What Can I Do After Trabeculectomy to Improve Its Success Rate?
Preoperative planning, including the use of intraoperative antifibrotics, and careful surgical technique may reduce the risks of complications and failure of trabeculectomy. There are also interventions in the postoperative period that may improve the success rate of trabeculectomy.
Postoperative Topical Corticosteroids
I find the most commonly underused postoperative intervention is topical corticosteroids. If you use topical corticosteroids for trabeculectomy in the same way that you routinely use postoperative corticosteroids for cataract surgery, you will greatly lower your trabeculectomy success rate. While the short-term use of topical corticosteroids may not be important in the success of cataract surgery, it is critical to the success of trabeculectomy.1 I taper topical corticosteroid therapy after cataract surgery according to the waning anterior chamber reaction, but in trabeculectomy I taper the topical corticosteroids according to the inflammation and injection visible in the conjunctiva overlying and surrounding the trabeculectomy site. The anterior chamber is often quiet within the first week after surgery, but the inflammation and healing that you are trying to moderate is in full swing in the conjunctiva at the surgical site. Some patients on maximal topical medical therapy and those with preoperative drug sensitivities stay injected for a surprisingly long time after surgery. A rapid, early taper allows excessive healing and a poor long-term success rate.
I prefer to taper the topical prednisolone acetate very slowly and in accordance with the redness at the surgical site rather than according to a rigid predetermined schedule. As an example, in a patient with moderate postoperative injection, I will often use prednisolone acetate every 2 hours for the first 2 weeks, followed by a slow taper over the next 6 weeks as the injection is resolving. In contrast, rapidly reducing the topical corticosteroids may be of benefit to patients with postoperative hypotony, in whom you would like to allow some healing to raise the intraocular pressure (IOP) slightly. In the first few postoperative days, hypotony and anterior chamber shallowing can also be managed with intracameral injection(s) of viscoelastic; I find they reduce the anterior segment inflammation, reduce risk of hypotony-induced complications, and enhance short-term and long-term success by enhancing bleb formation.
5-Fluorouracil (5-FU) was initially used in trabeculectomies at high risk for failure but now is used mostly to enhance the outcome of primary filters, after bleb needling (see below), or to slow rapid healing in eyes that already had an intraoperative application of an antifibrotic. I prefer to inject 5 mg (0.1 cc of a 50 mg/cc 5-FU solution) adjacent to the bleb, although others recommend injecting into the bleb or 180 degrees away. You should be sure to avoid 5-FU entering the anterior chamber to prevent toxicity to the endothelium and other anterior chamber structures. One advantage of 5-FU is its short half-life and a localized effect, so it can be titrated to the desired effect. Disadvantages of postoperative 5-FU include the inconvenience of injections for the doctor and patient, local toxicity including the development of corneal epithelial defects that require discontinuation of injections, and that the duration of the effect of 5-FU is shorter than the healing time for a trabeculectomy. I believe that 5-FU injections are effective in the first 2 weeks postoperatively and have little benefit thereafter. 5-FU requires special handling including disposal because it is a chemotherapeutic agent and is considered a toxic substance.
I often suture the trabeculectomy flap fairly tightly when performing a trabeculectomy with antifibrotics in order to reduce the risk of postoperative hypotony. I prefer to plan on releasing sutures in the early postoperative phase to compensate for variable patient healing, rather than trying to obtain a perfect IOP on the first day after surgery. You need to vary the timing of suture release according to the surgery performed. In general, in trabeculectomy patients without antifibrotic use, sutures should be released in the first week (maximum 2 weeks) for best effect. With the application of 5-FU intraoperatively or with postoperative injections, the best effect of suture release is also in the first 2 weeks. In contrast, in trabeculectomy with mitomycin-C (MMC), I prefer to avoid suture release in the first week or two after surgery and plan to perform most suture releases between postoperative weeks 2 and 6.
You can release sutures 1 of 2 ways: the first is to cut or lyse the sutures with a laser (a thermal laser of virtually any wavelength can be used, but red is preferred in the presence of subconjunctival blood) and the second is to place releasable sutures at the time of surgery. The advantage of releasable sutures is that they can be removed at the slit-lamp and therefore do not require moving the patient to a laser within your office or at another location. The disadvantage of releasable sutures is that after the first few weeks they tend to break off and not release. I prefer laser suture lysis in most cases to allow later suture release and because there are no sutures left in the cornea that can cause foreign body sensation.
Pressure on the globe, either through the eyelid or directly on the eye immediately adjacent to the scleral flap with a cotton-tipped applicator and topical anesthetic, can temporarily improve the flow of aqueous into the bleb. I like to see physical enlargement of the bleb either as or immediately after I apply pressure to confirm that the aqueous is going into the bleb (as opposed to egress through a wound leak). I use these maneuvers to lower the IOP on postoperative day 1, to assess the potential for overfiltration with suture release, and to temporize while avoiding suture release in patients at risk for hypotony. Many patients can be taught to perform digital massage through their eyelid to encourage filtration. I have them try it on my eye to make sure they are applying the correct amount of pressure; on their next visit, I check their IOP before and after they perform digital massage to confirm the maneuver is having the desired effect, but not too much! It is my impression that digital massage is generally ineffective after about 6 to 12 weeks.
Needling can be performed to treat encapsulated and failing blebs. I prefer to apply topical anesthetic, followed by an injection of a small amount of local anesthetic along the planned track of the needle or narrow blade used to puncture or cut the scar tissue encircling the bleb. An injection of MMC 20 minutes before needling2 or of 5-FU immediately after needling has been recommended by some authors to increase needling success. For the treatment of encapsulated blebs, medical therapy with aqueous suppressants should be used as initial treatment and needling should be limited to the small percentage of patients in whom IOP is not at least moderated with medical therapy.3
1. Araujo SV, Spaeth GL, Roth SM, Starita RJ. A ten-year follow-up on a prospective, randomized trial of postoperative corticosteroids after trabeculectomy. Ophthalmology. 1995;102:1753-1759.
2. Mardelli PG, Lederer CM, Murray PL, Pastor SA, Hassanein KM. Slit-lamp needle revision of failed filtering blebs using mitomycin C. Ophthalmology. 1996;103:1946-1955.
3. Costa VP, Correa MM, Kara-Jose N. Needling versus medical treatment in encapsulated blebs: a randomized, prospective study. Ophthalmology. 1997;104:1215-1220.