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Stab incision glaucoma surgery offers alternative to trabeculectomy
A single 2.8-mm conjunctival incision is used in the procedure, with no subconjunctival dissection.
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Trabeculectomy is the gold standard surgery for reducing IOP in patients with glaucoma. However, one of the disadvantages is failure secondary to subconjunctival fibrosis with the formation of the so-called “ring of steel.”
We describe a new guarded glaucoma filtration procedure that we have termed stab incision glaucoma surgery, or SIGS, which in our experience offered us various advantages compared with conventional trabeculectomy. This technique was conceived by Dr. Jacob.
Surgical technique
SIGS with MMC. A: Conjunctiva pushed forward. B: Keratome making a scleral tunnel entry. Keratome enters 1 mm into lamellar cornea but does not enter the anterior chamber. Note the blade is just seen through overlying sclera and conjunctiva. C: MMC 0.03% applied on a pledget into the scleral tunnel for 2 minutes. D: A thorough wash is given, and the anterior chamber is then entered.
Images: Agarwal A, Jacob S
A: Kelly’s Descemet’s punch is used to punch the posterior lip of the corneoscleral tunnel, which compromises the tunnel and causes it to leak. B: As the ostium is more posterior than usual, a peripheral iridectomy is performed. C: Side-port irrigation is done with balanced salt solution to check for adequacy of flow. Free flow of fluid should be seen. D: Conjunctiva is sutured, and bleb is elevated by balanced salt solution irrigation.
A: Six-month anterior segment optical coherence tomography showing the punched-out ostium (longitudinal scan). B: Horizontal scan showing ostium. Note in Figures A and B, the ostium is seen to be placed well away from the iris base, thus negating the need of a peripheral iridectomy. C: Subconjunctival cystic spaces seen in area well away from the tunnel, showing diffuse filtration through tunnel. Inset: Picture of eye undergoing anterior segment OCT. White arrow shows scanned area. Black arrow shows location of SIGS tunnel.
A 26-gauge needle is used to instill viscoelastic into the anterior chamber. The clock hour for SIGS is selected as is normally done for trabeculectomy. A superior or superonasal location or any other area with mobile conjunctiva is selected. The conjunctiva is slid forward and a stab incision made with a 2.8-mm keratome starting about 2 mm behind the limbus. The keratome is passed in a single movement through the conjunctiva and into lamellar sclera. A superficial lamellar scleral tunnel is dissected until the limbus. The ideal depth of the tunnel at this stage should be so that the blade is just seen through overlying sclera and conjunctiva. At the limbus, the keratome is angled slightly anteriorly to enter lamellar cornea. The corneal tunnel is similar to a short phaco incision. The point of the blade is introduced about 1 mm into clear cornea before turning the keratome horizontally and entering the anterior chamber. The keratome enters the anterior chamber horizontally without applying downward pressure. The blade is withdrawn, and if required, minimal viscoelastic is instilled into the eye through the stab entry. At all times during the creation of this sclerocorneal tunnel, the eye should be held firmly at the limbus with toothed forceps to enable good control over the position of the eye. As the conjunctiva is initially slid forward well toward the limbus before creating the tunnel, on removing the blade it slides back to its original position. The conjunctival cut is thus well separated from the scleral tunnel. Conjunctiva may also be pushed downward and sideways instead of straight downward, if the surgeon so prefers.
A 1-mm Kelly Descemet’s punch is then slid along the tunnel into the anterior chamber and used to punch the internal (posterior) lip of the corneal section. Care is taken to verify that the punch faces posteriorly before punching. Additional punches are taken, extending posteriorly until the limbus. Linear punches longitudinally are generally enough. Viscoelastic is gently irrigated out, and the tunnel is tested for leakage. This is done by irrigating balanced salt solution through the side port and looking for its leakage from the SIGS tunnel. A free flow of fluid should be obtained without having to apply excess irrigating force. Additional punches toward the limbus are taken in case of inadequate leak. Viscoelastic is finally removed with a Simcoe cannula introduced through the SIGS tunnel or through a side port. The 2.8-mm conjunctival cut is then sutured. Balanced salt solution is again irrigated through the side-port entry to elevate the bleb.
