require immediate correction if the risk of bleb trauma from misdirected lashes is high. The simplest procedure is to epilate the lashes but it is important that the lashes are removed completely. Broken lashes can represent a greater risk for bleb damage as they are stiffer and can perforate thin conjunctiva. Cryotherapy to individual lash roots may be required to ensure complete removal of the lash.

Attention should also be given to the stability of the tear film. If dellen are present they indicate areas of tear film instability and local corneal dehydration. If untreated, they can result in epithelial breakdown and predispose to the development of bacterial keratitis. In most cases, dellen respond well to topical lubricants applied regularly at first but then as required. Gentle massage through the lids over the dellen can be a useful way of improving corneal hydration following the instillation of topical lubricants.

The other feature of elevated blebs is that because they are often thin walled, they are prone to develop small leaks which can be hard to detect. It is important that these leaks are excluded in any assessment of the bleb as they increase the risk of bleb infection and hinder the reliable control of IOP. If a leak is identified, antibiotic drops should be started to minimize the risk of endophthalmitis as the patient is prepared for surgical revision of the bleb (see Chapter 23).

The simplest approach to the elevated bleb is to re-contour the anterior edge of the bleb. This can be done quite simply under topical anesthetic by applying light diathermy to the bleb surface. It is critical that the bleb does not become adherent to the diathermy as the surface of the bleb will be removed and major bleb revision will then be required.

The appeal of this approach is that it can be applied as required to remodel the bleb surface. In our experience, it is well tolerated by patients and can be repeated as required. Other methods that have been advocated to alter the bleb surface contour include laser treatment and cryotherapy.

If a leak has been identified, the simplest approach to sealing the bleb is subconjunctival injection of autologous blood (8). This is simple and safe for the patient and does not carry the risks associated with the use of commercially available fibrinogen. Fibrinogen can be prepared from the patient’s own serum but this is not a viable option in many clinics. The appeal of subconjunctival blood is that it can be given under topical anesthesia as an office procedure. In some cases, this can be combined with cautery, diathermy, cryotherapy, or laser (9) to the site of leakage. The principle disadvantage with this technique is that when used in isolation it can comprise bleb function and result is excessive scarring around the filtration site. In some cases, blood can enter the anterior chamber and result in marked increases in IOP (10). When using autologous blood, it is important to establish whether the patient is using anti-coagulation medications such as warfarin or aspirin. If these are used, clotting will be delayed and there is an increased risk that blood will enter the anterior chamber. In these cases, diathermy can be applied at the time of subconjunctival injection so that the delivered thermal energy restricts the blood to the injection site. It is advisable to warn the patient that they will have a large subconjunctival hematoma and to reassure them that this is an anticipated side effect of the treatment.

3.2.Remodeling the Bleb with Compression Sutures

The development of conjunctival compression sutures for the treatment of dysmorphic blebs (11 13) has been a very useful advance in the management of these blebs. Nylon (10-0) or Vicryl (9-0) can be positioned as mattress sutures to run over selected portions of the bleb to provide physical compression bleb. Mattress sutures are inserted, under topical anesthesia, using a cutting edge needle, first at the limbus to run posteriorly to be anchored in conjunctiva Tenon’s two-thirds of the way back from the corneal limbus to the globe equator. Insertion of the anterior (limbal) suture is usually straightforward. The key to successful placement of the posterior suture is that they are inserted into Tenon’s tissue and not just the conjunctiva. If suturing at this depth does not provide a firm anchor point, the suture can be secured by taking a bite that includes the superficial layers of the sclera. As the eye retains full mobility, the patient is asked to look in the required direction to obtain adequate exposure of the posterior conjunctival areas. The anchor points for the sutures can be adjusted to suite variations in bleb morphology and sutures can be removed and reinserted as the configuration of the bleb responds to treatment. The width of the mattress suture will influence the degree of tension that can be applied to compress the bleb; the broader the bite used to secure the mattress suture in the corneal limbus and conjunctiva, the greater the tension that can be applied. Sutures can be used singly to demarcate one side of the bleb (Fig. 24.6) or two sutures (Fig. 24.7) can be used to demarcate both sides of the bleb. Sutures can also be used to demarcate areas of the bleb that require excision to reform the ocular contour at the limbus (Fig. 24.8). In these cases both ends of the suture are anchored at the limbus.

