Effects of Electrical Stimulation on Retinal Morphology as Seen with Optical Coherence Tomography

Retinal prostheses provide blind patients with the ability to detect motion and locate large objects. Future implants will require smaller electrodes to improve resolution, but increased charge density may result, creating a safety concern. We developed a novel in vivo method to study the effects of electrical stimulation in the retina using real time Optical Coherence Tomography (OCT) imaging combined with micropositioning a stimulating electrode. We observed that electrical stimulation settings with both pulse rates at and greater than 100 Hz as well as charge density 1.22 mC/cm2 and above resulted in retinal thickening within minutes of stimulation, that affected several retinal layers. We showed with statistical significance that the median difference between the retinal thickness before and after stimulation was different from zero. In summary, both high rate and high charge density were required to create retinal thickening. The stimulus levels at which thickening was noted in our study were significantly higher than the parameters currently used in humans.