Ординатура / Офтальмология / Английские материалы / Clinical Pathways in Glaucoma_Zimmerman, Kooner_2001

470 Surgical Therapy for Glaucoma

to combined cataract/glaucoma surgery. The scleral tunnel technique allows for the most uniform and reproducible scleral flap.

A cornerstone to the concept of this surgery is that the scleral flap will be made almost watertight with the intention of performing laser suture lysis postoperatively. This greatly reduces the biggest risk for complications in glaucoma surgery, namely postoperative hypotony. This concept has revolutionized glaucoma surgery in that good filtration can be obtained without many of the risks encountered with earlier techniques, such as full-thickness trabeculectomy, Elliot’s trephine, cyclodialysis, etc.

Be sure to prepare the patients beforehand that they will likely have laser suture lysis between 1 and 4 days following surgery. They should be informed that this is a routine part of this type of glaucoma surgery and that although it is an extra step, they are receiving the safest form of surgery.

What Is the Mode of Action of Trabeculectomy?

The goal of glaucoma filtration surgery is to produce a fistula from the anterior chamber through the sclera to allow a controlled amount of aqueous to egress into the subconjunctival space (thus lowering IOP). The aqueous is then reabsorbed into the bloodstream by subconjunctival venules. Transconjunctival evaporation also likely occurs.

What Are the Principles of the Trabeculectomy Procedure?

•Administer inferior and superior peribulbar block; apply intermittent digital pressure until the globe is soft.

•For sterilization, prep with a 50% Betadine solution. Also use it topically to irrigate the cul-de-sac. (Use 25% topically if the case is being done under topical anesthesia.)

•Use talc-free gloves to reduce the chance of Tenon’s cyst formation.37

•Insert a wire lid speculum.

•Pass an 8-0 Vicryl suture through the superior peripheral cornea about 3 mm from the limbus as a corneal traction suture. (Inferior corneal traction sutures also work well if tucked below the lid speculum.)

•For a fornix-based flap, perform a conjunctival peritomy. This is made about 8 to 10 mm in chord length.

•Take special care not to tear the conjunctiva. Use only conjunctival forceps (which has ridges but not teeth) so that conjunctival edges are not torn.

•At the beginning of the peritomy, a relaxing incision is made by initially entering the conjunctiva 4 mm posterior to the limbus to gain access into the sub-Tenon’s space and thereby allow for a sub-Tenon’s dissection, because Tenon’s ends before the conjunctiva at the limbus. This initial entry should be well away (8 mm) from the intended trabeculectomy site.

•After the initial entry, it is important to dissect sub-Tenon’s for the full extent of the conjunctival incision and as close to the limbus as possible. This will expose bare sclera.

•Do not perform aggressive undermining of the peritomy into the quadrants. Just open the conjunctiva enough to allow adequate exposure for

surgery. Further posterior dissection is counterproductive, as it only aggravates the inflammatory response.

•Eraser-tip wet-field cautery is used for bleeders and to lightly blanch the area of the sclera to be incised (sclera flap).

•Use a Beaver blade no. 6600 because this single blade can be used for both steps of the formation of the scleral flap.

•Begin the scleral incision 4 mm posterior to the limbus and parallel to it.

•Use the blade to make a three-quarter depth scleral incision. Stop when the deeper blue hue of the inner sclera is seen. Get a feel for the thickness of the sclera and try to achieve the correct depth within the second or third pass. Make the incision about 4 to 5 mm long.

•Turn the blade over so it is parallel to sclera and insert the rounded tip into the deepest part of the incision. Use a wiggling motion to advance the rounded tip within a single plane (parallel to the sclera surface) and into clear cornea. If too much resistance is encountered as the blade advances, then the established plane may be too shallow. This part of the incision is identical to the typical scleral tunnel cataract incision, which is why it is so well adapted to combined surgery, even though the initial incision is not quite as anterior as with typical cataract surgery.

•Advance the blade until it can be visualized about 2 mm beyond the limbus into clear cornea.

•Widen the scleral tunnel so that it is exactly uniform to the edge of its original scleral entrance incision, that is, 4 to 5 mm wide. If the tunnel is made wider than the incision, it will be difficult to get the sclera flap watertight.

•Use Vannas scissors to open both sides of the tunnel to the surgical limbus. Be sure the scissors blades are exactly perpendicular to the sclera that is being cut. Enter the tunnel flat with one blade of the scissors, and then turn the scissors so the blades are perpendicular to the surface of the sclera (one blade within the tunnel, one blade on top of the sclera) and slide the scissors sideways all of the way to the edge of the tunnel to get this incision as perpendicular and uniform as possible. Usually, it takes three or four snips to get to clear cornea on each side. Go up to but not beyond clear cornea or else leakage may occur here.