Compression sutures can be used effectively in combination with the subconjunctival injection of autologous blood (3,14). They are inserted prior to the injection and will limit the distribution of injected blood and can be used to prevent the passage of blood into the anterior chamber (Figs. 24.6 and 24.7). Blood is used because it increases the efficacy of compression and ensures continued apposition of layer induced by compression.

Figure 24.8 A suture has been inserted to compress the leading edge of a cystic bleb. The suture is anchored in the limbus either side of the bleb and runs parallel to the limbus. After several weeks, a scar line formed under the compression suture to seal off the part of the bleb overlying the limbus. This part of the bleb was then reduced by gentle cautery applied to the bleb surface to achieve a sat isfactory bleb contour.

filtration site can be mobilized and the anterior edge anchored to the limbus using 10-0 nylon mattress sutures. They have the advantage that they can apply sufficient traction to the conjunctiva without the development of small button holes at the site of insertion. If insufficient conjunctiva is available adjacent to the bleb, donor conjunctiva (15) can be obtained from the ipsilateral or contralateral eye to cover the filtration site.

3.3.The Diffuse Bleb

The treatment of these blebs can be difficult. Conventional management has included cryotherapy to demarcate the region of drainage or the insertion of conjunctival sutures to anchor the conjunctiva to the underlying sclera.

Compression sutures have been a significant advance in the management of these blebs. We almost always use the compression sutures in combination with autologous blood and usually plan to fill the entire drainage distribution of the bleb. In this case, the compression sutures provide a very effect barrier to prevent the passage of blood into the anterior chamber (Fig. 24.7). Blood injections can be repeated, as required, to facilitate adherence of the bleb to the underlying Tenons. The configuration of the compression sutures can also be adjusted during the course of clinical management to demarcate further subconjunctival blood injections as required or to adjust the degree of aqueous drainage. In cases of ocular hypotony compression sutures can be applied in a cruciate pattern so that they rest on the scleral flap and increase the resistance to the outflow of aqueous.

In cases where these measures are not successful, revision of the sclerostomy may be required. If the scleral flap is deficient, a scleral patch graft can be used; these can most easily be obtained as a partial thickness graft from the ipsilateral eye at a site diametrically opposite the filtration site.

4.CONCLUSION

There are many procedures for the management of dysmorphic and over filtering blebs. Ideally, surgery should be planned to minimize the risk for the development of the

dysmorphic bleb. Careful assessment is required to plan the strategy for bleb revision. Treatments should be given in a step-like fashion rather than as a single major bleb revision. In the majority of cases compression sutures, when used in combination with subconjunctival blood injection, can be used to remodel the majority of blebs and reduce the need for major bleb revision surgery.

REFERENCES

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12.Palmberg P. Late complications after glaucoma filtering surgery. In: Leader B, Calckwood J, eds. Proceedings of the 45th Annual Symposium of the New Orleans Academy of Ophthal mology. The Hague: Kugler Publications, 1996.

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extent, choroidal effusion size, and clinical course. Assessment is dynamic: it is the clinical course over time, which guides the therapy. Each case needs to be assessed on its own merits.

1.Assessment of the AC: Is the AC shallow or flat? Observers mean different things when they describe the AC as “flat.” We use this term to describe cases of lenticulo-corneal touch with “shallow” applied to all other situations. Documentation is important as shallow chambers, that is, those whose depth is shallower than normal or shallower than the other eye, usually spontaneously resolve with conservative measures whereas flat chambers with lenticulocorneal touch need urgent surgical intervention (2,6). It is important to document carefully the amount of irido-corneal touch in millimeters from the limbus. Spaeth (6) classifies flat AC from 1 to 3: grade 1 is peripheral iridocorneal touch, grade 2 is central irido-corneal touch, and grade 3 is lenticulocorneal touch. A classification of AC depth from 1 to 4 also exists (2).

An attempt may be made to perform gonioscopy to exclude a cyclodialysis cleft. Gonioscopy is difficult to perform with a shallow AC (especially if the eye is hypotonous) and is not productive if the AC is flat.

2.Always assess and document the state of the cornea (with or without corneal edema/folds in Descemet’s membrane).

3.Assessment of the bleb: Examine the bleb for extent. What is its size? Is there evidence of bleb function? Is there a wound leak? Use 2% fluorescein to look for a wound leak. Careful assessment of the bleb is usually the key to successful management of the case. If a wound leak is discovered, repair will resolve the situation. Most flat chambers, however, are due to over filtration associated with a large bleb. This scenario usually resolves in 1 3 weeks with conservative treatment consisting of mydriatics and limited steroid use (Dr. Morgan’s chapter on management of over filtering blebs).

