What is the role of antifibrotic agents in the performance of trabeculectomy?

Updated: May 18, 2020
  • Author: Maria Hannah Pia Uyloan de Guzman, MD; Chief Editor: Hampton Roy, Sr, MD  more...
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Answer

Antifibrotic agents

The use of antifibrotic agents is one of the major modern improvements on Cairns' original trabeculectomy. Antifibrotic agents, specifically 5-fluorouracil (5-FU), were first used postoperatively as subconjunctival injections by Heuer and colleagues in 1984 [5] to suppress scar formation and preserve the patency of the filtering fistula. Later, Chen introduced the intraoperative application of mitomycin-C (MMC). [6] 5-FU can be used both for intraoperative application and postoperative injection. [7, 8] The use of MMC as a postoperative injection has been reported [9] but is not as widely accepted as 5-FU.

Initially, antifibrotic agents were reserved only for high-risk cases [10] with preexisting conjunctival scarring, but they are now being used even for primary cases. Their use increases the success of trabeculectomy but also increases the risk of certain complications such as hypotony, bleb leak, shallow anterior chamber, and thin bleb. [11, 12, 13] The consensus of the World Glaucoma Association states that the risk benefit ratio of using antifibrotic agents should be assessed for each individual patient prior to use. [14]

Although both 5-FU and MMC are effective at improving trabeculectomy success [11, 12, 13] , some evidence shows that MMC-enhanced surgery achieves lower pressures [15] . However, it appears to be associated with a greater risk of complications. In February 2012, the FDA approved a specific mitomycin product (Mitosol) indicated for adjunct to ab externo glaucoma surgery. It is available as a kit that contains the lyophilized drug (0.2 mg/vial), as well as the diluent, sterile sponges, tuberculin syringes, disposal bag, and other needed equipment for the procedure.

The antifibrotic agent can be applied to the scleral bed before or after the scleral flap is cut. Any absorbent material or sponge that does not fragment when soaked (eg, instrument wipe or cellulose sponge) can be used to apply the antifibrotic agent. Contact of the antifibrotic agent with the wound edges should be avoided. The antifibrotic-soaked sponges should be applied to the area where aqueous flow is desired and should not be placed too close to the limbus in the case of fornix-based conjunctival flaps. After all the sponges have been removed, the site is irrigated with copious amounts of saline solution to remove any excess antifibrotic agent.

The concentration of 5-FU used intraoperatively is 50 mg/mL applied for up to 5 minutes. The concentration of MMC used intraoperatively ranges from 0.1-0.5 mg/mL applied for 2-5 minutes. The concentration and duration depend on the risk of failure in a particular case. Some surgeons prefer to keep the concentration constant while adjusting the duration while others prefer the opposite.

Recently, the alternative technique of intraoperative injection of MMC into the sub tenon space before the start of conjunctival dissection [16] has become popular. This technique avoids the use of sponges, saves time, and allows precise control of the dose of antifibrotic (usually 10-20 mcg).

Antivascular endothelial growth factor (anti-VEGF) agents have been used on filtering blebs, but the evidence of benefit or harm is still lacking. [17]


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