How is the scleral flap dissected 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

Scleral flap dissection

A partial thickness limbus-based scleral flap is outlined using the cautery tip or by indenting the sclera. The edges of the flap are cut with a sharp blade angled perpendicular to the globe. The flap is then lifted and dissected between scleral lamellae toward the limbus. Keeping the dissection in the same plane all the way to the limbus produces a flap of even thickness throughout. As the flap dissection approaches the cornea, the blade should be angled slightly anteriorly, following the curvature of the peripheral cornea, to avoid premature entry into the AC. Alternatively, a crescent knife can be used to cut a flap pocket before cutting the sides using scissors. The flap must be handled gently and grasped only at its edges. See the image below.

As the scleral flap dissection approaches the limb As the scleral flap dissection approaches the limbus, the blade should be angled more parallel to the corneal curvature (green dashed line arrow) to avoid premature entry or entry into the anterior chamber that is too close to the iris plane (red dashed line arrow).

The flap should be approximately one third to one half of the scleral thickness. A flap that is too thick could hamper aqueous flow and a flap that is too thin could become very fragile. The flap can be rectangular, triangular, square, or parabolic. There is no evidence of superiority of one flap shape over any other. The size of the flap varies, but, ideally, it should be around 2-3 mm radially by 3-4 mm wide. The minimum size of the scleral flap is such that there is at least a 1 sclerostomy wide space between the edge of the sclerostomy and the outer edge of the flap. See the image below.

The ideal flap size in relation to the sclerostomy The ideal flap size in relation to the sclerostomy. The distance between the flap edge and the sclerostomy edge should be greater than or equal to the width of the sclerostomy.

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