Harvard scientists announced this week that they have successfully used stem cells to restore vision in mice with the rodent equivalent of macular degeneration, a leading cause of blindess in humans. The disease is characterised by the progressive loss of light-sensitive cells from the central part of the retina - the macula - which is responsible for high-acuity vision. Damage to this region leaves an affected person unable to see what is directly in front of them, meaning that they have difficulty reading, watching television, or even seeing peoples' faces. Wondering whether stem cells could help to repair the damage and restore sight, the Harvard scientists transplanted stem cells collected from mice engineered to glow green, into the eyes of a second group of mice with retinal disease. The glowing green colour made the transplanted cells easy to follow, and the researchers found that they made their way to damaged regions of the retina and turned into new retinal cells. At the same time, the rate of damage to the existing retinal tissue also appeared to slow down, leading the scientists to suggest that perhaps the transplanted cells were secreting protective growth factors capable of keeping the diseased retina alive. Next, the researchers tested the transplanted mice to find out whether they could see any better than control mice not given any stem cells. This was done by shining progressively dimmer lights at them. Normally-sighted mice are photophobic and stop what they are doing when a light shines their way. Encouragingly, the transplanted mice continued to respond in this way, even at the dimmest light levels, but the control (untransplanted mice) did not showing that the transplanted mice had better light perception compared with their control counterparts. The researchers are optimistic that this approach might also work in humans and are now testing the technique in pigs which have bigger eyes, more like people.


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