Status of the Feline Retina After Five Years of Subretinal Implantation With an Artificial Silicon RetinaTM

Abstract

Abstract: : Purpose: Retinal prosthetics are designed to restore vision to patients with photoreceptor degeneration, like retinitis pigmentosa, by contacting the retina to directly stimulate the neural retina. Permanently–implanted devices need to have long–term biocompatibility and durability to be a viable treatment for retinal disease. We have previously demonstrated biocompatibility of the subretinal Artificial Silicon Retina (ASR^TM) device for up to 27 months in the normal feline retina (Pardue et al. 2001. Exp. Eye Res. 73,333–334). Here we describe results obtained in longer follow–up periods. Methods: Normal cats were implanted with ASR^TM devices backed with either an iridium oxide or a platinum electrode. Retinal function and implant activity was monitored by periodic ERG recordings. After three (n=3) or five (n=2) years follow–up, the eyes were enucleated and the retinas examined for changes in gross morphology as well as immunohistochemical labeling patterns of 3 primary neurotransmitters of the inner retina: glycine, GABA, and glutamate. Results: The continued presence of an implant spike during ERG recordings indicated that all implants functioned throughout the study period. The ∼20% decline in ERG amplitude that was previously noted to accompany surgery and the loss of photoreceptors directly overlying the implant was maintained and did not appear to progress with time. In areas adjacent and distant from the implant, retinas retained normal laminar structure with no signs of inflammation or glial reaction. Directly over the implant, there was loss of photoreceptor nuclei and remodeling of the inner retinal layers, including alterations in the distribution of neurotransmitter labels. Conclusions: The morphological changes above the implant appeared to be caused by the presence of the solid device in the subretinal space possibly related to the blockage of choroidal nourishment. The maintenance of normal function and structure in all other retinal areas indicate that the subretinal ASR^TM device is well–tolerated by the retina and is functional in vivo for as long as five years.

Keywords: retinal degenerations: hereditary • immunohistochemistry • electroretinography: non-clinical