- 1.
What are the indications for trabeculectomy surgery?
Trabeculectomy is indicated when neither medical nor laser therapy sufficiently controls glaucoma progression and that progression is likely to diminish a patient’s quality of life. Because visual needs and vision-related quality-of-life characteristics differ, patients should be assessed individually before a physician decides to perform surgery. Physicians should consider the likelihood of success and risk of complications from surgery prior to proceeding. Trabeculectomy surgery can also be considered as a primary treatment, especially in eyes with severe glaucoma at presentation. Outcomes from a large trial comparing primary trabeculectomy with medication were comparable. A smaller study comparing trabeculectomy with glaucoma drainage devices did not reach conclusive evidence about which technique is best.
- 2.
What is the goal of glaucoma surgery?
The goal of glaucoma surgery is to lower the intraocular pressure (IOP) sufficiently to prevent or minimize further damage to the optic nerve and visual function while avoiding severe complications. The target reduction of IOP will depend on individual factors. In the Advanced Glaucoma Intervention Study, patients with severe glaucoma with an average IOP of 12 mm Hg after surgery had stable visual function after long-term follow-up. Because many patients with glaucoma do not have elevated IOP, the goal of glaucoma surgery is not to reduce IOP to less than 21 mm Hg, but to tailor the pressure to the patient’s needs and characteristics.
- 3.
How do we inform patients about the risks of trabeculectomy surgery?
The risks and benefits of glaucoma surgery and alternative options must be carefully outlined to all patients in language that is easily understood. It is imperative to explain clearly the remote possibility of blindness or loss of the eye owing to hemorrhage or infection. Discussion should include the possibility of sudden or permanent visual loss, failure to control IOP (which may be too high or too low), the need for repeated surgery, droopy lid, discomfort, and significant blurring (common for the first 2 weeks). Failure to control the IOP and need to restart medication is not uncommon. Other risks include late-onset infection and endophthalmitis (rare) or cataract (common).
- 4.
Describe the factors associated with failure of glaucoma filtering surgery.
Risk factors for the failure of filtering surgery include pigmented skin (nonwhite), younger age, intraocular inflammation, neovascular changes, shallow anterior chamber, previous trauma, dislocated lens, complicated cataract surgery, vitreous in the anterior chamber, inability to use corticosteroids, previously failed glaucoma surgery, previous retinal surgery, scarred or abnormal conjunctiva, and an inexperienced surgeon ( Fig. 19-1 ).
Figure 19-1
Failing filter with increased vascularization and inflammation surrounding the filtering bleb.
- 5.
Does a fornix versus a limbal–conjunctival approach affect outcome?
Fornix-based and limbal-based approaches produce similar results after trabeculectomy surgery regarding IOP control. With a limbal-based approach the risk of a wound leak is much smaller. However, this incision appears to increase the likelihood of having a thin avascular and localized filtering bleb ( Fig. 19-2 ) and possible bleb-related infections. If a limbal-based flap is chosen, it should be made sufficiently posterior so that the closure is at least 10 mm or more from the limbus. If a fornix-based flap is chosen, it is imperative to ensure that the closure is watertight. There are many ways to close a fornix-based conjunctival flap and it depends on surgeon preference. Most commonly individual 10-0 nylon mattress sutures or a running 8-0 vicryl suture are used. A wet fluorescein strip at the end of the case to check for leaks is useful.
Figure 19-2
Corneal dissection of bleb after a limbal-based trabeculectomy causing discomfort and astigmatism.
- 6.
What medications should be stopped before filtration surgery?
Patients should continue their systemic medications. Coumadin or other blood thinners do not necessarily need to be stopped. However, it is convenient to confirm that the anticoagulation levels are within therapeutic range for the patient’s condition. If the surgeon desires to stop the Coumadin prior to surgery, it is imperative to discuss this with the patient’s internist, as in some cases stopping may not be advisable because of increased systemic risks.
- 7.
What are the choices of anesthesia?
General anesthesia is used in children and other patients unable to cope with a local anesthetic procedure. Sub-Tenon’s or subconjunctival anesthesia are our preferred choices. If a surgeon prefers regional anesthesia, peribulbar block is preferred to retrobulbar techniques. A detailed description of our current technique (“blitz” anesthesia) is as follows.
