Histopathologic findings after subretinal surgical implantation of the PRIMA neurostimulation system in patients with geographic atrophy

Abstract

Purpose : To report for the first time histopathologic characteristics following subretinal implantation of the PRIMA neurostimulation system in patients with geographic atrophy (GA) due to age-related macular degeneration (AMD). The system is a wireless electronic visual prosthesis designed to partially restore central vision in patients suffering from GA with foveal involvement by converting infrared light into electric current that stimulates cells in the inner retina.

Methods : A total of 38 patients were treated in the context of the prospective PRIMAvera study with a surgically placed implant in the subretinal space via an eccentric retinotomy. Two eyes and the respective non-treated fellow eyes from two patients who passed away during the study (2 and 18 months after chip implantation) could be obtained. After horizontal opening of the globes, the retinal implants were removed. Histopathologic serial sections (stained with hematoxylin-eosin and periodic acid-Schiff reaction) were correlated with the clinical in vivo and ex vivo images, with the fellow eyes serving as controls.

Results : Both removed implants revealed intact and functional chips, even after fixation of the globe in 4% paraformaldehyde. Histologically, the implants were located at the level of the outer nuclear and the outer plexiform layer. Residual photoreceptor nuclei and basement membrane deposits were found beneath the chip. At the chip-retina interface, there was only a limited tissue response. Furthermore, no significant infiltration of inflammatory cells was detected. The retina overlying the chip was comparable to the fellow eyes in most areas with limited focal atrophy of the inner retina 18 months after chip implantation.

Conclusions : Implantation of the wireless PRIMA chip did not result in a significant encapsulation or inflammatory response. The architecture of the inner retina overlying the chip revealed focal structural changes which could be attributed to the surgical procedure. Eighteen months after chip implantation viable retina overlying the implant was present. When new surgical techniques are introduced in ophthalmology, histopathologic analysis should be performed whenever possible as it can provide additional insights regarding wound healing, potential alterations of surrounding tissues, and surgical trauma. This information may help to refine the surgical procedure.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.