Experimental implantation of epiretinal retina implants (EPI-RET) with an IOL-type receiver unit

The purpose of this paper is to investigate the surgical feasibility of implantation and long-term structural outcome of retina implant devices with an anterior IOL receiver, a connecting microcable and posterior segment epiretinal microcontacts. Implantation of epiretinal retina (EPI-RET) implants was performed as a one-step surgical procedure including phacoemulsification and pars plana vitrectomy in two adult rabbits. Implants were mechanically stabilized in an anterior position by the lens capsule and in the posterior segment by microtacks with a soft contact collar. Follow-up (6 and 9 months) included regular clinical examination, anterior and posterior segment photography and finally pathohistological evaluation. Implantation was uneventful in case 1 and complicated by vitreous space haemorrhage in case 2. At the end of follow-up, the retina was partially detached in animal 1 and subtotally detached in animal 2. Common features of tissue reaction in both cases were the formation of cyclitic membranes extending around and posterior to the anterior IOL receiver. In addition to that severe proliferations developed around microcables, microcontacts and microtacks forming a tissue capsule around posterior segment foreign materials. Retinal areas in contact to implant devices presented a severe structural damage and disorganization. Results of this preliminary trial suggest that the application of epiretinal prostheses with large diameter IOL receivers may be a critical issue and can give rise to an unfavourable outcome. Further systematic investigation ought to be performed involving a larger number of animals, modified implants and perhaps other species.