Improving the spatial resolution of epiretinal implants by increasing stimulus pulse duration
Andrew C Weitz1, Devyani Nanduri2, Matthew R Behrend3
1Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA. Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, CA 90089, USA.
Science Translational Medicine
|December 18, 2015
Summary
Longer electrical pulses in retinal implants improve vision for retinitis pigmentosa patients. This novel approach creates focal spots of light, enhancing form perception by avoiding unintended nerve stimulation.
Area of Science:
- Ophthalmology
- Neuroscience
- Biomedical Engineering
Background:
- Retinitis pigmentosa causes blindness due to photoreceptor degeneration.
- Current retinal prosthetics use microelectrodes to stimulate retinal neurons, acting as pixels.
- A limitation is the unintended stimulation of retinal ganglion cell axons, causing perception of large light shapes instead of focal spots.
Observation:
- Calcium imaging was used in isolated retinas to map neural activation patterns.
- Different electrical stimulation protocols were tested to identify optimal parameters.
- The study focused on understanding how stimulation affects inner retinal neurons and ganglion cell axons.
Findings:
- Pulse durations two orders of magnitude longer than conventional methods were investigated.
- Extended pulse durations (25 ms) successfully stimulated inner retinal neurons.
- This approach avoided activating retinal ganglion cell axons, confining neural responses to the electrode site.
Implications:
- The findings suggest a new stimulation strategy for retinal prostheses.
- Achieving focal spots of light can significantly improve form perception for patients.
- This research could lead to enhanced visual acuity, with potential for 20/312 Snellen acuity demonstrated.
