Ординатура / Офтальмология / Английские материалы / The Art of Phacoemulsification_Mehta, Alpar_2001
.pdf
332 
THE ART OF PHACOEMULSIFICATION
should be considered for internal bleb revision at the time of cataract surgery. Alternatively, a patient with uncontrolled glaucoma in the presence of a bleb that has never demonstrated established function requires consideration be given to combining phacoemulsification with a second trabeculectomy and adjunctive mitomycin-C. Depending on the urgency of visual rehabilitation, proceeding with a second filtration procedure without concurrent cataract surgery might be most
appropriate.
Preoperative Considerations
While fortunately used less frequently, it is essential that miotics be discontinued preoperatively and if necessary, replaced temporarily with another topical agent or an oral carbonic anhydrase inhibitor. Currently, the indications for discontinuing the topical prostaglandin agents preoperatively are controversial.21 It is reasonable to consider initiating topical corticosteroid therapy a few days prior to surgery in an attempt to suppress any immediate postoperative inflammation. This can be combined with concurrent topical antibiotic therapy in the same period. We routinely recommend preoperative topical non-steroidal therapy in diabetic patients and those more prone to cystoid macular edema (CME).22, 23
Preoperative IOPs of less than 10 mm Hg in filtered eyes, are increasingly common as a result of the widespread use of antifibrotic agents with filtration surgery. Biometry and IOL power calculations are frequently less accurate in these marginally hypotonous eyes. A falsely short axial length measurement with the ultrasound probe can easily occur. The refractive error prior to the original trabeculectomy, as well as biometry of the fellow eye, should be evaluated in selecting an appropriate IOL power. In our experience, though not predictable, previously hypotonous eyes may have enough of an IOP increase following cataract surgery to result in a postoperative axial length increase and an apparent IOL power miscalculation. There is no simple IOL power algorithm in cases of hypotony. The operating surgeon is ultimately responsible for evaluating all biometric data to best select the most appropriate IOL power.
Preoperative evaluation of maximal pupillary dilation, as well as the presence or absence of pseudoexfoliation, will help in alerting the surgeon to a potentially more challenging and complicated procedure. Gonioscopic evaluation of the internal sclerostomy for location and patency is essential if internal revision of the bleb is planned.
We recommend avoiding external ocular compression devices like the Honan balloon immediately prior to surgery to avoid excessive hypotony or the possibility of bleb trauma. Moreover, the scrub technician must maintain a delicate approach to the preparation of the operative site.
Special Considerations during Cataract Surgery
Phacoemulsification in the presence of a preexisting filtering bleb is different in several respects from cataract surgery in an otherwise normal eye. First, every effort must to be made to avoid traumatizing the bleb, which nowadays can
PHACOEMULSIFICATION IN THE PREVIOUSLY FILTERED EYE 
333
Fig. 31.3: Kershner eyelid speculum provides excellent exposure
Fig. 31.4: Incision 90 degrees away from filtering bleb
be markedly thin and prone to rupture with something as simple as contact with a cellulose sponge. The lid speculum should be placed gently in the adjacent fornix after adequate irrigation, to reduce bleb trauma. A Kershner speculum (Rhein Medical) provides excellent exposure with minimal trauma under topical anesthesia (Fig. 31.3). Supplemental intracameral preservative-free lidocaine, allows complete pain free iris manipulation. The authors recommend a true clear corneal incision that totally avoids incising the conjunctiva. Placing the incision at least 90 degrees away from the bleb reduces the likelihood of direct trauma (Fig. 31.4). An incision that is directly anterior to a filtering bleb, increases corneal striae hampering visualization, delays wound healing, and increases the possibility of endothelial cell loss associated with a more central incision.24,25 Entering at the insertion of the conjunctiva or slightly posterior, can cause subconjunctival hemorrhage capable of extending into a preexisting diffuse bleb. Excessive Tenon’s hydration with ballooning of the conjunctiva may also occur and compromise visualization (Figs 31.5 to 7). A paracentesis for a second instrument must be far enough from the filtering bleb to avoid trauma during the surgery. The careful handling of sharp instruments, particularly diamond blades, cannot be overemphasized as an inadvertent superficial bleb laceration may create a problematic surgical procedure with an unstable anterior chamber, as well as disastrous long-term leakage in a patient with a thin avascular bleb. Similarly, scleral fixation devices should be avoided in these patients.
