(1)
Aurelios Augenzentrum, Recklinghausen, Germany
(2)
Department of Ophthalmology, Faculty of Medicine, University of Szeged, Szeged, Hungary
Electronic supplementary material
The online version of this chapter (doi:10.1007/978-3-319-47226-3_4) contains supplementary material, which is available to authorized users.
First successful antiglaucomatous surgery was performed by the German ophthalmologist Albrecht von Graefe in 1852. The described technique did work only in acute angle closure glaucoma. In the following 100 years various surgical techniques addressed open angle glaucoma problematic. Since early 1970th trabeculectomy became the standard of care in open-angle glaucoma surgery. This widely used procedure involves a surgically formed pathway for aqueous humour between the anterior chamber and the subconjunctival space to lower intraocular pressure (IOP) in treatment of glaucoma. Main goal is the formation of a conjunctival filtering bleb. This is a relatively unphysiological approach and scleral as well as conjunctival scarring led to introduction of antimetabolites as adjunctive for filtering bleb depending glaucoma surgeries. Numerous intraoperative and postoperative complications have been cited [1–5]. These include hypotony, maculopathy, blebitis/endophthlamitis, hyphema, suprachoroidal hemorrhage or effusions, encapsulation of the bleb with resultant IOP elevation, loss of visual acuity, and increased risk for cataract formation. In addition, intensive postoperative care, including bleb massage, laser suturolysis, release of releasable sutures, needling, or 5-fluorouracil injections, may be needed to achieve primary success. Recently several authors reported relatively high failure rate of trabeculectomy after long term follow-up [1].
All this led surgeons to search for a more physiological and bleb independent surgical approach in IOP lowering glaucoma surgery. Surgical treatment of the natural aqueous outflow system, including Schlemm’s canal, to restore normal function and IOP control without penetration of the intraocular space has long been the interest in the study of open-angle glaucoma as an alternative to penetrating and bleb depending methods [6, 7]. In the late 1950s [8] and early 1960s [9], surgical procedures, often described as sinusotomy, were introduced to expose Schlemm’s canal and induce aqueous outflow without intraocular penetration. Further development of non-penetrating approaches included the use of a guarded scleral flap and creation of a descemetic window in the 1980s (deep sclerectomy) [10–12], dilatation of the surgical ostia of Schlemm’s canal with viscoelastic substance in the late 1990s (viscocanalostomy) [13], and the use of implants at the surgical site in the late 1990s and early 2000s [14–16]. These implants were either resorbable (i.e. SK Gel, AquaFlow) or non-resorbable (T-Flux). Most surgeons preferred to close the scleral flap loose to induce subconjunctival filtration in contrast to a watertight closure in viscocanalostomy, which could be named the first bleb independent non-penetrating glaucoma surgery. Although these non-penetrating surgical procedures for glaucoma effectively reduced IOP and lowered the incidence of postoperative complications compared with penetrating procedures such as trabeculectomy, comparative clinical studies indicates that IOP decreases more significantly with trabeculectomy, especially when used in conjunction with antimetabolites [17–23].
Cannulation of Schlemm’s canal with a silk suture was described in 1960 for partial trabeculotomy [24]. A modified technique using a 6 × 0 polypropylene suture was later used for 360° trabeculotomy for treatment of congenital glaucoma [25]. All previous non-penetrating glaucoma surgeries were able to reach two to three clock hours of Schlemm’s canal while a procedure treating the entire canal should be theoretically more effective. We reported a technique using the 6 × 0 polypropylene suture for catheterization of the entire Schlemm’s canal and while withdrawing the suture a 10 × 0 polypropylene suture is installed in the canal and finally knotted under tension [26]. Postoperative intraocular pressure after 1 year was 12.4 mmHg and medication was 0.3 IOP lowering drugs. This is a very difficult and time consuming technique with a relatively high risk of mispassage of the 6 × 0 polypropylene suture into the anterior chamber or suprachoroidal space. Recent advances in technology have allowed surgeons to use a flexible microcatheter to access the entire length of Schlemm’s canal more atraumatically. This technique is called canaloplasty (Fig. 4.1, Videos 4.1 and 4.2) and seems to be the logical evolution to viscocanalostomy [27, 28].
Fig. 4.1
UBM image after canaloplasty, Note: Schlemm’s canal clearly visible, gut distension of trabecular meshwork
This procedure is intended to overcome some of the problems of the previous procedures with deep sclerectomy.
