Abstract
Abstract: :
Purpose: To develop a minimally invasive technique for ab externo subretinal prosthetic implantation. This approach, as opposed to an internal one, may minimize intraocular manipulation and subsequent intraocular complications. Methods: A polyimide strip (0.5 mm x 5 mm x 10 µm) was implanted in the subretinal space of Yucatan miniature pigs (n=18) and Dutch belted rabbits (n=20). A partial thickness scleral flap was dissected superonasally (9 mm posterior to the limbus in pigs; 7 mm in rabbits). A 3 mm scleral incision down to choroid was then created within the bed of the flap. The polyimide strip was inserted through the incision and choroid into the subretinal space. Variations in the procedure included: attempts to control choroidal bleeding with cauterization, topical epinepherine, or pre–operative photodynamic therapy; performance of pars plana vitrectomy; use of an intravitreal endoscope; creation of a retinal bleb localized over the scleral flap by injection of balanced salt solution and/or Healon; and use of a polyimide guide (3mm x 10mm x 75 µm) or a 7–0 Vicryl suture to assist implant placement. Fundus photos and histology were performed post–operatively as well as in one pig eye three months later. Results: The polyimide strip was implanted successfully, but sporadically, in 6 rabbits and 5 pigs. In the other eyes, complications included choroidal hemorrhage, incarceration of the retina into the scleral wound, penetration of the retina by the polyimide guide and/or strip, and placement of the strip beneath the retinal pigment epithelium or within the choroid. Histology at three months post–op revealed disorganization of the inner and outer nuclear layers overlying the implant, but preservation of the ganglion cell layer. Minimal fibrosis around the implant was evident. Conclusions: The ab externo method may minimize intraocular tissue manipulation. We are experiencing increasing success with this approach, partly through the creation of a retinal bleb to enlarge the subretinal space and the use of a polyimide guide to assist in implant placement. However, the technique is challenging, and further refinements are needed to enhance its reliability.
Keywords: retina • vitreoretinal surgery