Deepening of the anterior chamber with a highly retentive viscoelastic agent, affords a well-controlled capsulorrhexis, and possibly temporary protection of the sclerostomy site from particulate lens matter during the emulsification. Care should be taken not to overinflate the anterior chamber forcing excessive viscoelastic into the bleb. The capsulorrhexis should be large enough (5-5.5 mm) to allow manipulation of lenticular fragments at the iris plane and avoid late capsular phimosis due to inadequate overall diameter (Figs 31.8 and 9). The requisite
334 
THE ART OF PHACOEMULSIFICATION
Fig. 31.5: Entering at the insertion of the conjunctiva
Fig. 31.7: Hydration and ballooning of the conjunctiva
Fig. 31.6: Incision just posterior to the insertion of the conjunctiva
Fig. 31.8: Capsular phymosis
liberation of anterior capsular debris with YAG laser photodisruption to treat any phimosis may potentially compromise bleb function and is preferably avoided.
Reduced pupillary diameter is generally the limiting factor in achieving an adequate anterior capsular opening. It is at this point that the surgeon must weigh the potential advantages of pupillary enlargement against the disadvantages of iris manipulation that is strongly associated with bleb failure. Pupillary enlargement is easily accomplished under viscoelastic with either iris hooks (Fig. 31.10), a Beehler pupil dilator (Moria instruments), or multiple small sphincterotomies. Gently
PHACOEMULSIFICATION IN THE PREVIOUSLY FILTERED EYE 
335
Fig. 31.9: Capsular fibrosis Fig. 31.10: Iris hooks in place
releasing any posterior synechiae and reinflating the chamber with a stiff viscoelastic, will often allow adequate capsulorrhexis and visualization. A fibrous circumferential band along the edge of the pupillary margin can occasionally be stripped gently with the capsulorrhexis forceps improving pupillary relaxation and dilation. The Graether pupil expander, or nylon iris retractors (Alcon Surgical) placed through 1 mm limbal paracentesis, are extremely helpful in not only stretching a miotic pupil, but in stabilizing the resulting lax and often floppy iris. This avoids repeated aspiration and trauma of the iris by the phacoemulsification tip that would otherwise occur with a simple stretching
maneuver. The pupillary margin need not be brought all the way to the limbal opening to be effective (Fig. 31.11). Unfortunately, even gentle pupillary stretching will result in microscopic sphincter tears with breakdown of the blood-aqueous barrier, and fibrin formation. Experience with phacoemulsification techniques more suited to small pupils, such as “phaco-chop”, can be a tremendous advantage to the surgeon and allow minimal iris mani-pulation.
Once the capsulorrhexis is complete, gently irrigating a portion of the viscoelastic from the anterior chamber will facilitate hydrodissection with less fluid pressure and avoid forcing excessive viscoelastic material into the sclerostomy and bleb.
336 
THE ART OF PHACOEMULSIFICATION
Fig. 31.12: Folded acrylic IOL prior to |
Fig. 31.13: IOL implantation |
implantation |
|
In cases of pseudoexfoliation or questionable zonular integrity, extra care should be taken to ensure the lens is completely hydrodissected and freely mobile within the capsular bag before beginning emulsification.
As emulsification starts, adequate but not excessive infusion bottle height should be maintained to avoid dramatically elevated intraocular infusion pressures capable of producing a bleb rupture. Complete cortical clean-up and posterior capsular polishing should be performed prior to re-inflating the capsule with viscoelastic, to insert the IOL. The authors currently prefer an acrylic foldable IOL through an incision size of approximately 3.2 to 3.4 mm (Figs 31.12 and 13). The acrylic IOL (AcrySofTM, Alcon), compared to silicone, tends to collect fewer giant cell deposits, produce minimal capsular phimosis, and less frequently require a capsulotomy.26-28 Meticulous removal of the viscoelastic material is essential. It is recommended that the I/A tip be placed behind the IOL, as well as anteriorly to aspirate all residual viscoelastic. Careful aspiration is performed at the internal sclerostomy to remove as much of the same material which may have gained access to the bleb. A less retentive or more cohesive viscoelastic such as sodium hyaluronate is preferable during insertion of the IOL, because of the ease of removing this material completely. The anterior chamber is reformed with balanced salt solution, evaluating the bleb for formation and flow. Intracameral carbachol (MiostatTM or CarbostatTM) can be infused at the end of the procedure to reduce the possibility of a substantial postoperative IOP spike.1An otherwise self-sealing clear corneal incision may not function as such in patients with a low preoperative IOP. When in doubt, the incision should be sutured to ensure wound stability and to allow the possibility of mild digital massage by the surgeon postoperatively.
