Emerging vision restoration technologies

The eye’s retina is the light sensitive part of the eyeball – converting light into electrical signals. Therefore, retinal diseases such as retinal pigmentosa (RP) or age-related macular degeneration (AMD) can be devastating – as they impair vision or lead to blindness.

There are various current strategies for sight restoration – such as retinal prostheses or electrode arrays. The damaged photoreceptors are bypassed to stimulate the remaining neurons (bipolar or ganglion cells) – connecting to the brain’s visual cortex, providing patients with artificial sight. Existing sight restoration technologies cannot directly copy the activities of the retina; therefore, approximation is used.

Many different avenues are being explored within the future of vision restoration technologies – such as brain implants and gene therapy.

Brain implants (by Second Sight), currently undergoing clinical trials, utilise an electronic chip to directly stimulate the visual cortex. In these trials, patients currently experience vision to play a “PacMan” like game.

Miniature magnetic coils are being developed to activate specific neurons. Sensory substitution systems are being developed as visual prostheses. These systems will work by converting visual input to auditory and somatosensory stimuluses.

Gene therapy is another method to transport light sensitive molecules into the retina. RP causes photoreceptors to die, however, the neurons that have signal relayed from photoreceptors, remain intact. Giving these remaining cells light sensitivity, the photoreceptors can be bypassed – providing partial vision restoration. Gene therapy cannot yet be compared to chip implants. Despite this, the technology is feasible and has been shown to improve vision in a trial at a 3-year follow-up. However, this was a small patient study with a specific leber congenital amaurosis (LCA) genotype. The Food and Drug Administration (FDA) have approved gene therapies to treat some retinal diseases – this is very promising for the future of vision restoration.

The NeuroPace Responsive Neurostimulator (RNS) and Orion visual cortical devices are examples of implanted devices into the visual cortex, creating phosphene patterns. This is a promising substitution for natural vision in blind people. A recent study showed timings of stimulation could be altered to create more complex visual perceptions.

These emerging technologies show great promise for the future of restoring vision in patients with retinal diseases.

Image caption: The above image shown the eye and where the retina and optic nerve are located.

References:
[1] Retina of the eye (anatomy, Functions & Associated Conditions) (2022) Vision Center. Available at: https://www.visioncenter.org/eye-anatomy/retina/ (Accessed: 12 February 2023).
[2] Brightfocus.org. 2022. The Latest Developments in Retinal Implants | BrightFocus Foundation. (online) A vailable at: <https://www.brightfocus.org/macular/article/latest-developments-retinal- implants> (Accessed: 12 February 2023).
[3] Farnum, A. and Pelled, G., 2020. New Vision for Visual Prostheses. Frontiers in Neuroscience, 14.
[4] Testa F, Maguire AM, Rossi S, Pierce EA, Melillo P, Marshall K et al.Three-year follow-up after unilateral subretinal delivery of adeno- associated virus in patients with leber congenital amaurosis type 2. Ophthalmology 2013; 120(6): 1283–1291
[5] Bosking, W., Beauchamp, M. and Yoshor, D., 2017. Electrical Stimulation of Visual Cortex: Relevance for the Development of Visual Cortical Prosthetics. Annual Review of Vision Science, 3(1), pp.141-166.
[6] Beauchamp, M.S. et al. (2020) “Dynamic stimulation of visual cortex produces form vision in sighted and blind humans,” Cell, 181(4). Available at: https://doi.org/10.1016/j.cell.2020.04.033.