Glaucoma Drainage Device Surgery
Ann Shue, MD
Sharon F. Freedman, MD
PREOPERATIVE CONSIDERATIONS
Assess status of the conjunctiva.
Valved: Provides immediate IOP lowering, for refractory moderate to severe glaucoma, or if there is concern for low aqueous production as in uveitic glaucoma or after cycloablation. Avoid in Sturge-Weber-associated glaucoma.
Determine placement of tube—Assess anterior chamber depth, lens status, and if vitrectomized.
May need retina surgeon to perform vitrectomy for pars plana tube or anterior chamber in aphakic eye with high risk for forward vitreous movement.
Determine location of plate—Superior temporal and inferior nasal are preferred first and second-choice locations, respectively, followed by inferior temporal and superior nasal.1 In some cases, inferior nasal may be preferred for first GDD, to leave room for a superior trabeculectomy or larger nonvalved GDD in superior quadrants when the patient is older.
Manage patient expectations about IOP control:
With valved devices, there may be a hypertensive phase in 2-4 weeks.
With nonvalved devices, IOP likely will remain unchanged for 5-6 weeks.
Discuss risks of infection in short- and long-term, hypotony, elevated IOP, and need for additional surgery. Discuss that the goal of surgery is not to improve vision, but to preserve remaining vision. There is risk of further damage to vision or to the eye. There is a small possibility of inducing strabismus with or without diplopia, or worsening known strabismus.
SURGICAL PLANNING
Let the OR team know which materials are needed:
Patch graft: Recommend scleral patch graft for superior GDDs and corneal patch graft for inferior GDDs (for cosmesis).
GDD: Valved (Ahmed FP7, Ahmed FP8) or nonvalved (Molteno, Baerveldt 250 mm2 or 350 mm2).2
Instruments:
Sutures:
Dyed, polyglactin 6-0 on a spatulated needle (for tube ligature in nonvalved GDDs).
Dyed, polyglactin 7-0 on a spatulated needle.
Dyed, polyglactin 8-0 on tapered round needle.
Nylon 8-0 and 9-0 suture.
Needles: hypodermic 30 gauge × 1/2″ and hypodermic 23 gauge × 1″.
Sodium hyaluronate.
Locking hemostat.
0.12 forceps.2
Blunt Westcott scissors.
Needle driver, locking (2) for nonvalved implant.
Tenotomy hooks (2), large muscle hooks (2).
Nugent forceps.
Paracentesis blade.
AC maintainer (recommended in Sturge Weber glaucoma and other cases at high risk for damage if IOP spikes from retained viscoelastic).
Smooth curved forceps (2).
Needle driver, locking or nonlocking, to close conjunctiva.
Medications:
Povidone-iodine 5%.
Balanced salt intraocular solution (BSS).
Bupivacaine 0.75%, preservative-free.
Cefazolin 200 mg/mL subconjunctival injection (vancomycin 25 mg/mL if patient allergic to penicillin).
Dexamethasone 10 mg/mL, preservative-free injection.
If implanting a nonvalved GDD, recommend glaucoma medications including timolol if no contraindication, dorzolamide, apraclonidine for younger patients, brimonidine for older patients, and acetazolamide IV.
Antibiotic-steroid ointment.
Ahmed FP7 and Baerveldt (250 and 350 mm2) are the most commonly used GDDs in children. Pediatric Molteno and Ahmed implants are available (Ahmed Model S3 and FP8, Molteno M1); however, adult size implants are preferred when possible. Silicone Ahmed implants have been shown to have better long-term IOP control compared to polypropylene Ahmed models, but the outcome is unlikely to be determined by implant type, thus choice of implant depends on clinical scenario, availability, and surgeon’s experience.
SURGICAL PROCEDURE: GLAUCOMA DRAINAGE DEVICE IMPLANTATION WITH PATCH GRAFT (VIDEO 11.1)
Standard prep and drape for intraocular surgery, recommend drape to keep eyelashes out of surgical field.
