In another step towards reversing degenerative vision loss, scientists said they had coaxed stem cells into growing into a tiny, light-sensing retina in a lab dish.
The study is an important technical feat in using reprogrammed cells, whose discovery in 2006 has unleashed huge interest, they said.
"We have basically created a miniature human retina in a dish that not only has the architectural organization of the retina but also has the ability to sense light," Valeria Canto-Soler of Johns Hopkins University School of Medicine, Baltimore, said Tuesday.
The work is the latest advance towards the goal of creating transplant cells that reverse damage to the retina, the light-capturing surface on the back of the eyeball.
Stem cells are infant cells that develop, or differentiate, into the various tissues of the body.
Until 2006, the big focus was on stem cells culled from early-stage embryos, which are highly versatile but also ethically controversial.
That changed with the discovery in Japan of so-called human induced pluripotent stem cells (iPS cells), which are adult cells that have been reprogrammed to return to a youthful, pre-differentiated state.
The latest research marshals the iPS into the right architecture for the retina, ordering the complex layers of specific photoreceptor cells which absorb and process light.
More work is needed, though, to understand how these cells transmit signals to the brain.
Experiments in a lab dish, however remarkable, still need to be validated in tests on humans before they can be incorporated into medical practice.
"Is our lab retina capable of producing a visual signal that the brain can interpret into an image? Probably not, but this is a good start," Canto-Solder said in a press release.
Japan last year gave the green light for the world's first trial on humans of iPS cells for age-related macular degeneration (AMD), which causes blindness in older people. Six patients with AMD will be recruited in a four-year trial.