The Israel-based company Nano Retina and others are developing early-stage devices and implants that restore partial sight to the blind. Nano Retina uses a tiny sensor backed by electrodes embedded in the back of the eye, on top of the retina. They replace connections damaged by macular degeneration and other diseases. So far images are fuzzy and gray-scale and a long way from restoring functional eyesight. Scientists, however, are currently working on ways to mimic and improve eyesight in people and in robots that could lead to far more sophisticated technologies.

Engineers at companies like Ekso Bionics of Richmond, Calif., are building first-generation exoskeletons that aim to allow patients with paralyzed legs to walk, though the devices are still in the baby-step phase. This summer the sprinter Oscar Pistorius of South Africa proved he could compete at the Olympics using artificial half-leg blades called Cheetahs that some worried might give him an advantage over runners with legs made of flesh and blood. Neuroscientists are developing more advanced prosthetics that may one day be operated from the brain via fiber optic lines embedded under the skin.

For years, scientists have been manipulating genes in animals to make improvements in neural performance, strength and agility, among other augmentations. Directly altering human DNA using “gene therapy” in humans remains dangerous and fraught with ethical challenges. But it may be possible to develop drugs that alter enzymes and other proteins associated with genes for, say, speed and endurance or dopamine levels in the brain connected to improved neural performance.

Synthetic biologists contend that re-engineering cells and DNA may one day allow us to eliminate diseases; a few believe we will be able to build tailor-made people. Others are convinced that stem cells might one day be used to grow fresh brain, heart or liver cells to augment or improve cells in these and other organs.

Not all enhancements are high-tech or invasive. Neuroscientists are seeing boosts from neuro-feedback and video games designed to teach and develop cognition and from meditation and improvements in diet, exercise and sleep. “We may see a convergence of several of these technologies,” said the neurologist Adam Gazzaley of the University of California at San Francisco. He is developing brain-boosting games with developers and engineers who once worked for Lucas Arts, founded by the “Star Wars” director George Lucas.

Which leads to another question: How far would you go to augment yourself? Would you replace perfectly good legs with artificial ones if they made you faster and stronger? What if a United States Agency for Human Augmentation had approved this and other radical enhancements? Would that persuade you?

Ethical challenges for the coming Age of Enhancement include, besides basic safety questions, the issue of who would get the enhancements, how much they would cost, and who would gain an advantage over others by using them. In a society that is already seeing a widening gap between the very rich and the rest of us, the question of a democracy of equals could face a critical test if the well-off also could afford a physical, genetic or bionic advantage. It also may challenge what it means to be human.

Still, the enhancements are coming, and they will be hard to resist. The real issue is what we do with them once they become irresistible.