Ординатура / Офтальмология / Английские материалы / Step by Step Minimally Invasive Glaucoma Surgery_Garg, Melamed, Bovet, Pajic, Carassa, Dada_2006

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sharper than a diamond blade whereas diathermy uses large amounts of energy but cuts poorly and damages the wall of the incision path, as seen on histologic sections.11

THE IMPORTANCE OF CONJUNCTIVAL

LYMPHATICS IN GLAUCOMA SURGERY

Conjunctival lymphatics are generally ignored in discussions of ocular fluid dynamics.12 However, if we visualize the extremely well knit lymphatic network under the conjunctiva, we soon realize that it has a role in fluid drainage in normal and operated eyes. Normally, over 30 percent of the aqueous humor filters out of the eye through uveoscleral outflow. There is an additional leakage from the anterior chamber through the aqueous veins. All this interstitial fluid has a substantial chance of being trapped by the lymphatics and then drained away from the eye. Post-surgical drainage is nothing short of managing a flood of aqueous – the lymphatics act as flood drains.13

The lymphatics and the Pallisades of Vogt are frequently visible under slit-lamp microscope as transparent channels and columns running parallel to the limbus (Fig. 24.3).14 However, the most spectacular view is seen in some patients who have pigmentation around the limbus. The pigment outlines the finest lymphatic channels at the limbus as well as the Pallisades of Vogt, (Fig. 24.4).15

Once it is realized that the lymphatics have a role in the drainage of the aqueous, the surgeons will then begin to understand the importance of doing minimal dissection, minimal cautery and minimal use of mitomycin C. The greater the trauma and destruction to the lymphatics, the greater the chance of scar and Tenon’s cyst formation with subsequent decrease of aqueous flow from the subconjunctival space and back into the vascular tree.16

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GLAUCOMA SURGERY TECHNIQUES WITH THE FUGO BLADE®

Four different techniques of glaucoma surgery have been developed and practiced. They are as follows:

1.Transciliary filtration (TCF).

2.Transconjunctival transciliary filtration (TC-TCF).

3.Microtrack filtration (MTF).

4.Non-perforating filtration (NPF).

Transciliary Filtration (Singh Filtration)17

The technique of surgery is as follows:

1.The conjunctiva is detached from the limbus for about 6-7 mm and it is retracted away from the limbus.

2.The Tenon’s capsule from the exposed sclera is excised with scissors.

3.The bleeding spots on the sclera are closed with the lowest energy of the Fugo Blade. A 600 microns tip is used for this purpose.

4.A scleral ablation point behind the surgical limbus is chosen for TCF. There is a variation dependent upon ocular type from high myopia to high hyperopia. The experienced TCF surgeon can easily identify the correct spot for scleral ablation, whereas the novice TCF surgeon can quickly and easily identify the location of the iris root employing anterior chamber transillumination. Instructional tapes on this are available from Medisurg, Ltd, USA (Tel 610-277-3937).18

5.The 600 microns tip is chosen to ablate the sclera at the chosen point. A scleral pit is formed (Fig. 24.5). The energy at medium settings is applied in small steps, until the ciliary body is visible. The edges of the pit are beveled especially at the proximal edge (Fig. 24.6).

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6.There is a choice of a 100 microns or a 300 microns tip for the next step, which is the next step of the creation of a track through the ciliary body into the posterior chamber (Fig. 24.7). The tip is directed behind the iris root, through the anterior part of the pars plicata. The tissue is touched a couple of times with the activated Fugo Blade tip until suddenly there is a rush of posterior chamber fluid along with small particles of ciliary body epithelium. The track formation is over in several seconds.

7.For demonstration purpose, air may be injected through the track with a 22 gauge cannula. The air appears in the anterior chamber from under the iris (Fig. 24.8). The posterior chamber may be irrigated in a similar fashion to wash out any pigment or blood. A drop of trypan blue placed on the track is washed away by outflow of aqueous.

8.Finally, the conjunctiva is lifted back to the limbus and sutured with one or more sutures (Fig. 24.9).19

TCF is done without a scleral flap or under a scleral

flap. Atwal has modified the technique such that he makes two tracksone transciliary and another one is made into the anterior chamber from under the base of the scleral flap. He terms the procedure the “Atwal Balanced Approach” or “ABA”.20 As of this writing, Dr Atwal has performed over 100 ABA procedures with a maximum follow-up time of slightly more than 4 months and with only 3 failed filters but with not a single collaped anterior chamber. Mitomycin is normally not used in the TCF operation. However, it can be judiciously used in high risk cases before making the scleral pit, or inside the pit before making the track through the ciliary body. Recall that this must only be performed with minimal exposure of the tissue to the mitomycin.

