How is aqueous flow increased following trabeculectomy?

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

If the flow through the scleral flap seems inadequate in the first few days postoperatively (ie, high IOP) and obstruction of the internal opening has been ruled out by gonioscopy, measures to increase the flow through the flap can be used. These include digital pressure (ocular/digital massage) and release of sutures (laser suture lysis or releasable sutures).

Digital pressure is applied to the eye either at the limbus opposite the trabeculectomy site or adjacent to the scleral flap. Bleb elevation and lowering of IOP indicate that aqueous has flowed through the flap. Lack of response to this measure could indicate scleral flap adhesion to the scleral bed or conjunctival adhesion to the sclera. Digital pressure is mostly used as a diagnostic measure prior to performing another method of increasing flow but is sometimes used as a therapeutic measure (ie, the patient is taught to do it a few times a day). When digital pressure is used therapeutically, most surgeons prefer to use it only temporarily to help the bleb form during the maturation period, while others also use it as a long-term adjunctive IOP-lowering measure.

Laser suture lysis (LSL) is performed using an argon laser and a suture lysis lens. The conjunctiva is compressed with the lens until the suture becomes visible. A very small spot size (50 microns) of high power (300-800 mW) and short duration (0.02 sec) is then used to cut the flap suture through the conjunctiva. This method is not effective in eyes with severe conjunctival chemosis, congestion, or hemorrhage.

Release of sutures is simpler than LSL because it can be done at the slit lamp and it can be done even if the flap sutures are not visible under the bleb. All it requires is that the releasable suture was placed properly with a portion left outside the conjunctiva for easy access.

Both LSL and release of sutures should be done in the first 2 weeks after surgery (up to 4 wks if intraoperative mitomycin-C was used). Only one suture should be lysed or released at a time to reduce the risk of a sudden drop in IOP. Immediate elevation of the bleb and lowering of IOP indicate a successful suture release. Occasionally, gentle application of digital pressure is needed immediately after the suture release if adhesions have developed around the scleral flap.

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