Dexamethasone, a potent corticosteroid, has been shown to suppress inflammation by inhibiting oedema, fibrin deposition, capillary leakage, and phagocytic migration of the inflammatory response. Vascular Endothelial Growth Factor (VEGF) is a cytokine which is expressed at increased concentrations in the setting of macular oedema. It is a potent promoter of vascular permeability. Corticosteroids have been shown to inhibit the expression of VEGF. Additionally, corticosteroids prevent the release of prostaglandins, some of which have been identified as mediators of cystoid macular oedema.
After the plate is attached to the globe, the tube is laid across the cornea and cut with a sharp scissors to create a beveled edge with the opening toward the cornea. The tube should extend approximately to 3 mm into the anterior chamber to minimize the risk of tube-cornea touch or retraction out of the anterior chamber. A 23-gauge needle is used to create a track through which the tube is inserted into the anterior chamber just anterior and parallel to the iris. The tube may be secured to the sclera a few millimeters anterior to the plate with 7- 0 or 8-0 Vicryl suture. This suture helps to stabilize the tube and should not be tight; otherwise, it will restrict flow in valved devices.