Stimulated sight

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Science Translational Medicine  13 May 2015:
Vol. 7, Issue 287, pp. 287ec75
DOI: 10.1126/scitranslmed.aab3974

By stimulating a small population of surviving neurons, a retinal prosthesis can give sight back to patients with degenerative eye diseases. There are two clinically approved retinal prosthetics in use today: an epiretinal system (ARGUS II) targeting retinal ganglion cells, and a subretinal system (Alpha IMS), targeting inner retinal neurons. Although promising, both systems fail to achieve visual acuity levels better than 20/1000—in essence, an individual needs 50x magnification when compared with normal vision. These systems also require bulky implanted electronics accompanied by cables exiting the eye. Lorach et al. now report a promising, fully implanted alterative whereby pulsed light activates retinal neurons, restoring sight in rodents.

The authors placed tiny photovoltaic arrays (1 to 2 mm in width) under the retina. These electronics were designed for both image capture and wireless data transfer, thus eliminating the need for trans-scleral cables. The spatial resolution of the retinal response was first explored in vitro, then the corresponding visual acuity was tested in vivo with both normally sighted and blind rats. Compared with natural light, the electrical receptive fields of the device were similarly highly localized. The photovoltaic arrays produced retinal responses in rats with retinal degeneration with an average spatial resolution of 64 µm, corresponding with half of the normal visual acuity in healthy rats. Similar to how distinct frames of a projected film appear steady, the retinal responses to prosthetic stimulation exhibited this “flicker fusion.”

Although Lorach et al. focused on an animal model of retinal degeneration, the translational relevance of this work is clear: Only through easily implantable, wireless systems that most closely mimic natural human processing can the functional restoration of sight in patients blinded by retinal degeneration be achieved.

H. Lorach et al., Photovoltaic restoration of sight with high visual acuity. Nat. Med. 10.1038/nm.3851 (2015). [Abstract]

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