Non-Penetrating Glaucoma Surgery
A number of surgical techniques are classified under this heading including deep sclerectomy, viscocanalostomy and canaloplasty. The common feature of all these types of surgery is the lack of full-thickness incision into the inside of the eye. Instead, they aim to open and expose a structure called Schlemm’s canal, a circular passage that travels for 360 degrees around the front of the eye near the junction between the cornea (clear front part of the eye) and sclera (the white part of the eye). They lower intra-ocular pressure by increasing the flow aqueous through the natural pathways of the eye as well via a mechanism very similar to trabeculectomy (described above). These surgeries are only likely to work if the angle between the iris and cornea is open. Therefore, glaucoma in which this angle is closed should not be treated with this type of surgery.
- Deep Sclerectomy: This technique is similar to a trabeculectomy, except no full thickness drainage channel is created. Instead the dissection opens into Schlemm’s canal but leaves the trabecular meshwork intact. Fluid from within the eye then flows across the trabecular meshwork and is then dispersed along Schlemm’s canal, under the sclera and into the “bleb”. The intraocular pressure reduction achieved is slightly less than a trabeculectomy, however speed of recovery after surgery is often quicker and it has a different complication profile. For example, cataract and chronically low intraocular pressure (hypotony) are less frequent following deep sclerectomy.
- Viscocanalostomy: A clear jelly-like material called viscoelastic is injected into the Schlemm’s canal in an attempt to dilate it and increase the rate of fluid flow along it. This can be performed as a stand-alone procedure or in combination with other techniques such as deep sclerectomy.
- Canaloplasty: A fine suture is threaded along the entire circumference of the Schlemm’s canal and pulled taught. This opens the Schlemm’s canal and aids flow of fluid along it.