4.IOP assessment: In cases with shallow or flat chambers due to leakage or over filtration, IOP should always be low. Choroidal effusions can be associated with IOP levels from 0 to 5 mm Hg as fluid fills the posterior segment and partially reinflates the eye. If IOP is measured in the high single digits, always reconsider your diagnosis and think of aqueous misdirection glaucoma or a supra-choroidal arterial hemorrhage. Aqueous misdirection glaucoma is not associated with clinically visible effusions whereas choroidal hemorrhage is usually associated with pain, large choroidal masses, and very high IOP. Pupil block may be associated with any level of IOP and also needs to be excluded.

5.Choroidal effusion assessment: Assess choroidal effusions for size and extent; are they “kissing” or not “kissing”? Kissing choroidals are an indication for surgical drainage. Assess the retina: exclude a serous retinal detachment. Choroidals are dark raised swellings unlike retinal detachments which are much paler. Ultrasound can determine the nature and extent of the supra-choroidal fluid. Effusions are typically dome shaped on B-scan, with a highly reflective anterior border and little internal reflectivity on A-scan. Ultrasound biomicroscopy (UBM) can yield further information, particularly about the presence of cyclodialysis clefts.

6.Assess degree of intraocular inflammation: Assess the level of anterior uveitis and the extent to which it is contributing to the hypotony and choroidal effusions.

4.MANAGEMENT

4.1.Intraoperative Techniques to Prevent Occurrence

Prevention is better than cure; anticipation and recognition of predisposing conditions is important. Meticulous technique with each step of the trabeculectomy is crucial. Controlled ocular decompression attempting to avoid intraoperative hypotony is important. With extremely high preoperative IOP, consider lowering the IOP before surgery using a systemic agent: slowly injected intravenous acetazolamide (250 500 mg) or intravenous mannitol (0.5 2 g/kg over 45 min). On the operating table, reduce IOP gradually by entering the eye first via a paracentesis and allow aqueous to exit slowly. Consider an AC maintainer to avoid intraoperative hypotony in extremely high-risk cases.

Intraoperative use of a viscoelastic does not prevent flat AC. A small, randomized trial comparing leaving or not leaving sodium hyaluronate in the AC showed an equal prevalence of hypotony in the two groups (7): the two cases of flat AC reported were in the viscoelastic group at postoperative days 4 and 7. If the AC tends to shallow at the end of surgery, we prefer to add additional scleral trapdoor sutures, and to consider cycloplegics “on the table”.

To reduce the chance of postoperative hypotony, some surgeons favor tight scleral flap closure to ensure AC stability with later laser suture lysis or releasable suture removal. We advise surgeons to check the tension on scleral flap sutures intraoperatively so as to attain the desired IOP postoperatively. This is the difficult art of trabeculectomy surgery. Inflate the AC with balanced salt solution (BSS) and observe the rate of aqueous egress under the scleral flap: rapid free flow of aqueous means the sutures are too loose; a tiny flow or flow occurring with minimal pressure on the globe is probably optimal; and if flow only occurs with pressure to the posterior lip of the flap, the flap is probably sutured too tightly.

Think carefully before using anti-metabolites, especially MMC. Even if its use is planned, reassess this need intraoperatively. Avoid MMC if the conjunctiva is torn or very thin, especially with minimal Tenon’s capsule. Concentrations used vary from 0.2 to 0.5 mg/mL for 1 5 min; consider using a lower concentration for a shorter duration. Carefully protect the edges of the conjunctiva during the application and wash away excess MMC at the end of the application. If using a fornix-based flap, close with wing sutures and consider a continuous limbal suture (8/0 vicryl). Close limbal based flaps in two separate layers especially if MMC is used. Pay meticulous attention to wound closure and check the wound at the end of the procedure with 2% fluorescein for water tightness. Treat inflammation vigorously after the surgery.

All filtering surgery should include an adequate paracentesis. Draw a diagram of your surgery, clearly indicating the site and direction of the paracentesis, to facilitate any postoperative accessibility.

4.2.Address the Specific Cause

To treat a flat AC effectively, it is crucial to ascertain its cause (see Fig. 25.1).

4.2.1.Wound Leaks and Over Filtration

Determine if there is a wound leak or an over filtering bleb and treat them (see chapter on leaking blebs and over filtration). Leaking wounds increase the risk of infection and bleb failure and reparative surgery is required when conservative measures fail. Conservative measures may include short-term aqueous suppressants, reducing steroids, and a bandage