What is the role of drainage implant surgery in the treatment of primary open-angle glaucoma (POAG)?

Updated: Mar 16, 2020
  • Author: Kristin Schmid Biggerstaff, MD; Chief Editor: Inci Irak Dersu, MD, MPH  more...
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Generally, this procedure is performed after multiple attempts at successful trabeculectomy have failed.

A tube is placed in the anterior chamber to shunt aqueous to an equatorial reservoir, and then posteriorly to be absorbed in the subconjunctival space.

Types of implants include Molteno, Baerveldt, Ahmed, and Krupin, as follows:

  • Most shunts function by allowing passive drainage of aqueous from the anterior chamber.

  • The Molteno implant consists of a silicone drainage tube, which is connected to 1 or 2 acrylic plates that are sutured to the sclera.

  • The Baerveldt implant is available with larger plates with increased reservoir size. The seton (tube) connected to the reservoir usually is tied off with an absorbable suture, allowing flow to initiate 4-6 weeks postoperative once some conjunctival wound remodeling has taken place, thereby reducing the risk of immediate postoperative hypotony.

  • The Ahmed and Krupin implants have 1-way valves, which are designed to maintain pressure above 8 mm Hg. These implants may reduce the risk of hypotony, a complication of nonvalved shunts in the early postoperative period.

Because of less numerous postoperative visits, tube shunts may be indicated as primary surgery when patients are unable to come as frequently for follow-up care (because of transportation, financial, or long-distance issues). This can be a particular concern in rural areas that cover large distances.

A valved shunt may also be indicated as primary surgery if a patient has a strenuous job or other activities that require strenuous exertion. Severe exertion may cause a significant Valsalva maneuver, significantly increasing venous pressure postoperatively, which could result in a delayed suprachoroidal hemorrhage and possible severe loss of vision.

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