Fig. 13.7  Refillable ported controlled release device design showing extended delivery tube (element 530) to reach distal tissue target. The injection reservoir contains a stop plate (element 539) to prevent needle penetration. The stop plate further contains holes (element 538) to allow fluid diffusion. A rate-limiting permeable membrane (element 550) prevents injection of small foreign particles into the tissue. Reprinted from Watson (2005)

13.4.3  Episcleral Implantation for Trans-Scleral Delivery

Although injections into the anterior subconjunctival space have been a longstanding practice dating back to the 1950s, particularly for injections of antibiotics or steroids, the placement of drugs or devices in the posterior sub-Tenon’s space did not gain favor until the beginning of the new millennium following new investigations utilizing techniques to place a depot of the anti-angiogenic agent anecortave acetate above the macula (Slakter et al. 2002; Dahlin et al. 2003). Concurrent with the development of an injection cannula for placement of such suspensions, a solid silicone based

Fig. 13.8  Episcleral implanted device with drug reservoir connected to a cannula to deliver drugs through the pars plana to the vitreous. The injection port region above the drug reservoir has an angled and large surface area to facilitate needle placement for reinjections. Reprinted from Avery and Luttrull (1998)

device was also devised as a means to put a more controlled rate form of the drug near the macula (Yaacobi 2002; Yaacobi et al. 2003). This original device had a length that followed along the border of the lateral rectus muscle and allowed placement of a drug load above the macular region with a distal end that was accessible anteriorly near the limbus to allow for easy retrieval. Continued modifications of that device were subsequently designed (Fig. 13.11) to allow for refill from an anterior port position connected to pathways that would communicate fluid posteriorly (Yaacobi 2006a). Furthermore, recognizing the possible need to more broadly distribute drug throughout the eye posterior, as might be required in disease states such as dry AMD, a circumferential modification of the design was proposed by

Fig. 13.11  Refillable episcleral-placed silicone device for trans-scleral delivery of active agents. Fluid-conducting passageways are disposed within the device that is coupled to the anterior injection port. Reprinted from Yaacobi (2006a)

Yaacobi (2006b) allowing for fluid channels to carry drug from the anterior port position to multiple locations around the eye equator similar to an encircling silicone buckle (Fig. 13.12). In order to be positioned under the four rectus muscles, this device style is made as a band that is threaded under the muscles and then secured to itself using a sleeve which tethers the two ends.

Variations in the above concepts have subsequently been reported. Avery (2006) proposed a slightly different design but essentially followed a similar approach to the original concepts of Yaacobi, showing a device (Fig. 13.13) with an anteriorly located hollow funnel-shaped needle insertion section (see element 220 in Fig. 13.13) connected to a delivery tube extending posteriorly; the device also is positioned below the inferior oblique muscle. Franklin (2007) further discusses a refillable device approach using the same anatomical placement. However, the refill method is accomplished through a two-part design in which a disposable refill portion containing an implant at the distal end can be interconnected to a second base portion which is attached or sutured to the eye. Because of this connection to a permanently positioned base segment, the refill section containing the implant should contact the eye in the exact position as the previously removed disposable.

Episcleral devices which communicate from an anterior to posterior position are generally designed with the thought of bringing high levels of the drug closer to the macula. However, if high levels can be trans-sclerally delivered or if drug is