First, Xylocaine 1% jelly or lidocaine hydrochloride 2% jelly is placed in the fornix before surgery. In the operating room, a paracentesis is made temporally and a small amount of aqueous is released from the anterior chamber, followed by an irrigation of 0.1 mL of 1% nonpreserved lidocaine into the anterior chamber through a cannula. Next, inject a 1:1 mixture of 0.1 cc nonpreserved 1% lidocaine mixed with 0.1 cc mitomycin C (0.4 mg/cc). The total volume of 0.2 cc is injected under the conjunctiva with a 30-gauge needle. This precedes the formation of either a limbal- or a fornix-based flap. If using this method, additional lidocaine is usually not necessary, but can be used at the surgeon’s discretion. For a fornix-based conjunctival flap, an initial cut is made at the limbus, and 0.5 mL of anesthetic is injected with a cannula under the Tenon’s layer both temporally and nasally. With a limbal-based flap, a 30-gauge needle is used to inject 0.5 mL, 10 mm posterior and parallel to the limbus, ballooning the Tenon’s capsule and conjunctival space in both the nasal and the temporal direction. When closing either a limbal- or a fornix-based flap, additional lidocaine 1% is irrigated through the Tenon’s capsule so the patient has no discomfort.
- 8.
Does a triangular versus a rectangular flap affect outcome?
No. The shape of the scleral flap is surgeon-dependent; there is probably no difference in clinical outcome with a triangular or rectangular flap. Although the shape of the flap is not important, its thickness may be. Thin flaps may offer better long-term filtration. However, very thin flaps should be avoided if mitomycin C is used. Regardless of the shape of the scleral flap, sufficient sutures are necessary to be able to control the outflow and prevent overfiltration.
- 9.
Does the size of the internal block affect outcome?
No. A small (e.g., 1 mm) excision is sufficient, although some surgeons choose to create larger fistulas. Increased filtration results when one edge of the internal block coincides with one edge of the scleral flap. The internal block can be removed with Vannas scissors or a punch. Alternatively, a drainage implant under the scleral flap (Express) may be used.
- 10.
Are iridectomy and paracentesis always necessary during filtration surgery?
An iridectomy is always performed in angle-closure glaucoma to ensure that pupillary block does not occur. In addition, if the chamber shallows, the iris is less likely to occlude the ostium. However, iridectomy may not be necessary in patients with open-angle glaucoma and particularly in pseudophakic eyes. A paracentesis is always done, and it can be made with either a sharp blade temporally or a 27-gauge needle on a syringe. A paracentesis is considered essential with each procedure because it allows re-formation of the anterior chamber toward the end of surgery. By refilling the anterior chamber via the paracentesis, the surgeon has an appreciation of how much leakage is visible around the edges of the scleral flap.
- 11.
How tight should I make the scleral flap?
The number of sutures and their tightness depend on the diagnosis, preoperative IOP, architecture of the scleral flap, location of the fistula, and how much leak is desired at the time of surgery. In general those patients at high risk for complications associated with hypotony should have tighter scleral flaps. For example, patients with inordinately high IOP, shallow anterior chamber, angle-closure glaucoma, aphakic glaucoma, or increased episcleral venous pressure are more likely to develop complications if there is overdrainage.
With low-tension glaucoma, looser sutures with more flow may be indicated to ensure a low initial postoperative intraocular pressure. The sutures can be lysed with an argon laser anywhere from day 1 through the first 2 weeks or longer if antimetabolites are used.
- 12.
Are releasable sutures necessary?
Although releasable sutures have some advantages, they are not necessary to achieve a good result. We tend to use additional releasable sutures as they allow tighter closure of the scleral flap, avoiding hypotony, and because of the ease with which they can be removed at the slit lamp ( Fig. 19-3 ). The flap can be closed moderately loosely with permanent sutures, and the releasable sutures decrease the flow further. Selective removal between the first postoperative day and 1 month can easily be done at the slit lamp.
Figure 19-3
Low diffuse bleb with releasable suture in place 1 week following a trabeculectomy.
- 13.
Does it matter how far I dissect the scleral flap anteriorly?
We aim to open the fistula anterior to the trabecular meshwork. In large myopic eyes, a perpendicular incision just anterior to the corneoscleral sulcus carries the flap well anterior to the trabecular meshwork. In removing the internal block, a satisfactory fistula results. In contrast, in small hyperopic eyes and those with angle-closure glaucoma or peripheral anterior synechiae, an incision at the same point terminates just in front of the iris root. In these patients, an anterior dissection well into the cornea is necessary both to ensure that the fistula will not be blocked by uveal tissue and to prevent bleeding ( Fig. 19-4 ).
