Researchers from Johns Hopkins University created a three-dimensional complement of human retinal tissue in the laboratory, which includes functioning photoreceptor cells capable of responding to light, the first step in the process of converting it into visual images.
"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," said study leader M Valeria Canto-Soler, an assistant professor of ophthalmology at the Johns Hopkins University School of Medicine.
Canto-Soler cautioned that photoreceptors are only part of the story in the complex eye-brain process of vision, and her lab has not yet recreated all of the functions of the human eye and its links to the visual cortex of the brain.
"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," she said.
The achievement emerged from experiments with human induced pluripotent stem cells (iPS) and could, eventually, enable genetically engineered retinal cell transplants that halt or even reverse a patient's march toward blindness, the researchers said.
The Johns Hopkins team turned iPS cells into retinal progenitor cells destined to form light-sensitive retinal tissue that lines the back of the eye.
Using a simple, straightforward technique they developed to foster the growth of the retinal progenitors, Canto-Soler and her team saw retinal cells and then tissue grow in their petri dishes, said Xiufeng Zhong, a postdoctoral researcher in Canto-Soler's lab.
The growth, Zhong said, corresponded in timing and duration to retinal development in a human foetus in the womb. Moreover, the photoreceptors were mature enough to develop outer segments, a structure essential for photoreceptors to function.
Retinal tissue is complex, comprising seven major cell types, including six kinds of neurons, which are all organised into specific cell layers that absorb and process light, "see," and transmit those visual signals to the brain for interpretation.
The lab-grown retinas recreate the three-dimensional architecture of the human retina.
When the retinal tissue was at a stage equivalent to 28 weeks of development in the womb, with fairly mature photoreceptors, the researchers tested these mini-retinas to see if the photoreceptors could in fact sense and transform light into visual signals.
They found the lab-grown photoreceptors responded to light the way retinal rods do.
The study was published in the journal Nature Communications.