The port delivery system (PDS) is a permanent, refillable, intraocular implant that is designed to deliver ranibizumab (Genentech) in a continuous manner into the vitreous cavity. The PDS reservoir can then be refilled in the clinic setting every 6 months.

The PDS has a silicone septum and a wide flange. At the end of the reservoir, there is a titanium plate with channels that allow for the slow release of ranibizumab.

MAKING THE INCISION

Good exposure of the PDS implantation site is important. This involves a peritomy of the superotemporal conjunctiva at the limbus with dissection of tenon’s capsule. A relaxing incision should also be made. It is important to get adequate exposure and not have the relaxing incision too close to the intended implantation site.

Use a straight MVR blade to make a 3.5 mm wound 4 mm from the limbus. Carefully, make a lamellar dissection of the sclera exposing, but not incising, the choroid. Then, use an endolaser probe for edge-to-edge pars plana laser ablation, with 1-second-long duration single shots, overlapping without repeating. As you keep lasering, eventually you might see some bubbles of the vitreous percolating out.

Next, use a larger 3.2 mm straight-slit knife and go in once again, with the same direct, smooth motion and squared-off corners.

IMPLANTATION AND CLOSING

An injector is used to insert the PDS implant, which has a pre-filled reservoir with a 100 mg concentration of ranibizumab (Figure 1). It may be a tight fit, but you can gently rotate the implant in, and then, once it is inside as far as possible, release the implantation device from its holder, letting the clamps close. Then push it in a little bit more, so it is flush.

In order to prevent exposure of the implant, both tenons and the conjunctiva need to be closed over the implant. Care should be taken to bring the conjunctiva back to the limbus as well as closing the relaxing incision.

REFILLING THE PDS

The refill procedure for the PDS can be done in a clinic setting using a special refill injector. The process is not the same as a typical intravitreal injection. It is important to align the needle perpendicular to the face plate and centered in the septum. Ergonomically, it is recommended to do this in a contralateral position.

Visualization of the implant within the vitreous cavity can be done in order to see if your needle is aligned in the correct orientation. As you inject the medication, the refill device has a secondary chamber where the fluid in the reservoir is exchanged.

The PDS implant is currently in clinical trials. Although this is a new technique still undergoing investigation, careful attention to detail can ensure the successful—and safe—implantation of the PDS device. NRP