Improving the resolution of restored vision


In a nutshell: A new strategy for electrically stimulating retinal cells may help retinal prostheses to deliver sharper vision.

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Improving the resolution of restored vision

Several diseases of the retina – the area at the back of your eyeball where light-sensitive cells are found – can lead to partial or even total blindness. In retinitis pigmentosa and age-related macular degeneration, for example, retinal cells are slowly damaged or lost over time. As a result, the cells become less able to absorb light and convert it to biological signals for the brain to process.

Retinal prostheses have restored some vision in people with retinal diseases by electrically stimulating the surviving cells, enabling them to send visual signals to the brain. However, the restored vision often has a low resolution, so it’s not sharp enough for important tasks such as recognising faces.

Ideally, each retinal cell would be stimulated individually, which means that improved vision would require a prosthesis with many electrodes that are as close in size to the cells as possible. Precise patterns of electrical stimulation waveforms have also been shown to provide clearer vision.

To increase the resolution of retinal prostheses, Brain Function CoE investigators from the University of Melbourne studied the best way to stimulate retinal cells. The team, led by postdoctoral researcher Wei Tong in Michael Ibbotson’s laboratory, used a diamond-based electrode array, which has more electrodes than existing prostheses.

The researchers stimulated retinal cells in rats with or without retinal disease, varying the duration of the electrical pulse from one-thirtieth of a millisecond up to 50 milliseconds. They also compared the effect of different ‘return’ locations. Returns are pieces of wire that stop the electrical current, limiting the area stimulated by each electrode. The returns were positioned either close to the electrode (local return) or further away from it (distant return).

The researchers found that the most effective strategy for directly stimulating a specific region of the retina used short electrical pulses – as brief as one-tenth of a millisecond – in combination with a local return.

The stimulation strategy developed in this study will be used in the ‘Diamond Eye’, a diamond-based retinal prosthesis that is expected to undergo clinical trials in the next few years.

Next steps:
The team is working to develop their stimulation strategy, which they plan to test in larger animals.

Tong, W., Stamp, M., Apollo, N.V., Ganesan, K., Meffin, H., Prawer, S., Garrett, D. J., Ibbotson, M. R. (2019). Improved visual acuity using a retinal implant and an optimized stimulation strategy. Journal of Neural Engineering. doi: 10.1088/1741-2552/ab5299

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