Tissue engineered replacement retinal tissue lies somewhere in the future, and researchers are making progress towards that goal. Retinal degeneration spurred by the accumulation of metabolic waste products in long-lived retinal cells causes a number of common forms of age-relative blindness, and replacing retinal tissue is one potential approach to repairing these conditions. Here induced pluripotent stem cells are used to generate tissue that somewhat resembles that of a real retina:
Previous studies showed that an early-stage retina, including photoreceptors with primary cilia and parts of the inner segment structure, can be generated in culture from induced human pluripotent stem cells (iPSCs). Now [researchers] demonstrate the ability to grow the most mature retinal tissue from iPSCs yet: the in vitro product was able to develop functional photoreceptor cells. "The major advance here is the ability to make retinal cells that can respond to light and that form into what appears to be remarkably proper orientation."
The miniature human retinal tissue was able to form the outer-segment discs that are essential for light-sensing and contained all seven retinal cell types, including the four types of photoreceptor cells that express opsins, the transmembrane proteins that transfer captured photons into a physiological sensory response to light. While others have also developed systems to study the human retina in the lab, the current study extends these capabilities.
"Outer segments, which are the business end of photoreceptors, have not been previously shown to form from scratch in culture. This study is important as it demonstrated the extent to which we can study the retina in a culture dish. The stem cells could build up the retinal structure almost autonomously. Somehow the cells knew what to do and we just needed to give them time to do it. This was really surprising. The major lessons that [such] stem cell studies are leading us towards is that there are intrinsic instructions within the stem cells themselves to build tissue. We really don't know about these yet, but they are revealing themselves - if we are careful enough to observe them. It makes our jobs as tissue engineers much more doable, if we are working with cells that have these intrinsic emergent properties to build tissues."