Scleral Flap Dehiscence

Following its introduction by Cairns in 1968, trabeculectomy quickly became the procedure of choice for the management of elevated intraocular pressure (IOP) inadequately controlled by medications, and it remains the gold standard today. This procedure’s popularity stemmed from dissatisfaction with the existing practices of the time, which typically involved full-thickness sclerectomy. Although quite effective at IOP reduction, an unguarded sclerectomy invited severe and often prolonged hypotony, with the associated risks of a flat anterior chamber, maculopathy, and suprachoroidal hemorrhage, to name but a few. Placement of the sclerectomy beneath a partial thickness scleral flap added much needed control to filtering surgery. Indeed, proper construction and suturing of the scleral flap are vital to preventing scleral flap dehiscence and promoting further surgical success, as the scleral “valve” provides the majority of the resistance to initial aqueous outflow, limiting the risk of early hypotony. There is no consensus on the size or shape of scleral flap required to produce effective IOP control. Surgeon preference is generally what was taught during training, with square, rectangular, trapezoidal, and triangular flaps all commonly employed. Although scleral flap shape is probably unimportant, the flap should be at least one-half to two-thirds scleral thickness to avoid tearing or avulsing the tissue and to prevent “cheese wiring” by sutures. Most surgeons prefer to hinge the flap as far forward as possible to ensure that the sclerectomy is created anterior to the scleral spur, avoiding the ciliary body. Extending the sides of the flap too far beyond the limbus, however, may result in excessive filtration and early hypotony. Recently, some have advocated leaving the sides of the flap short, not extending fully to the limbus, in order to force aqueous posteriorly and create a more diffuse bleb. In this case a wider flap may assist with proper anterior placement of the sclerectomy. In many cases, complications involving the scleral flap can be avoided by attention to risk factors preoperatively and careful handling of tissue intraoperatively. The most important risk factor for scleral complications is previous ocular surgery performed at the intended trabeculectomy site, particularly extracapsular cataract extraction.