Electrode-size dependent thresholds in subretinal neuroprosthetic stimulation.

Area of Science:

• Neuroscience
• Biomedical Engineering
• Ophthalmology

Background:

• Retinal prostheses offer partial vision restoration but struggle with object size identification.
• Subretinal electrical stimulation is a key technology in developing these prostheses.
• Understanding stimulation thresholds is crucial for optimizing prosthetic performance.

Purpose of the Study:

• To investigate electrode-size specific stimulation thresholds for subretinal electrical stimulation.
• To determine the variability of these thresholds in restoring visual perception.
• To establish guidelines for encoding object size using retinal prosthetics.

Main Methods:

• Utilized biphasic voltage-limited current stimuli delivered via a light-sensitive microchip.
• Determined threshold charge densities for varying electrode sizes in photoreceptor-degenerated mouse retinas (rd10).
• Recorded retinal ganglion cell spiking to identify stimulated neural activation.

Main Results:

• Stimulation thresholds ranged from 100-900 µC cm⁻² for small electrodes (30 µm diameter).
• Threshold charge density decreased with increasing electrode size, plateauing at 20 µC cm⁻² for electrodes >300 µm.
• This inverse relationship between electrode size and threshold was also observed in wild-type mouse retinas.

Conclusions:

• Electrode size is a critical parameter influencing stimulation thresholds in retinal prosthetics.
• Smaller objects may be encoded by activating specific retinal ganglion cells with diverse thresholds.
• Encoding larger object sizes can be achieved by reducing stimulation charge density.