Whether or not this works is far from certain. Doctors are going to watch the woman's progress closely over the next year, and she may need up to three more treatments. The cells also can't adjust their light sensitivity the way a retina can, so a truly effective system might need video glasses that automatically tweak the image brightness as the wearer ventures indoors or outdoors. Even so, this promises to be a breakthrough -- it's less intrusive than the current solution, which implants a chip that stirs cell activity. Eventually, certain forms of blindness may be relatively easy to mitigate.