Fig. 13.14  Refillable episcleral exoplant design forms a seal on the tissue without tight suturing. Bottom surface has opening to allow injected fluid reservoir to maintain direct contact with the sclera. Reprinted from de Carvalho et al. (2006). Copyright 2006 Association for Research in Vision and Ophthalmology. Reproduced with permission of INVESTIGATIVE OPHTHALMOLOGY­ & VISUAL SCIENCE in the format Other Book via Copyright Clearance Center

extremely potent, then a sufficient gradient might be established which could achieve necessary therapeutic concentrations at the macula. Furthermore for disease conditions which do not involve the macula or have etiology with loci more anteriorly, then it may not be a requirement to deliver drug to the far posterior. De Carvalho and colleagues (De Carvalho et al. 2003, 2005, 2006; Krause et al. 2005) have described an episcleral refillable device that is more anteriorly located to deliver therapy for retinoblastoma. In one style of the device, a flexible silicone reservoir that is secured by sutures forms a seal with the sclera (Fig. 13.14). On the side of the reservoir directly contacting the sclera is an opening permitting direct communication with a solution containing the active agent. The outer perimeter adjacent to the conjunctiva incorporates a knob that can be manually palpated to confirm the device location. Refill is accomplished via direct injection through designated port areas on the device. A similar style device was independently reported by Adamis et al. (2004).

13.4.4  Subretinal and Suprachoroidal Implantation

Theoretically, a cannulated episcleral device would be capable of delivering its contents to locations in the eye other than the anterior or posterior chambers. In a patent application in 2002 that was allowed 7 years later, Greenberg (2009) reported a design having a refillable multi-compartment reservoir which could be implanted

Fig. 13.15  Episcleral reservoir design with an attached cannula leading to the subretinal space. Reprinted from Humayun et al. (2006)

adjacent to the retina having a cable containing multiple feeder tubes run trans-scleral through the pars plana, terminating in the refill port. In a reverse of that sequence, Humayan and De Juan (2006) describe a device showing a refillable reservoir in the episcleral pars plana location and a cannula penetrating through to the vitreous and secured at its terminal end under the retina posteriorly (Fig. 13.15). These authors further propose that the reservoir for such a device could be led from either an epiretinal position (an unlikely spot for refilling) or within the lens capsule as a hollow ring configuration.

Recently, investigations have progressed evaluating the suprachoroidal space as a zone that can accommodate devices. The essential description of this approach has been presented by Peyman (2005) showing design concepts for locating devices anchored suprachoroidally in the anterior-most location. But in addition, posterior invasion of the suprachoroidal space can be accomplished by feeding specially designed cannulas like the iTrack™ (iScience Interventional™) from an anterior insertion point (Olsen et al. 2006; Yamamoto et al. 2007). Adaptations of a suprachoroidal cannula to an anterior reservoir have not yet been reported.