Many different styles and sizes of tube implant devices exist but the basic implant technique is the same. A limbal peritomy is created, typically in the superior-temporal quadrant. Blunt dissection opens the potential space beneath Tenon’s capsule, taking care to avoid the rectus and oblique muscles. If the device is a “valved” implant, such as an Ahmed, it should be primed with Balanced Salt Solution® (BSS) or Ringer’s lactate to confirm that the valve is open. The tube plate(s) is then sutured in place using non-absorbable sutures, e.g. 6-0 black silk, so that the leading edge is 8-10 mm posterior to the limbus. Note that in children this may not be possible and distances of 5-7 mm are acceptable. In a microphthalmic eye, especially if less than 18mm in length, one must be careful that the plate does not touch the optic nerve. This can be accomplished by using a pediatric-sized device with anterior placement. Otherwise, adult size devices may be used. In some cases (e.g. Baerveldt), the implant plates can be trimmed to accommodate the smaller dimensions of some eyes or where retinal or other hardware complicates insertion.

A self-sealing paracentesis is always a good option so there is an alternative entry to the AC. The tube is then trimmed with bevel up so that when inserted it will extend 2-4 mm into the anterior chamber. A 22 or 23-gauge needle is used to enter the anterior chamber, just posterior to the limbus in a plane that is parallel to the iris. The tube is inserted through this opening such that it is touching neither the iris surface nor the corneal endothelium. If needed, air or viscoelastic may be used to reform the anterior chamber via the paracentesis, and may be left in the eye to help reduce the incidence of postoperative hypotony. As mentioned above, a means of occluding the tube in nonvalved implants is mandatory. Most commonly this is done using a 6-0 vicryl suture. The tube occlusion must be confirmed with Ringer’s lactate in a syringe using a 30 gauge needle or cannula.

The tube should be covered with a 4 x 6 mm patch of processed sclera or cornea (or with tissue dissected from a donor eye at the same sitting), banked dura or pericardium. If this type of tissue is not available, the entry into the anterior chamber may be created under a partial thickness, limbus-based scleral flap similar to that used for a trabeculectomy or trabeculotomy. Alternatively, a partial thickness scleral patch can be dissected from an area adjacent to the tube placement and used to cover the tube. When sclera in the host eye is still attached at the limbus, the tube entry should be directed somewhat posteriorly as it will be canted anteriorly when the flap is sewn back into place. Pars plana tubes are an option for aphakic children but the formed nature of the pediatric vitreous will lower success rates unless a total vitrectomy has been performed previously or will be done at the same time as the tube is placed.

After instilling atropine, antibiotic, and steroid ointments the eye is patched and shielded. Daily postoperative follow-up is recommended for at least the first several days as hypotony due to overflow or leak around the tube or even high IOP may occur. Early complications may include iris or vitreous in the tube, corneal touch by the tube, iritis, hyphema, conjunctival or scleral patch retraction, flat anterior chamber, or serous retinal detachment and choroidal effusion. The surgeon must be prepared to deal with these complications medically and/or surgically if they wish to undertake this procedure. Hypotony can often be managed by aggressive use of cycloplegics and simply waiting. Reformation of the AC using air or viscoelastic is sometimes needed. Removal of iris or vitreous from the tube can be delayed for 1-2 weeks while the tissues have a chance to heal.