High-Resolution Electrical Stimulation of Primate Retina for Epiretinal Implant Design

Abstract

The development of retinal implants for the blind depends crucially on understanding how neurons in the retina respond to electrical stimulation. This study used multielectrode arrays to stimulate ganglion cells in the peripheral macaque retina, which is very similar to the human retina. Analysis was restricted to parasol cells, which form one of the major high-resolution visual pathways in primates. Individual cells were characterized using visual stimuli, and subsequently targeted for electrical stimulation using electrodes 9 -15 m in diameter.

Upper threshold of extracellular neural stimulation

“…In all of these applications, the characteristics of the stimulation waveform (principally the amplitude, polarity, and pulse width) play an important role in the design of a particular prosthetic device, making it critical to understand the relationship between stimulation threshold and pulse duration. Electrical stimulation of the retinal ganglion cells (RGC), used in epiretinal prostheses, was extensively studied by several research groups (Fried et al 2006;Jensen et al 2003Jensen et al , 2005Sekirnjak et al 2006Sekirnjak et al , 2008Stett et al 2000Stett et al , 2007Tsai et al 2009), and the strengthduration relationship has been experimentally measured (Jensen et al 2003(Jensen et al , 2005Sekirnjak et al 2006;Tsai et al 2009) and modeled computationally (Boinagrov et al 2010;Greenberg et al 1999). The strength-duration relationship defines for a given pulse duration the minimum stimulus strength, or stimulation threshold, above which an action potential (AP) is generated.…”

A Treatise of the Physical Aspects of Phosphenes and Single-Cell Selectivity in Retinal Stimulation

“…These findings indicate that ON and OFF type cells fire temporally in phase [74]. ON and OFF type cells can be stimulated with arrays of electrodes with small diameter at comparable threshold levels [71]. Margalit [75] reported similar findings in tiger salamander retina.…”

“…Despite that ON and OFF type ganglion cells exhibit different light-response properties [68], retinal connectivity [69] and dendritic tree breadth [70], the activation threshold for these two cell types is not statistically different both for epiretinal [71] and subretinal [72] stimulation. Experimental findings by Jepson [73] indicated similar thresholds for electrical stimulation of the five numerically dominant retinal ganglion cell types previously mentioned.…”

“…This is because ON and OFF type cells are spatially intermixed [78] and the bright response of ON type cells overshadows the response of OFF cells and their activation is more preferred [74]. While the stimulus is delivered to the cells, the activation area can indicate the stimulation of RGCs regardless of the type and class because they have similar activation thresholds [71][72][73]. ON and OFF type cells are contained within the activation area.…”

Electronic restoration of vision in those with photoreceptor degenerations

“…Electrodes that are close to their target cells require less current for stimulation. 56,86 The distance of the stimulating electrode from the target cell, rather than the electrode size or tissue impedance, is the most important factor in designing an electrode that uses less current to generate a response. 22 Designing an implant that uses less current to elicit a response is important as high current injection could be problematic in terms of tissue heating and damage over time.…”