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A light-sensitive 'eye-in-a-dish' has been created by scientists using a type of human stem cell.

The three dimensional structure represents a first step towards restoring sight to the blind, say the researchers.

Processes that occur in the womb were copied to create complex retinal tissue in a laboratory petri dish.

A light-sensitive 'eye-in-a-dish' has been created by scientists in Maryland. The three dimensional structure represents a first step towards restoring sight to the blind, say the researchers. Pictured are the photoreceptors (in green) within a 'mini retina' structure (blue) that was created using human stem cells

The retina is the layer of photo-sensitive cells and neurons at the back of the eye that converts light signals into nerve messages transmitted to the brain.

Dr Valeria Canto-Soler, from Johns Hopkins University School of Medicine in Maryland, said: 'We have basically created a miniature human retina in a dish that not only has the architectural organisation of the retina but also has the ability to sense light.

'The work advances opportunities for vision-saving research and may ultimately lead to technologies that restore vision in people with retinal diseases.'

The experiment was conducted using induced pluripotent stem (iPS) cells, adult cells that have been genetically reprogrammed back to embryonic-like state.

Like embryonic stem cells, iPS cells have the potential to develop into virtually any kind of tissue in the body.

The scientists coaxed them to become precursor retinal cells which then developed further into three dimensional structures.

Pictured is a retina coloured in red. 'The work advances opportunities for vision-saving research and may ultimately lead to technologies that restore vision in people with retinal diseases,' said Dr Valeria Canto-Soler from Johns Hopkins University

'We knew that a 3D cellular structure was necessary if we wanted to reproduce functional characteristics of the retina,' said Dr Canto-Soler.

'But when we began this work, we didn't think stem cells would be able to build up a retina almost on their own. In our system, somehow the cells knew what to do.'

At a stage equivalent to 28 weeks of foetal development, the scientists tested the mini-retina by exposing it to pulses of light.

They found that the lab-grown photoreceptors responded to light the same way as they do in the human eye.

Human retinas contain two major photoreceptor cell types, rods and cones. Most are rods, which are sensitive to low light.

Human retinas contain two major photoreceptor cell types, rods and cones. Most are rods, which are sensitive to low light. The petri dish retina was also dominated by rods

The petri dish retina was also dominated by rods.

Dr Canto-Soler said the technique opened up the possibility of generating hundreds of mini-retinas at a time from a person affected by blinding diseases such as retinitis pigmentosa.

These could be used to study the causes of retinal diseases in human tissue, rather than relying on animal models.

Drugs tailored to individual patients could also be tested on the structures.

In the long term, diseased or dead retinal tissue could be replaced by laboratory-grown cells to restore vision, Dr Canto-Soler added.

The experiment was conducted using induced pluripotent stem (iPS) cells, which are adult cells that have been genetically reprogrammed back to embryonic-like state. Like embryonic stem cells (pictured), iPS cells have the potential to develop into virtually any kind of tissue in the body