THE prospect of growing an eye in a laboratory looks more possible after an experiment in which stem cells spontaneously organised themselves into eye-like structures. Japanese researchers watched with surprise as embryonic stem cells from mice formed into an optic cup – a complex, two layered pouch-like structure that becomes the retina of the eye.

The scientists did not push, pull or apply any force to the stem cells, but simply placed them into a special tissue culture on a supportive matrix of proteins.Yoshiki Sasai, of Japan's RIKEN Centre for Developmental Biology in Kobe, said his team's research showed that embryonic stem cells could be converted into complex tissue rather than just single types of cells, such as heart cells or nerve cells. "It is exciting to think we are now well on the way to becoming able to develop organised tissues, which may open new avenues towards applications in regenerative medicine," he said.

Optical cups form in human embryos by about the sixth week of development. Dr Sasai said the study helped solve a century-old mystery, by showing that this happened because the cells had an "inherent ability" to organise themselves into this cup-like structure, without needing signals to do so from other eye tissue, such as the lens.

The research is published in the journal Nature. If it can be repeated with human stem cells, it could lead to the production of complex eye tissue for studying diseases and for testing drugs. It may also, eventually, be possible to grow synthetic retinas – the light-sensitive tissue lining the inner surface of the eye – and obtain cells from it at different stages of development for transplantation, to repair damaged or diseased eyes.

Dr Sasai said this approach might have future applications for treating retinitis pigmentosa, a degenerative condition.