Minimizing axon bundle activation of retinal ganglion cells with oriented rectangular electrodes

Area of Science:

• Biomedical Engineering
• Neuroscience
• Ophthalmology

Background:

• Retinal prostheses aim to restore vision in degenerative diseases like AMD and retinitis pigmentosa.
• Current devices face challenges with unintended activation of retinal ganglion cells via axon bundles, causing distorted visual percepts.

Purpose of the Study:

• To investigate methods for achieving focal stimulation of retinal ganglion cells using electrical stimulation.
• To optimize electrode design and stimulation parameters for improved visual quality in retinal prostheses.

Main Methods:

• Calcium imaging was used to record retinal ganglion cell responses to electrical stimulation in explanted retinas.
• Rectangular electrodes with varying orientations relative to axon bundles were tested.
• Different stimulation waveforms and electrode configurations were analyzed.

Main Results:

• Narrow, rectangular electrodes oriented parallel to axon bundles achieved focal stimulation.
• Short (33 μs), anodic-first biphasic pulses enhanced focal stimulation selectivity.
• Optimal electrode-to-retinal separation (≥50 μm) and electrode length improved focal stimulation, while direct contact reduced selectivity.

Conclusions:

• A stimulation strategy using parallel-oriented, narrow electrodes and specific pulse parameters can achieve focal retinal ganglion cell activation.
• This approach is expected to enhance the quality of vision restored by retinal prostheses.
• Optimized stimulation parameters minimize unwanted axon bundle activation, leading to more precise visual percepts.