What are pearls for performing a scleral flap dissection 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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Scleral flap dissection

Minimal resistance from the scleral tissue when performing the lamellar scleral flap dissection toward the limbus indicates that the dissection is continuing in the same plane. Increased resistance indicates that different planes are being dissected. This makes dissection more difficult and could produce a flap of varying thickness.

Whenever possible, the sides of the scleral flap should not be cut flush to the limbus. The dissection of the scleral flap is continued as a short tunnel 1-2 mm beyond the anterior limit of the sides of the flap. This encourages aqueous flow posteriorly rather than along the limbus and it helps prevent limbal leaks when using a fornix-based conjunctival flap. However, this is difficult for beginners because the limbal landmarks are not easily visible. It is also not compatible with the blade or scissors technique of creating the sclerostomy and it may make the insertion of the scleral punch difficult. See the image below.

Diagram showing the ideal extent of internal disse Diagram showing the ideal extent of internal dissection under the scleral flap and the ideal extent of the flap sides (external).

Before inserting the punch under the flap and into the AC, apply pressure to the handle so that the cutting edges move closer together. This improves the steadiness of the punch as the cut is made.

Once the punch tip is inside the AC but before the cut is made, reorient the punch so that it is almost perpendicular to the limbus and tug gently. Resistance indicates that the lip of the internal incision is well engaged. This helps create a full-thickness punch with nonshelved edges. See the image below.

At the anterior limit of the scleral flap the blad At the anterior limit of the scleral flap the blade is redirected parallel to or towards the iris (green dashed line arrows, left). The "sclerostomy" is actually corneal tissue anterior to the trabecular meshwork/Schlemm canal (right).

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