Most of us take vision for granted, but about 21.5 million adult Americans have trouble seeing, even with glasses or other vision aids. The leading causes of blindness or low vision in the US are age-related eye diseases, and many of the treatments are in fairly early stages of research and development. It's not easy to replicate the functions of a retina, but here are just a few projects that are working on ways to restore vision with some interesting technologies.
If you'd like to read more awesome and interesting stuff, check out this unrelated (but not entirely random!) Techdirt post