How is conjunctival incision and dissection performed during 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

Answer

Conjunctival incision and dissection

Inflammation causes scarring and closure of the newly created fistula. Gentle handling of the conjunctiva is essential to reduce inflammation. Sharp scissors for cutting the conjunctiva and nontoothed forceps for grasping the conjunctiva are needed. The Tenon capsule, and not the conjunctiva, should be grasped whenever possible.

The conjunctival incision can be made at the limbus (fornix-based conjunctival flap) or away from the limbus (limbus-based conjunctival flap). There is no clear evidence for the superiority of one type of conjunctival flap over the other, [2] but the resulting bleb tends to be more localized and elevated in limbus-based flaps. [3]

The advantages of a fornix-based flap are the relative ease of achieving good scleral exposure and the absence of a scar that could potentially limit the posterior flow of aqueous. The disadvantage of a fornix-based flap is the relative difficulty of ensuring a watertight closure at the limbus.

The advantage of a limbus-based flap is the relative ease of achieving a watertight closure. The disadvantages are the potential for scarring at the incision site, which would limit aqueous absorption to the area anterior to the incision. It also creates difficulty exposing the sclera during the procedure. This difficulty can be reduced by using a Tenon traction suture. [4]

When performing a fornix-based flap, the conjunctiva needs to be cut close to the limbus but not so close as to injure to the limbal stem cells. Avoid leaving large, irregular conjunctival tags that could interfere with scleral flap dissection. A small radial relaxing incision can be made at one or both ends of the limbal incision, if needed. Without dissecting the conjunctiva excessively, the Tenon capsule insertion, which is located approximately 2 mm away from the limbus, is exposed and Tenon capsule is released from its insertion. The dissection is then carried out in the sub-Tenon plane. There is no need to separate the conjunctiva from the Tenon capsule.

An alternative to a pure fornix-based conjunctival flap is to leave a narrow conjunctival skirt approximately 1 mm wide attached to the limbus. This allows for a more watertight conjunctiva-to-conjunctiva closure and is less harmful to the limbal stem cells.

When performing a limbus-based flap, the conjunctiva and Tenon capsule are incised as far away from the limbus as possible. Ideally, this is done approximately 8-10 mm from the limbus. Closer than that could cause scarring too close to the scleral flap. Further than that makes exposure of the limbus very difficult. Some surgeons prefer to incise the conjunctiva and Tenon simultaneously while others prefer to do it in layers.

The conjunctiva and Tenon capsule are dissected away from the episclera and sclera. Separating the episclera from the sclera should be avoided to prevent persistent bleeding and scarring. Westcott scissors are used to bluntly dissect large sub-Tenon pockets in the preferred direction of aqueous flow (posterior).

Light cautery is used to achieve hemostasis. Excessive cautery should be avoided to prevent contraction or shrinkage of the scleral flap.


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