A peripheral iridectomy is not done routinely for cases with primary open-angle glaucoma and wide open angles. This is because the ostium is more anterior than with a trabeculectomy and is placed well away from the iris. It is created only for cases with primary or secondary angle-closure glaucoma, peripheral anterior synechiae or shallow anterior chamber or if the iris is seen peaking into the ostium on irrigating with balanced salt solution. It may also be required if the corneal part of the tunnel is short. The peripheral iridectomy may be done easily by using non-toothed forceps to pull out the base of the iris through the tunnel. Curved Vannas scissors are then used to cut the iris. It is easy to perform if the assistant holds the conjunctiva forward to improve visualization and access. Once the peripheral iridectomy is done, it is important to push the iris back into the anterior chamber to avoid incarceration within the tunnel.
Mitomycin C
SIGS can also be combined with mitomycin C. The keratome is stopped in the lamellar cornea just before entering the anterior chamber. MMC 0.03% is then applied into the tunnel with a small sponge. Because there is no subconjunctival dissection in SIGS, subconjunctival application of MMC is generally not required. After 2 minutes, a thorough rinse is given and the tunnel filled with viscoelastic to enable the keratome to easily slide back in. The anterior chamber is then entered through the corneal valve, and surgery continues as described previously.
Phaco with SIGS
We were also able to effectively combine SIGS with phaco. The location for SIGS is chosen such that it does not interfere with the creation of the main and side ports required for phacoemulsification. The SIGS stab incision is made and anterior chamber entered. Routine steps of phacoemulsification are then proceeded with. As the SIGS incision at this stage is a self-sealing tunnel, it does not leak, cause shallowing of the anterior chamber or interfere with phacoemulsification in any other way. After IOL implantation, with viscoelastic still in the eye, the Kelly Descemet’s punch is used to punch the inner lip of the corneal tunnel as described previously. Leakage is confirmed by irrigating balanced salt solution through the side port. After confirming an adequate leak, the conjunctiva is sutured and viscoelastic removed from the anterior chamber with an irrigation and aspiration probe. Good ballooning of the bleb shows an adequate filtration through the SIGS ostium.
Discussion
A posterior corneal lip is essential for performing SIGS because it is this lip that is punched and thereby the self-sealing nature of the tunnel compromised. Care should therefore be taken to avoid premature entry into the angle of the anterior chamber. If this occurs, it is simple to convert into conventional trabeculectomy by very slightly extending the conjunctival cut to either side. The conjunctiva is dissected off the scleral tunnel in a blunt manner, and the tunnel is cut at both sides. This converts the tunnel into a flap. The flap is dissected forward into the cornea, and a trabeculectomy is then performed as usual. The flap and conjunctiva are then sutured.
SIGS offers numerous advantages over conventional trabeculectomy. SIGS has only a single small 2.8-mm conjunctival incision well away from the scleral cut. There is almost no subconjunctival dissection, and hence the risk of scarring and failure is reduced. Hydrostatic dissection from the pressure of the fluid from side-port irrigation or from the I&A probe causes formation of the bleb. Conjunctival drainage channels are almost intact, and this is therefore more physiological. SIGS maximizes the amount of untouched conjunctiva so as to allow space for a repeat SIGS or other glaucoma surgery in the future if required. A controlled posteriorly directed flow is obtained. The scleral tunnel allows guarded filtration. There are fewer suture-related complications. In addition, it is a faster and easier technique. It is easy to convert to conventional trabeculectomy if required. SIGS is also economically viable to perform and does not need any expensive device or instrumentation, unlike many of the microinvasive glaucoma surgery procedures.
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- Amar Agarwal, MS, FRCS, FRCOphth, is director of Dr. Agarwal’s Eye Hospital and Eye Research Centre. Agarwal is the author of several books published by SLACK Incorporated, publisher of Ocular Surgery News, including Phaco Nightmares: Conquering Cataract Catastrophes, Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery and Presbyopia: A Surgical Textbook. He can be reached at 19 Cathedral Road, Chennai 600 086, India; email: dragarwal@vsnl.com; website: www.dragarwal.com.
Disclosure: No products or companies that would require financial disclosure are mentioned in this article.