Abstract
Purpose :
In patients with geographic atrophy, planar subretinal photovoltaic implants provided prosthetic acuity up to 20/440 – closely matching the 100mm pixels size. However, significant decrease of the pixel size is not possible due to fundamental limits of the electric field penetration depth with planar bipolar pixels. To overcome this limitation, we developed 3-dimensional implants: with pillar and honeycomb-shaped electrodes. In this study, we assess feasibility of safe removal of these implants for potential replacement with newer generation devices.
Methods :
Three types of the subretinal silicon-based implants have been studied: 1mm-wide devices with 25µm-deep honeycomb-shaped wells and pixel widths of 40, 30 and 20 µm; 1.5mm-wide devices with 35µm-high pillars with pixels of 30µm pitch; and flat photovoltaic PRIMA implants 1.5 mm in width from Pixium-Vision. Devices were implanted beneath the degenerate rat retina (RCS, p180-300), and the retinal integration was monitored by OCT imaging. After 6 weeks, the retina was detached and the devices were gently separated by subretinal BSS injection between the retina and implant and then removed. A new planar device was placed in the same location and allowed to recover for 6 weeks before eyes were collected for histology and immunohistochemistry analysis.
Results :
Retinal integration with 3-D implants was observed by OCT after 6 weeks. Device removal was successful with all three types of implants: flat, wells and pillars of all sizes, and OCT showed preserved retinal structure. Immunohistochemistry showed preserved bipolar cells with minimal glial scaring. Cellular residues on devices were identified as IBA1 positive cells, indicating microglial cells remaining on the implants after extraction. Re-implantation of the new devices in the extraction location demonstrated de nouveau INL integration with the new implant by OCT.
Conclusions :
Flat, honeycomb and pillar implants can be successfully implanted, explanted and re-implanted in a rodent model of retinal degeneration. The surgical steps are feasible, and the postoperative and histological follow-up showed good inner retinal preservation. In human eyes, such surgery should be easier compared to much smaller (5-6 mm diameter) rat eyes.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.