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Fig. 24.9: The conjunctiva has been sutured back to the limbus with 30 microns stainless steel suture

TCF is suitable for phakic eyes and pseudophakic eyes with an intact posterior capsule. Surgical errors are possible and manageable. A posteriorly directed perforating tip can disturb vitreous, which then may plug the TCF pore and therefore does not allow the aqueous to flow out. Repeating the ablation in an in and out movement of the activated Fugo Blade ablation probe into the area of vitreous causes plasma ablation of vitreous strands and thereby may open up ablation pits clogged with errant vitreous strands. If the surgeon wishes to reverse the TCF, the sclera may be closed at the site of the error with a suture. Then another site may be selected for a TCF track. The scleral pit may bleed excessively if the patient has a coagulation deficiency. This can occur with standard anticoagulation medication or with natural herbs or food such as high intake of fish, flax seed, ginsing balboa, vitamin E, etc. Make sure that there is no bleeding before proceeding to the next step of

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making a track through the ciliary body. In case there is any doubt, this site is abandoned and another close by site is chosen for restarting the procedure. Recall that the scleral pit takes seconds to create. Sometimes misdirection of the operating tip opens the track into the anterior chamber. Agitation of aqueous in the anterior chamber or formation of air bubbles in the anterior chamber is a diagnostic sign. In such a case, the anterior chamber is filled with air and another track is made somewhat posteriorly through the ciliary body into the posterior chamber. It becomes the Atwal procedure in reverse. It is imperative to make the posterior chamber ablation pit since this decompression of the posterior chamber all but eliminates flat anterior chambers postoperative, even with an eye pressure of 2-3 mm Hg.21

Postoperative management of the Fugo Blade procedures is much easier and more pleasant for both patient and physician than it is with trabeculectomy. There is practically never a flattening of the anterior chamber. Any bleeding into the anterior chamber is either from the angle or from the posterior chamber. It is uncommon. The blood is absorbed very slowly, since the greater fluid flow is through the posterior chamber. Choroidal detachment is comparable to that of trabeculectomy and is usually self absorbing.

Failure of the procedure is possible. In the first few days, the filtration track or the scleral pit may be closed by a blood clot. Another cause could be ‘posterior iris bombe’ which closes the internal opening. The track may be reopened after waiting for 2-3 days. The conjunctiva is detached from the limbus and then sutured back after the corrective procedure. Late failure can occur due to the formation of scar tissue or the formation of Tenon’s cyst. These are relatively easy to diagnose. The condition is

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treated by reopening the operation site and removing the scar tissue. The filtration track is usually found functional underneath the scar or the cyst. Mitomycin may be used with discretion and pinpoint application.

A primary success rate of over 80 percent is expected in cases of primary glaucoma. Furthermore, TCF is a filtering procedure that most anterior surgeons can perform rapidly and with a small amount of tissue manipulation. Importantly, postoperative chair time is minimized because flat anterior chambers are rarely seen, even with eye pressures of 2-3 mmHg.22 Cases of angle-closure glaucoma achieve chamber deepening with the procedure. The use of mitomycin increases the success rate in these cases, but it also seems to increase the rate of avascular bleb formation.

The procedure of TCF reduces surgery time, decreases tissue trauma and decreases the number and severity of early and late postoperative complications. Re-operation at the old site or an adjoining site is easy and without excessive trauma to tissues.23

The learning curve is low but there are techniques which must be mastered.24 There is significant surgeon variation in preference to surgical approach, e.g. ABA versus pure TCF. For example Dr Myron Wilson (Georgia, USA) and his associate Dr Johnny Gayton have performed over 30 pure TCF procedures (personal correspondence). They no longer employ anterior chamber transillumination and are now performing 3 TCF patients in a 15 minutes surgical block. They have had 2 failures in their group but note that re-ops are simple to perform. Most notably, they have stated that a large percentage of their TCF patients have the “most horrible pathology in our practice with no good option to treat” their glaucoma. Dr Herbert Kaufmann, Director of the LSU Eye Center, (USA) relayed a similar

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sentiment regarding his “worse eyes” glaucoma patients to one of the authors (RJF).

Transconjunctival Transciliary Filtration (Singh TC-TCF)25

In this technique, the posterior chamber is connected to the subconjunctival space without any dissection. This technique comes in handy in a number of situations like malignant glaucoma, painful neovascular glaucoma, pseudophakic glaucoma with iris bombe, and phakomorphic glaucoma preliminary to cataract surgery with or without IOL implantation. It is also helpful in such glaucomatous eyes that have extensive scarring, so that it is difficult to dissect close to the limbus. The operation is done under full local or a short general anesthesia. The steps are as follows:

1.The most important landmark is the point of reflection of the conjunctiva from the cornea. The second landmark is the posterior edge of the bluish looking surgical limbus (Fig. 24.10). The relationship between the first and the second landmarks should be clearly visualized. The scleral entry has to be about a mm. posterior to the surgical limbus. Keep that point in sight. It should be away from any big vessel on the sclera. Nonetheless, anterior chamber transillumination is simple to perform and gives the new TCF surgeon a definite location for a scleral ablation pit.

2.Gentian violet is applied on the conjunctiva over the limbus (Fig. 24.11). The conjunctiva is gripped with a forceps about 7-8 mm away from and parallel to the limbus. The conjunctiva is pulled down over the cornea. The attachment of the conjunctiva to the cornea becomes sharply visible as a blue line (Fig. 24.12). At