Scientists restore sight in blind mice

Scientists have taken a crucial step towards restoring the sight of people suffering from degenerative eye diseases like retinitis pigmentosa and age-related macular degeneration.

Writing in the journal Nature the team, based at UCL's Institute of Opthalmology, show that transplanting light-sensitive photoreceptors into the eyes of visually impaired mice can restore their vision.

"This is a landmark study" says Professor Robin Ali who led the research. "We've shown for the first time that transplanted photoreceptors can integrate successfully with the retinal circuitry, making synaptic connections, and truly improving vision".

The research involved transplanting immature, or progenitor, rod photoreceptors into the lining of the retina in blind adult mice. Rod cells are especially important for seeing in the dark as they are extremely sensitive to low levels of light. After about four to six weeks the transplanted cells appeared to have integrated well, and formed the connections needed to transmit visual information to the brain.

So well in fact that the mice with newly transplanted rod cells were able to use visual cues to find a hidden platform in a dimly-lit maze almost as quickly as healthy controls.

The loss of light-sensitive photoreceptors is the cause of blindness in many human eye diseases, but there's a long way to go before the technique could be applied in a clinical setting.

"It's a proof of concept" says professor Ali. "What's exciting is that it demonstrates the feasibility of this approach. But it's important to stress we're still a long way from a clinical application in humans".

One problem that remains to be overcome will be sourcing progenitor photoreceptors for transplant in humans. The cells used in this experiment were taken from neo-natal mice - not something that would ever be countenanced in humans. The UCL team are already looking at how they might get round the problem by stimulating embryonic stem cells to differentiate into photoreceptors.

Once they've cracked that all that remains is to repeat the whole process for cone cells - the other type of light sensitive photoreceptor cell lining the retina.

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