Sometimes she wonders, though: What if scientists came up with a device, similar to a cochlear implant for deaf people, that could help her to see again? At 58, Johnson still remembers the old Six Million Dollar Man television series — the one where the injured test pilot, Steve Austin, gets new bionic limbs and a left eyeball with a 20:1 zoom lens and infrared capabilities. “Wouldn’t it be weird if I could go from this point to that?” she says, laughing. “I would so do it.”

Scientists and engineers still are a long way from creating a visual prosthesis that works as well as a real human eye, let alone a superhuman one. Nevertheless, two Stanford research teams are making steady progress in what was once the realm of science fiction. One of their promising new devices, a bionic vision system based on photovoltaic implants, is awaiting approval for human clinical trials in Europe. A second system, based on in vitro studies of the retina, could be ready for animal testing within four or five years. Both inventions have the same goal: to give back some measure of sight to people like Johnson, who have progressive diseases of the retina — especially retinitis pigmentosa and macular degeneration.

Certainly the need is there. According to the National Institutes of Health, retinitis pigmentosa is the leading cause of inherited blindness, affecting 1 in about 4,000 people in the United States. As in Johnson’s case, the disease usually begins with a loss of night vision in childhood, and progresses to involve peripheral and then central vision, gradually robbing young people of the ability to read, drive, recognize faces and do routine daily tasks.

Macular degeneration, in contrast, is one of the leading causes of vision loss in Americans 60 and older. By 2020, the NIH estimates that as many as 3 million people in the United States may be living with various stages of the disease, which gradually destroys the densely packed light-sensitive cells, called photoreceptors, in the retina’s center, or macula. “Many of these folks are going to be losing their central vision,” says Chip Goehring, president of the American Macular Degeneration Foundation, “so it is absolutely vital that we have options for the restoration of sight, including biological and mechanical approaches — stem cell therapies for photoreceptor replacement, gene therapies to restore dysfunctional retinal tissues, and prosthetic retinas that can serve an even wider population of people with vision loss.”