The idea of implanting a fine tensioning suture into the Schlemm’s canal to enlarge the entire 360° of Schlemm’s canal [29, 30] should theoretically
widen the intertrabecular spaces,
preventing collapse of the canal, the surgical ostia and the descemetic window and herniation of the inner wall into the ostia of collector channels,
keep the entire Schlemm’s canal open
and
make collector channels away from the surgical site available for drainage.
First commercially available microcatheter for this technique was iTrack (Ellex, Australia, initially marketed from iScience Interventional, USA). This microcatheter has a 200 μm diameter shaft with an atraumatic distal tip approximately 250 μm in diameter. The device incorporates an optical fiber to provide an illuminated beacon tip to assist in surgical guidance. The illuminated tip is visible transsclerally during catheterization of Schlemm’s canal to identify the location of the distal tip of the microcatheter. The iTrack is connected to an external light source (iLumin, Ellex, Australia). The microcatheter has a lumen of about 70 μm with a proximal Luer lock connector through which an OVD (e.g. Healon GV or Healon 5) or dye (e.g. trypane blue, indocyanin green, fluorescein) could be delivered. The procedure is called viscocanaloplasty if OVD is injected to further stretch and enlarge the Schlemm’s canal. A dye could be used intraoperatively to control outflow system [31]. Later we developed a microcatheter (Glaucolight, DORC, The Netherlands) without lumen but reduced outer diameter for canaloplasty [32]. This device was directly connected to a sterile light source and less expensive. Currently Glaucolight is not commercially available. Recently a twisted polypropylene suture (Onalene for canaloplasty, Onatec, Germany) was marketed. The tip is atraumatic and catheterization seems to have a high success rate (personal experience). As it is not illuminated the advancement of the suture during catheterization cannot be controlled.
Surgical Technique (Videos 4.1 and 4.2)
1. Preparation of a superficial scleral flap.
The conjunctiva may be opened either at the fornix or at the limbus. A 5 × 5 mm rectangular or parabolic shaped scleral flap (scleral flap marqueur) is performed (Fig. 4.2) including one-third of the scleral thickness (about 300 μm, depending on the total scleral thickness in the particular case) (Fig. 4.1). To be able to reach the Descemet’s membrane later during the dissection of the deeper scleral flap, the superficial scleral flap has to be prepared 1–1.5 mm anteriorly into the perilimbal clear cornea (Fig. 4.3). The initial incision is made with a no.11 stainless steel blade (i.e. 15° slit knife for paracentesis) or a diamond knife. The flap dissection is made with a ruby blade or a bevel-up delicate crescent knife (i.e. 1 mm ultrasharp minidisc knife, Grieshaber Alcon, USA) (Fig. 4.4). Diathermy of episcleral vessels is prevented or reduced to a minimum. The episcleral vessels are part of the draining system and needed for successful canaloplasty. In case of excessive bleeding we use a delicate diathermy probe (25G endodiathermy probe) to perform focal diathermy.
Fig. 4.2
Superficial scleral flap, note no diathermy of episcleral vessels is performed
Fig. 4.3
Preparation of the superficial scleral flap with a mini crescent knife
Fig. 4.4
Dissecting the superficial scleral flap into the clear cornea
2. Preparation of a deep scleral flap.
Next deep sclerokeratectomy is performed by making a slightly smaller second flap then the superficial one, leaving a step of sclera at the sides allowing for a tighter closure of the superficial flap in case of an intraoperative perforation of the trabeculo-Descemet’s-membrane or intended watertight closure for viscocanalostomy/canaloplasty. Then the deep scleral flap is dissected towards the cornea using ruby knife or delicate crescent stainless steel knife (Fig. 4.5). This dissection has to be made down to a depth very close to the choroids/ciliary body and carefully carried anteriorly keeping the level of dissection as constant as possible. In case of opening of the suprachoroidal space dissection is continued just a few scleral fibers above. The change of the direction of the scleral fibers to a limbusparallel bundle indicates the scleral spur (Fig. 4.6). Just behind this the Schlemm’s canal is opened and unroofed. Care is taken to dissect the ostia of Schlemm’s canal clearly, because it is believed that this reduces the risk of collapse and scarring of these surgical ostia. Also entering the Schlemm’s canal with the microcatheter or a cannula is easier if the ostia can be identified clearly.
Fig. 4.5
Preparation of the deeper scleral flap using a mini crescent knife, note the smaller size of the deeper scleral flap
Fig. 4.6
Opening of the Schlemm’s canal, note the colour difference in the scleral bed indicating the right depth of preparation
3. Reduction of IOP.
A paracentesis/side port incision, which should be performed latest now is used to reduce intraocular pressure to very low level. This manoeuvre reduces the risk of perforation of the trabeculo-Descemet’s-membrane. Also it is necessary to control later IOP or inject air in the anterior chamber.