•Lift the flap and there should be a uniform direct view of the cornealscleral junction. At least 1 mm of clear cornea should be viewed anterior to this lamellar junction. If this is not seen, then use the Beaver blade again to establish that length.

•If using MMC, first close the scleral flap and apply 0.2 mg/mL for 2 minutes38 on top of the scleral flap. 5-FU in a concentration of 25 to 50 mg/mL for 5 minutes also works well and may be safer.39 Unlike MMC, 5-FU is not a strong alkylator and though toxic to cells of replication (fibroblasts), it has little effect on static cells (sclera). Comparatively speaking, 5-FU is less destructive to scleral and conjunctival tissue and therefore carries less of a chance for late-onset bleb leaks and associated infections. The instru-

ment wipe sponge or corneal light shield40 provides a more uniform uptake of MMC or 5-FU than does the Weck cell. Cut a 4- × 4-mm piece of this sponge and place it directly over the scleral flap after it has been soaked in the antimetabolite. Care must be taken to make sure that no edges of the conjunctiva touch the sponge. The sponge does not go under-

472 Surgical Therapy for Glaucoma

neath the scleral flap, but simply sits on top of it.41 After 2 minutes, use a Weck cell to dry the area completely, and then use copious amounts of balance salt solution (BSS) to dilute any remaining antimetabolite. It is helpful to lift the conjunctival edges up so that they are not in contact with the solution while irrigating.

•Use a microsharp blade to create a paracentesis site at the temporal limbus. If topical subconjuctival anesthesia is being used, then inject the nonpreserved intracameral lidocaine 1%.

•If the chamber is at all shallow, then apply a small amount of viscoelastic just at the 12 o’clock site to deepen the chamber just beneath the trabeculectomy. It is not necessary or desired to fill the whole chamber with viscoelastic in most cases.

•To establish the trabeculectomy site, use a microsharp knife (or 2.6-mm keratome if performing phacoemulsification) to enter the anterior chamber beneath the scleral flap. This is done in the same manner as in a paracentesis. The entrance of this incision should be at least 1 mm anterior to the corneal scleral juncture, that is, 1 mm into the cornea and 3 or 4 mm in length. Be sure it is near the center of the overlying scleral flap, and not near its edges.

•If the chamber shallows as this incision is made, then use viscoelastic to focally push the iris back down.

•Insert the Kelly or Holth scleral punch. It must be inserted with the blade open. Be sure it is completely within the eye. (It usually is a tight fit and one feels it “pop through” into the anterior chamber.) Then rotate the instrument so it is directly perpendicular to the scleral plane (rotate the handle upward).

•Once the instrument is perpendicular to the scleral surface, snip out the corneal-scleral junction and proceed snipping bits of tissue into the trabecular meshwork. With each snip inspect the tissue removed, and remove it from the guillotine. If the tissue is carefully inspected, the small pigmented lines of the trabecular meshwork can usually be seen once it is reached. Once the TM is removed, no further punching is needed. Usually, this requires two to three snips posteriorly. Keep the width of the punch excision to a single width. The inner block of corneal-sclera that is removed only needs to be one punch wide to work properly. Two to three punches posteriorly usually penetrate trabecular meshwork, and often into scleral spur.

•As you approach TM with the punch, be sure that the punch does not entrap a peripheral iris roll, iris root, or the anterior portion of the ciliary body. Cutting these will result in profuse bleeding.

•When done properly, heavy bleeding with the above procedure is rare. If it occurs, then Myra cautery or a retinal cautery (pointed tip) will likely be needed for control.

•Use a 0.12 forceps and Vannas scissors to create a small underlying iridotomy. When using the forceps to grasp the iris, it is important to grasp the iris more central than the tissue that presents at the trabeculectomy site to avoid pulling the iris root or cutting the anterior portion of ciliary body or iris arcade. That is, grab a point slightly peripheral to the mid-iris, where the peripheral one-third of the iris meets the central two-thirds.

•Once the iridotomy is made, reapproximate the scleral flap and use BSS on a 27-gauge cannula through the paracentesis site to flush the anterior chamber free of viscoelastic and to establish filtration.

•It is important to prevent the eye from becoming hypotonous (flat chamber) at any point in the case, as this will precipitate anterior displacement of the ciliary body. Use BSS or viscoelastic as needed.

•Next, secure each corner of the scleral flap back down using a 10-0 nylon suture. Cut the sutures on the knot, and try to bury the knot outside of the scleral flap.

