Models for Precision & Color in Argus II Retinal Implant

Article: Computer model fosters potential improvements to ‘bionic eye’ technology
Source: USC Keck School of Medicine, via NEI
Published: April 9, 2021
Article: USC research coalition uses computer models to advance benefits of ‘bionic eye’
Source: USC Allen and Charlotte Ginsburg Institute for Biomedical Therapeutics
Published: February 10, 2021 [Added November 15, 2021]

Fundus photo of the electrode array

The present pair of studies explored improvements to the Argus II retinal implant using electrical simulation wavefront models for greater precision of target stimulation as well as the encoding of basic color. The Argus II retinal prosthesis uses a camera mounted on special glasses to detect patterns of light. These signals are then relayed to an array of 60 electrodes that stimulate retinal ganglion cells (RGCs). The implant is used in patients whose photoreceptors no longer detect light, such as in severe cases of retinitis pigmentosa, by stimulating retinal ganglion cells downstream of the photoreceptors. The axons of retinal ganglion cells together form the optic nerve that relay the signal to the brain for visual perception. In some patients, off-target stimulation of the axons rather than the cell body results in the perception of elongated phosphenes rather than the intended dots of light. To address this issue, the researchers used a computer model of two types of retinal ganglion cells, D1-bistratified and A2-monostratified, at the single-cell level and in large networks. They identified a pattern of short pulses that preferentially targets the cell bodies with less off-target activation of axons. In a more recent study, the same team of researchers applied the same computer models to study the encoding of color by retinal ganglion cells. Prior tests in patients revealed that the perception of color depended on the frequency of electrical stimulation. The second study uses computer models to predict eliciting color perception, specifically by stimulating small bistratified cells that contribute to blue-yellow color opponency, i.e., blue and yellow color perception. These two studies provide information to guide improvements in the Argus II retinal prosthesis toward more precise and colorful visual perception for the blind.

My rating of these studies: ⭐⭐

Paknahad J, Loizos K, Humayun M, et al. "Targeted Stimulation of Retinal Ganglion Cells in Epiretinal Prostheses: A Multiscale Computational Study." IEEE Transactions on Neural Systems and Rehabilitation Engineering.  28(11):2548-2556. 29 September 2020. https://doi.org/10.1109/TNSRE.2020.3027560 [PDF]

Paknahad J, Loizos K, Yue L, et al. "Color and cellular selectivity of retinal ganglion cell subtypes through frequency modulation of electrical stimulation." Scientific Reports.  11(5177). 4 March 2021. https://doi.org/10.1038/s41598-021-84437-w