Abstract
Purpose :
For high-resolution prosthetic vision, pixels should be small, and crosstalk should be low. However, shallow penetration of the electric field with planar bipolar pixels prevents sufficient neural stimulation within the safe charge injection limit for pixels under 40μm. To overcome such limitation, we developed 3D arrays with deeper penetrating field and investigated the functional integration of these structures with the retina in vivo.
Methods :
3D implants were constructed by polymerizing honeycomb-shaped 25μm tall walls on planar photovoltaic arrays of 40μm and 20μm pixels, with a common return electrode on the edge of each device. Following subretinal implantation in rats with degenerated retinae (RCS rats), visually evoked potentials (VEPs) were measured in response to pulsed NIR (880nm) activation of the implants. Stimulation threshold was measured with full-field illumination, while visual acuity was assessed using alternating gratings, utilizing current steering-based field confinement. To verify the long-term effects, the VEP performance was followed up for at least 32 weeks post-op.
Results :
Bipolar, horizontal and glial cells migrated into the honeycomb-shaped wells of both sizes. The full-field stimulation threshold with 3D implants was around 0.06mW/mm2 with 10ms pulses - the same as with their flat counterparts, independent of the pixel size. The threshold remained nearly constant over the follow-up period. The VEP amplitude at high irradiances (2-5mW/mm2) usually exceeded 100μV on the day of implantation, dropped drastically to a few tens of μV after a week, and gradually recovered to the initial level, if not greater, in approximately 15 weeks. Grating acuity matched the row pitch with 40μm pixels. With 20μm pixels, the prosthetic acuity matched the natural resolution of rats: 27.9 +/- 2.8μm.
Conclusions :
Retinal integration with 3D implants did not adversely affect its electrical excitability. The stimulation threshold and visual acuity with 3D arrays were not different from those measured with flat arrays, utilizing current steering-based field confinement. If successful in human patients with atrophic macular degeneration, 3D honeycomb-shaped implants with 20μm pixels may enable prosthetic visual acuity as high as 20/80.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.