•Check filtration by injecting BSS (on a 27-gauge cannula) through the paracentesis and watching the flow rate around the scleral flap. In white patients with nonscarred eyes, there should be almost no leakage at normal pressures. Instead, a white glistening reflex is seen in the scleral groove. If leakage occurs, continue using interrupted 10-0 to make the flap almost watertight. By injecting BSS, an IOP in the mid-teens should be established. In blacks or patients suspected of scarring, slightly more filtration can be allowed. Still the filtration should be a bare trickle, and an IOP of about 10 mm Hg should be maintained after injecting BSS.

•In addition to the corner sutures, often several additional sutures are required to get the scleral flap sufficiently leak-free at normal IOPs. Using BSS through the paracentesis, our goal is usually to establish filtration that allows for an IOP of about 10 to 15 mm Hg. Once this is established, it is a good idea to recheck after 1 or 2 minutes to be assured that the eye is holding that pressure. If so, the end point is reached, and the eye is ready for closure.

•Once the conjunctiva is reapproximated to its original position over the trabeculectomy site (but prior to suturing), it is mandatory to assess the amount of Tenon’s capsule over the trabeculectomy site. Remember that the sutures that close the scleral flap must be easily visible through the conjunctiva to allow for suture lysis postoperatively. It is therefore usually necessary to tease away and remove one or two layers of Tenon’s capsule beneath the conjunctiva to allow for this. Using a conjunctival forceps to pick up the anterior lip of the incision of conjunctiva, the underlying Tenon’s layers can be split away using the Vannas scissors in a blunt dissection method. This must be started at the area of the initial conjunctival relaxing incision where Tenon’s capsule and conjunctiva can be separated. By inserting the scissors with tips closed into this potential space, and then spreading with scissors, a plane can be established. Then the scissors can be used to remove this excess tissue above the scleral flap site. Extreme caution must be exercised to prevent buttonholing of the conjunctiva. Irrigation of BSS on a 27-gauge blunt cannula can be helpful to establish this potential tissue plane. Once Tenon’s capsule is removed and the translucent conjunctiva reapproximated, the 10-0 nylon should be easily visible through it. (Separate dissection of conjuctiva and Tenon’s capsule at the beginning of the case is also an alternative and sometimes is easier.)

•To close the conjunctiva reapproximate it to its original position and hold it in place with a 10-0 nylon (BV needle) at each corner of the original limbal incision. Be sure to include a bit of episcleral tissue so that the conjunctiva

474 Surgical Therapy for Glaucoma

does not retract, and it will be held fast to that spot. Additional interrupted or running 10-0 nylon (BV needle) is then used on any relaxation incisions that were created. With all interrupted sutures, it is best to cut on the knot.

•Now use the Beaver blade to rough up the epithelium of the clear cornea at the limbus overlying the trabeculectomy site so that the conjunctiva will better stick down at the site.

•To keep the conjunctiva from retracting at the limbal site of the trabeculectomy, an anterior circumferential suture is quite helpful, and is used in almost all cases. A 10-0 nylon suture on a spatula needle is passed into clear cornea just central to the limbus at the point where the conjunctiva should adhere. The needle track runs parallel to the limbus. The entrance of the needle is at one side of the trabeculectomy site in clear cornea, and the exit of the needle is at the other side of the trabeculectomy site in clear cornea. The needle passes three-quarter depth through the cornea. Next, impale the conjunctiva near its lip from the underside so that the needle exits from the surface of the conjunctiva. The nylon then passes over the surface of the conjunctiva, and the needle is then passed from the outside surface of the conjunctiva near its lip (at the other end of the trabeculectomy site) to its undersurface and pulled out from underneath the free edge of the conjunctiva. Then this loop is tied and the knot is rotated slightly so that it is underneath the conjunctival lip. When the knot is properly tied, the conjunctiva will be pulled down over the limbus, and the lip of conjunctiva will cover the knot. Use BSS through the paracentesis site to see if a bleb is created. In patients with scarring who need some filtration, a bleb should be created. In patients who are thought to leak easily, the trabeculectomy is closed watertight and a bleb will probably not be noticed. If there are any potential gaps in the conjunctiva, they should be closed with interrupted 10-0 nylon. This is especially important if MMC is used. If no filtration occurs, then be sure to use the paracentesis site to reduce IOP to the low-teens range. Suture lysis will be required in 24 hours. If IOP is not sustained to at least 10 mm Hg, then additional scleral sutures will likely need to be applied, which will require taking the conjunctiva back down. The rare exception to this is if one expects a high degree of outflow dysfunction in the trabecular meshwork, and a high degree of aqueous production, which will support additional filtration. Sometimes lower pressures will be tolerated if the anterior chamber is very deep and the iris is stiff. In most patients, however, it is best to take the conjunctiva back down and “tighten up” the filtration at the scleral flap if the eye does not hold at least 10 to 15 mm Hg.