PHACOEMULSIFICATION IN THE PREVIOUSLY FILTERED EYE |
|
337 |
|
||
|
|
|
Postoperative Considerations
One of the most concerning postoperative occurrences is a severe IOP spike. A pressure of greater than 25 mm Hg in the immediate postoperative period has been associated with a significant increase in bleb failure.3 In a patient with a very precarious optic nerve or threatened fixation, we advocate IOP evaluation within a few hours of the cataract surgery to allow prompt initiation of medical therapy if needed. In cases where the pressure spike is extreme, aqueous can
be immediately released through the paracentesis tract by simply depressing its 
posterior edge with a sterile instrument at the slit lamp. Frequent monitoring
of the patient’s pressure over the ensuing hours may be necessary.
Topical anesthesia for the cataract procedure, allows essentially uninterrupted frequent topical corticosteroid therapy to help reduce inflammation that can be associated with bleb compromise. The acute formation of fibrin resulting from iris manipulation may cause a dramatic IOP spike in the first few postoperative days. Obstruction of the internal sclerostomy by a fibrinoid clot or membrane, is the likely mechanism.29 These patients can be completely resistant to acute glaucoma medical management. We have experienced dramatic results with the use of intracameral tissue plasminogen activator (tPA) in such patients. The use of tPA to lyse fibrin clots in complicated glaucoma and cataract surgery has been well-described.12, 13 The prime concern in using this agent is the risk of an immediate and dramatic hyphema arising from the surgical site or an iris vessel cut during surgery. The occurrence of a hyphema with the use of tPA may be markedly reduced if the dose is kept between 6 and 12.5 µg.29 With a completely avascular clear corneal approach in the previously filtered eye and an appropriate tPA dose, hyphema appears much less likely based on our own experience in a limited number of cases.
Gonioscopically, the fibrin may not be readily visible at the internal sclerostomy. The dramatic effect and immediate action of intracameral tPA can nonetheless be remarkable. It is injected with a small cannula through a preexisting paracentesis site under slit-lamp visualization. Up to 12.5 µg can be placed in the anterior chamber with simultaneous release of aqueous. The resulting drop in IOP can be dramatic, occur within minutes, and is usually sustained. We recommend considering prompt use of this adjunct in cases of extreme and unresponsive early IOP spikes.
When IOP and postoperative inflammation are relatively stable beyond the first postoperative week, we recommend continuation of topical corticosteroids for at least four to six weeks with a slow taper. A delayed rise in the IOP beyond the first few weeks is generally indicative of late bleb failure. Although postoperative subconjunctival 5-FU injections may be reasonable in an attempt to avoid late failure, we are not aware of studies that support this. Sustained loss of IOP control requires the addition of glaucoma medications. As many as 10 percent of these eyes will require additional glaucoma surgery to regain pressure control.3 When indicated, the surgery should be performed promptly as the timing is not in any way restricted by the presence of a clear corneal cataract incision.
considered, before resumption of maximum tolerated medical therapy is required. Rather than waiting until all bleb function is lost, a less complex revision technique in conjunction with the cataract surgery can be employed to improve bleb function.
PHACOEMULSIFICATION IN THE PREVIOUSLY FILTERED EYE 
341
Fig. 31.22: External revision of the sclerostomy |
Fig. 31.23: Sutured scleral flap after revision |
Fig. 31.24: Tenon’s cysts before excision Fig. 31.25: Excised cysts
can be used to control aqueous flow (Figs 31.20 to 23). The conjunctiva is closed in a watertight fashion. Postoperative laser suture lysis may be used to modulate scleral outflow.30
A large limbal-based incision may be used to dissect superficial conjunctiva off a Tenon’s cyst and expose the vast majority of the underlying cyst wall. Before excising the cyst, mitomycin-C can be applied around the base and adjacent Tenon’s capsule and episclera. All visible aspects of the cyst wall are then excised. The more anterior scleral flap is evaluated and dissected as needed to establish adequate outflow (Figs 31.24 and 25).
An external approach to revise an encapsulated bleb or Tenon’s cyst has been described utilizing a small fornix incision. The technique utilizes a Kelly-Descemet punch to remove a portion of the cyst wall through this small incision.31 This approach does not readily allow the application of mitomycin-C.
The postoperative care and complications of filtering bleb revision surgery are similar to primary filtration surgery. Frequently, the early postoperative pressure