The nonpenetrating filtering procedure requires a functioning intrascleral space. This space is created after a careful dissection and resection of the deep scleral flap. In order to prevent a collapse of the remaining superficial flap that forms the roof of the intrascleral cavity, a space maintainer is usually inserted at this stage of surgery. Two different types of drainage devices are used: absorbable and nonabsorbable implants. The first type is currently made of porcine collagen material that is slowly absorbed over time, whereas the second is usually made of nondegradable materials that permanently remain in the scleral bed. No significant differences in the surgical technique can be found between the two types of implant. The long-term results are fairly similar for both of them, the absorbable implant being slightly more advantageous.