How Are Combined Cataract and Trabeculectomy

Procedures Planned?

When combining this procedure with cataract surgery, there are two major differences:

1.Make the initial scleral flap incision slightly more anterior than usual to make it easier to perform phacoemulsification. That is, instead of beginning a flap 4 mm posterior to limbus, create the incision 2 to 3 mm posterior to the limbus.

2.After the flap is made and it is time to enter the eye, use a keratome (usually 2.6 mm wide) to enter the anterior chamber underneath the flap. Enter in the same way one would normally during a scleral tunnel type cataract surgery. Usually, the entrance for cataract surgery is slightly more anterior (further into clear cornea) than it is with trabeculectomy. This prevents the iris root from coming up through the incision site during phacoemulsification and aspiration.

After the cataract is removed, viscoelastic is used to fill the capsular bag as well as the anterior chamber. The incision is enlarged to about 3.5 mm and a foldable implant (Acrysoft of other nonsilicone material) is inserted.

Before removing viscoelastic from the eye, finish the trabeculectomy. It may be necessary to use a microsharp blade to make another entrance into the anterior chamber beneath the flap, which is more posterior than the existing cataract entrance, to make it easier to use the scleral punch. When more experience is gained, a single entrance into the anterior chamber (i.e., halfway between the normal cataract entrance and the normal trabeculectomy entrance) can usually be used instead. After the iridotomy and before suturing the flap, use the irrigation/aspiration mode to remove the viscoelastic. Because the temporal clear cornea approach is so much easier for cataract surgery, many surgeons are performing each procedure separately.

What Is the Postoperative Care for Patients After

Filtration Surgery?

•Apply cycloplegics.

•Apply topical steroid/antibiotic ointment

•Avoid subconjunctival injections, especially when MMC was used. Leaks can develop through needle tracks.

•Apply topical beta-blocker if not contraindicated.

•Give Diamox 500 mg sequel to take with supper if not contraindicated.

•Remember a pressure spike is possible with this procedure, especially if no filtration is present initially.

•See the patient 24 hours later and consider suture lysis. Make note of which suture was required to stop leakage, plan to laser that suture first.

•Use Pred Forte 1% q.i.d. and Ocuflox or Ciloxin q.i.d. as needed. This is continued for at least 1 week, at which time the antibiotic is stopped and Pred Forte is continued q.i.d. another week, then tapered off by decreasing it to three times daily for 1 week, then twice daily for 1 week, then once a day for 1 week. If conjunctival inflammation is still present after tapering Pred Forte, then start fluorometholone (FML) 0.1% q.i.d. for one week and then begin tapering again. Any conjunctival sutures causing irritation should be removed at 1 week.

•If combined cataract surgery is done, Pred Forte 1% may be used more aggressively, that is, every hour for the first day, every 2 hours for 48 hours, and then four times a day for 2 weeks, and then taper as above.

476 Surgical Therapy for Glaucoma

How Is Suture Lysis Performed?

•Use a Hoskins lens to magnify the suture and compress the conjunctiva.

•Use the argon laser with a spot size of 100 m, power of approximately 200 mW, and time of approximately 0.1 seconds.

•Once a suture is cut, see if the bleb increases and IOP drops to the desired level. If minimal effect is achieved, then continue cutting other sutures one by one.

•Recheck patient again in 24 hours to see if additional sutures will need to be cut.

•Usually suturelysis is ineffective after 2 to 4 days. One of the reasons to use Pred Forte 1% every 2 hours is to extend the time that suture lysis may be effective, that is, usually only up to 48 hours, but with aggressive steroids, possibly up to 4 days or more in some patients.

What Are the Complications of Filtration Surgery?

Some degree of cataract formation is very common.30 Some other possible complications are listed in Table 19–4. The most common complications are related to the IOP being either too low or too high postoperatively.

Table 19–4. Complications of Filtering Surgeries.

Hypotony

Choroidal effusions Choroidal hemorrhage Hypotensive maculopathy Retinal vein occlusion Retinal detachment

Peripheral anterior synechiae/angle closure Optic nerve damage (snuff syndrome)

Pressure spike documented

Transient/occult pressure spike suspected (IOP back to normal on postop visit) Aqueous misdirection/malignant glaucoma

Damage from retrobulbar or peribulbar block Needle penetration

Increased intraconal or orbital pressure from hemorrhage or excess volume Dislodged embolus into posterior ciliary artery or central retinal artery

Infection Blebitis

Endophthalmitis

Anterior segment and corneal problems Cataract formation

Foreign-body sensation Dellen formation Astigmatism

Tearing Phthisis bulbi