Continuous electrical stimulation decreases retinal excitability but does not alter retinal morphology

Area of Science:

• Neuroscience
• Biomedical Engineering
• Ophthalmology

Background:

• Retinal prostheses aim to restore vision via electrical stimulation.
• Understanding stimulation safety is crucial but less studied in the retina compared to thresholds.
• Previous safety studies often focused on neural structures other than the retina.

Purpose of the Study:

• To investigate the effects of continuous electrical stimulation on retinal morphology.
• To assess the impact of continuous stimulation on electrically evoked responses in the superior colliculus.
• To determine the safety limits of retinal stimulation in a rodent model.

Main Methods:

• Continuous electrical stimulation of the retina in a rodent model for 1 hour.
• Histological examination of retinal morphology post-stimulation (3-14 days later).
• Measurement of electrically evoked responses in the superior colliculus.

Main Results:

• The retina tolerated 1-hour stimulation with only minor histological changes observed.
• Stimulation at charge densities above platinum's safe limit (0.68 mC cm(-2)) at 300 Hz was tolerated.
• Continuous stimulation led to an elevated response threshold in the superior colliculus, suggesting adaptation.

Conclusions:

• The retina demonstrates resilience to prolonged electrical stimulation within the tested parameters.
• Continuous retinal stimulation induces adaptive changes in downstream neural pathways, like the superior colliculus.
• These findings inform the development of safer and more effective retinal prostheses.