4. Creating a trabeculo-descemetic window
The dissection is then carried forward to expose a small segment of the Descemet’s membrane, creating a trabeculo-descemetic window of about 1–1.5 mm (Fig. 4.7). The corneal stroma can be blunt separated from the Descemet’s membrane i.e. with a sponge while the edges of the deep scleral flap are cut towards the cornea with the knife. In some cases the adhesion of Descemet’s membrane to the stroma is tighter. In these cases a blunt spatula or the mini crescent knife could be used with sweeping like limbusparallel motion to release these adhesions. This part of the surgery is quite challenging because there is a high risk of perforation of the anterior chamber. The deep sclerocorneal flap is then removed by cutting in the clear corneal part with a delicate small and very sharp scissor (i.e. Vannas or Galand scissor) (Fig. 4.8).
Fig. 4.7
Enlarging the descemetic window for optimal exposure of the trabeculo-Descemetic membrane, note the percolation of aqueous humour without perforation of the membrane, iris is visible through the intact membrane
Fig. 4.8
Deep sclerectomy – dissection of the deeper scleral flap with Vannas scissors
5. Insertion of the microcatheter
Now the ostia of Schlemm’s canal are gently enlarged by injecting a high viscosity OVD with the help of a special 31G cannula (Fig. 4.9). This will also help to reduce reflux bleeding into the surgical field. As the IOP starts to drop this occurs frequently at this stage of surgery. A specially designed forceps (Glaucolight forceps, DORC, The Netherlands) or a tying forceps is used to manipulate the microcatheter and place the tip into the surgically created ostia of Schlemm’s canal (Fig. 4.10). The microcatheter is advanced 12 clock h within the canal while the surgeon observes the location of the beacon tip through the sclera (Figs. 4.11, 4.12 and 4.13). After the catheterization of the entire canal length with the microcatheter and with the distal tip exposed at the surgical site, a 10 × 0 polypropylene suture is tied to the distal tip and the microcatheter withdrawn, pulling the suture into the canal (Fig. 4.14). To enhance the effect of canaloplasty an OVD can be injected while the iTrack microcatheter is retracted. If this additional injection of OVD into the entire canal is necessary, is unclear, while we could prove that the procedure did work without the use of iTrack catheter and circumferential injection of OVD 33.
Fig. 4.9
Viscocanalostomy with injection of OVD into the ostia of Schlemm’s canal with a special cannula
Fig. 4.10
Microcatheter before insertion into the Schlemm’s canal
Fig. 4.11
Red spot indicating the position of the microcatheter at 5 o’clock position in the Schlemm’s canal
Fig. 4.12
Intraoperative gonioscopic few with illuminated tip of the microcatheter (red dot) in the Schlemm’s canal, note the heavily pigmented trabecular meshwork in this eye
Fig. 4.13
After complete 360° cannulation of the Schlemm’s canal
Fig. 4.14
10 × 0 Prolene tensioning suture is fixed to the microcatheter
6. Insertion of a 10 × 0 polypropylene suture
After the microcatheter is removed from Schlemm’s canal the suture is cut from the microcatheter and then tied in a loop, encircling the inner wall of the canal using a slip knot or a locked four throw knot (Fig. 4.15). To reduce risk of rupture of descemetic membrane and to facilitate a more effective tensioning of the 10 × 0 polypropylene suture the IOP was previously lowered through a paracentesis.
Fig. 4.15
After withdrawing of the microcatheter the suture is cut off and knotted under tension to pull the inner wall of Schlemm’s canal and the descemetic window towards the anterior chamber to prevent failure of the surgery due to collapse of these structures
7. Check for perculation of aqueous
At this stage of the procedure, there should be perculation of aqueous through the remaining membrane evident. This can be checked also by applicating fluorescein to the surgical area (s.c. Rentsch-Seidel test). The amount of perculation is checked while drying the surgical area with a sponge. To increase the outflow facility, we peel partially the inner wall of the Schlemm’s canal, including the endothelium and the juxtacanalicular trabecular meshwork. A special designed forceps or an ordinary capsulorhexis forceps could be used. Occasional the inner wall of the Schlemm’s canal is fibrosed and an initial radial cut is necessary to be able to start the peeling. The next step of the surgery ophthalmic viscosurgical device (OVD) is injected in the surgical ostia of Schlemm’s canal.
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