Status of the feline retina after subretinal implantation of an artificial silicon retina for three years
 
MT Pardue, PhD; SL Ball, PhD; AY Chow, MD; JI Perlman, MD, PhD; EB Stubbs Jr., PhD; VY Chow, MS; NS Peachey, PhD
 
Atlanta VA Medical Center, Cleveland VA Medical Center; Optobionics Corporation, Hines VA Medical Center
 
Objectives: The artificial silicon retina (ASR) consists of an array of photodiodes that are designed to replace photoreceptors in patients that have retinal diseases in which only the photoreceptors degenerate. This retinal prosthetic, which is designed to lie within the subretinal space, is powered solely by incident light and requires no external power supply. In order to evaluate the feasibility, biocompatibility and functionality of placing an ASR in the subretinal space, a cat model has been developed. In cats followed for one year post-operative, the ASR maintains a stable position, continues to generate electrical current in response to light, and does not induce overall tissue rejection. However, in the retina immediately overlying the ASR, photoreceptors degenerate and changes are also observed in the inner retina. The present work evaluates cats implanted for 3 years to determine if the ASR will continue to function and if any progressive changes occur in retinal appearance.
 
Methods: A total of 8 cats were implanted with a 1.8 mm solid disk ASR and followed for 3 or more years post-operatively. Implant durability was examined by recording the electrical response of the implant to infrared light. The overall status of the neural retina was assessed by electroretinography using white light stimuli. Fundus photos were taken every 2 months to document implant position and to evaluate retinal health. At 36 months, cats were sacrificed, and eyes were enucleated and fixed for plastic embedding. Sections (0.5 micron in thickness) were stained with toluidine blue and examined.
 
Results: The ASR remains in a stable location and continues to function electrically for 3 years. The overall retinal appearance resembles that of cats examined at 1 year post-operative, indicating no progressive deterioration of retinal anatomy due to the presence and activity of the ASR.
 
Conclusions: These results further support the idea that an ASR can be implanted in patients long-term without deleterious effects.
 
Funding acknowledgment: This study was funded by the VA Rehabilitation Research and Development Service, project C2675CA.