Effects of asymmetric electrical pulse on retinal excitement for retinal prostheses

Abstract

Retinal prostheses for blindness electrically stimulate retinas with photoreceptor cell degeneration to evoke a pseudolight sensation (phosphenes). Biphasic symmetric pulses with charge balancing are commonly used for electrical stimulation in retinal prostheses. It has been reported that a charge-balanced biphasic asymmetric pulse can reduce the threshold for electrical evoked responses in cochlear implants. In this study, in order to determine the effectiveness of an asymmetric pulse, we applied single biphasic symmetric and asymmetric pulses transretinally to the eyeball of anesthetized rats. We found that the application of an anodal pulse with a shorter duration and a higher current amplitude evoked a large field response in the superior colliculus (SC) in comparison with a symmetric pulse with the same electrical charge. This result suggests that an asymmetric pulse with a short pulse duration and high current amplitude in the anodal phase is more effective for retinal prostheses than a symmetrical pulse with the same electrical charge.