Combined management of cataract & glaucoma
Everything you ever wanted to know about the management of co-existing cataract and glaucoma (part 2)
A: Stab-Incision Glaucoma Surgery (SIGS) – A Kelly’s Descemet’s punch is being used to create the SIGS ostium by punching the lower lip of the tunnel; B: Postoperative slit lamp view in SIGS; C: An Ex-Press shunt is seen post insertion; D: Postoperative slit lamp view with posterior chamber tube placement of an Ahmed Glaucoma Valve combined with phacoemulsification
In the second article of this multi-part series on combined management of cataract and glaucoma, we discuss three surgeries. In all three, parts of glaucoma surgery are first performed with a formed globe followed by phacoemulsification before creation of an ostium to allow safe cataract extraction under stable anterior chamber conditions. Finally, the remaining part of glaucoma surgery is completed.
SIGS (Stab-Incision Glaucoma Surgery):
SIGS is a surgical procedure described by the author aimed at minimising conjunctival dissection and obtaining posteriorly directed flow. In the author’s experience, it works well in primary and secondary open-angle glaucomas with adequate virgin conjunctiva. Either 0.2ml of 0.02% Mitomycin-C (MMC) is injected subconjunctivally 20 minutes prior to surgery or an intraoperative application may be done.
The speculum is loosened and conjunctiva pushed forwards with non-toothed forceps held flat against the globe to avoid conjunctival and scleral cuts from overlapping. A 2.8mm bevel-up keratome is used to initiate the biplanar SIGS tunnel. The ideal short and shallow tunnel incision starts 1.5mm behind the limbus, avoiding major blood vessels and at 1/3 thickness sclera. This is verified by just seeing the metal keratome through the overlying sclera.
The angulation of blade is matched to the scleral curvature to get a uniformly thick tunnel. At the limbus, angulation is increased to match steeper corneal curvature. About 0.5-1mm into the clear cornea, a horizontal entry up to the maximum width of the keratome is made into the anterior chamber (AC) parallel to the iris, avoiding posterior pressure on the tunnel.
Taking care not to hit the anterior capsule or the iris, the blade is then quickly withdrawn straight backwards avoiding sideways slicing movements to prevent damage to the side walls of the tunnel. Main and side ports are created as usual on either side of the SIGS tunnel and phaco is proceeded with. Cataract extraction can be performed with ease and the AC remains stable as the SIGS ostium has not yet been created.
After IOL implantation, the SIGS tunnel is intentionally compromised by using a 1mm Kelly’s Descemet’s punch to punch the posterior wall of the tunnel. The posterior wall is punched vertically backwards up to the limbus until it can be just seen on lifting up the conjunctiva and the anterior wall of tunnel. The AC is then shallowed so that the iris moves forward.
With the assistant retracting conjunctiva, a non-toothed forceps is used to pull the base of the iris out through the tunnel and a peripheral iridectomy is created using curved Vannas scissors held horizontally. The iris is then pulled back into the AC and viscoelastic washed out. Balanced salt solution (BSS) injected through the side port confirms adequacy of leakage through the SIGS tunnel if free flow of fluid is seen without shallowing of the AC.
If the AC deepens and becomes hard, shallow graded nibbling of the posterior lip is further done until such flow is obtained. The conjunctiva is then closed with continuous 10-0 nylon suture.
Residual viscoelastic is removed with an I/A probe. Inflation of the bleb during I/A together with a soft, stable and well-formed AC are good signs. Sutures may be applied on phaco main and side ports if required. As in trabeculectomy, releasable sutures may be applied if desired.
Advantages of SIGS include simplicity and effectiveness as compared to conventional trabeculectomy as well as cost-effectiveness and greater efficacy compared to many microinvasive glaucoma surgeries. The biplanar tunnel allows posteriorly directed flow and prevents formation of overhanging bleb. It also provides a diffuse area of leakage. SIGS also minimises conjunctival dissection with more virgin conjunctiva available for any future procedures.
This is a 3mm-long non-valved stainless steel, MRI-compatible device with a 50-micron lumen, a spur-like extension that prevents extrusion and a back plate to prevent erosion. It has a lower risk of hypotony as compared to trabeculectomy. A fornix-based conjunctival flap is created. A half-thickness scleral flap of 3x4mm is dissected to ensure adequate coverage around the Ex-Press shunt and to get adequate resistance with sutures to prevent over-filtration. The flap is dissected slightly forwards into the clear cornea to avoid compression on the shunt. If indicated, MMC is then applied as in trabeculectomy.
An entry is made just anterior to the scleral spur in the iris plane using a 27G needle. Using the inserter, the pre-loaded Ex-Press shunt is placed first turned horizontally. Once inside, it is turned 90 degrees to place it vertically. It should be inserted well away from cornea and with the back-plate flush against the scleral bed. The scleral flap is then closed to get a controlled flow and the conjunctiva is also closed.
Postoperatively, one of the complications is occlusion of the ostium with fibrin; however this can be cleared with Nd:YAG laser.
Ahmed Glaucoma valve (AGV)
The AGV is a valved glaucoma drainage device that has an opening pressure of 8mmHg. It is ideal for implantation in refractory glaucomas such as neovascular glaucoma, uveitic glaucoma, post failed trabeculectomy etc. The silicone model is preferred since it causes less inflammation with less Tenon cyst formation and better control of IOP.
The author’s personal preference is a posterior chamber placement of the AGV in order to avoid long-term complications such as endothelial decompensation – a complication reported after anterior chamber placement. The FP7 model is generally used in adults.
The device is primed by injecting BSS through the tube. The plate is then sutured 8-10mm posterior to the limbus between two recti, most commonly in the supero-temporal quadrant. A 5x5mm limbus-based 2/3 thickness scleral flap is created to provide postoperative tube coverage. Phacoemulsification and IOL implantation are proceeded with.
A 23G needle is then used to carefully create a sclerotomy about 1-1.5mm posterior to limbus in a plane between the iris and the anterior capsule. The tube is then trimmed and inserted in this retro-iridal plane. This is followed by sealing the flap all around the tube in a tight manner with the use of sutures. The conjunctiva is then closed. Phaco incisions may be sutured if leaking.
Dr Soosan Jacob is Director and Chief of Dr Agarwal’s Refractive and Cornea Foundation at Dr Agarwal’s Eye Hospital, Chennai, India and can be reached at email@example.com