The ExPress Mini Shunt is a newer, non-valved device that was originally designed to provide a direct conduit from the anterior chamber to the sub-conjunctival space or bleb.
In comparison to the glaucoma drainage devices that use an ab externo procedure, ab interno implants, such as the Xen Gel Stent, are transscleral implants to channel aqueous humor into the non-dissected Tenon's space, creating a subconjunctival drainage area similar to a bleb [REF].