FIGURE 11.1. Limbal traction suture placement for adequate quadrant exposure and avoidance of corneal damage from corneal traction suture. A. 7-0 double (or single)-armed polyglactin suture needle partial-thickness pass at limbus ˜90 degrees from the quadrant of GDD implantation (superotemporal in this case). B. After suture has been pulled to approximately the midway point of the suture, the same or other suture end can be passed partial-thickness at the limbus 180 degrees from the original pass. C. The two suture ends have been pulled up along with the central portion of the suture between the two limbal passes until they are approximately even. The ends have been tied, and the suture needles cut off. A locking hemostat has been clamped to the suture ends to maintain the position of the eye in the opposite quadrant of the GDD implantation. Viscoelastic has been instilled generously on cornea to prevent corneal abrasion as eye is manipulated.
Place traction suture—pass 7-0 double-armed polyglactin suture partial-thickness at limbus about 90 degrees from quadrant of implantation on either side (Fig. 11.1).
After positioning eye with traction suture and locking hemostat to expose quadrant of implantation, surgeon and assistant each lift the conjunctiva with 0.12 or Bishop-Harmon forceps 7-8 mm posterior to and parallel to the limbus. Conjunctiva will fold perpendicular to the limbus in between the forceps (Fig. 11.2A).
FIGURE 11.2. Conjunctival and Tenon capsule incisions. A. Assistant and surgeon are lifting conjunctiva up 2-3 mm with two forceps to create a radial conjunctival fold about 7 mm posterior to the limbus. B. Surgeon has placed blunt Westcott scissors with tips perpendicular to scleral wall and across the conjunctival fold. C. An adequate conjunctival incision has been created parallel to the limbus after one cut across the conjunctival fold. D. Assistant and surgeon now are lifting the exposed Tenon capsule up 2-3 mm creating a radial fold. E. Surgeon has placed Westcott scissors across the Tenon fold, ensuring the scissor tips are abutting the sclera perpendicularly. F. After one cut, the resulting incision through Tenon capsule exposes bare sclera. Assistant and surgeon continue to lift up the cut edges to facilitate extension of the incision with the Westcott scissors.
FIGURE 11.3. Gentle anterior dissection of Tenon tissue to limbus in preparation for tube placement. A, B. Closed blunt Westcott scissors being used with one edge pushing Tenon insertion anteriorly on sclera. C. Dry sponge also being used to push remaining adhesions anteriorly until bare sclera is visualized up to limbus.
With Westcott scissors perpendicular to the sclera wall, cut across the conjunctival fold between the forceps to create an incision parallel to the limbus (Fig. 11.2B and C).
Repeat the previous two steps to create a Tenon capsule layer incision identical to the conjunctival incision (Fig. 11.2D-F).
Recommend limbal-based incision (fornix incision) in children to decrease tube exposure risk and potentially preserve limbal stem cells.
Use a toothed forceps to lift the posterior edge of the Tenon capsule incision and blunt Westcott scissors to dissect posteriorly until there is sufficient space for the GDD plate to lie on the sclera; consider micro Westcott scissors to sharply dissect Tenon capsule from sclera if scarring is encountered, with care to preserve Tenon capsule and the conjunctival flap.
Next, use forceps and closed Westcott scissors, with or without a Weck-Cel sponge, to push the Tenon capsule adhesions anteriorly until the sclera is bare up to the limbus (Fig. 11.3).
Prepare GDD: flush device (insert 27G cannula on BSS syringe into tube tip and inject until BSS streams through plate (Fig. 11.4). For valved GDD, ensure that BSS stops flowing through the valve outlet almost immediately when injection stops. Then remove syringe and set plate aside in antibiotic soak.
If BSS continues to flow easily through the valved plate after discontinuing BSS injection, the valve mechanism of the particular GDD is inadequate (especially in cases where hypotony poses extra risk). Obtain and test a new GDD.
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