The cell biologists, from Johns Hopkins University, managed to grow human retina tissue from scratch as the starting point for their experiments in understanding the cells that allow us to see in color are formed. Using this knowledge the scientists hope they will be able to form therapies for eye diseases like color blindness or macular degeneration.
According to one of the researchers, Dr. Robert Johnston: “Everything we examine looks like a normal developing eye, just growing in a dish. You have a model system that you can manipulate without studying humans directly.”
This model has been put to work to help determine how most people can differentiate the colors of red, green and blue, a process that provides the basis for seeing in color. These colors are the three cone photoreceptors in the retina of the human eye. Cone cells are densely packed in the fovea centralis, a 0.3 millimeter diameter area composed of very thin, densely packed cones. There are some six to seven million cones in a human eye. Different people different response curves and so we respond to variation in color in different ways.
It is partly due to this last point that the lab-grown retinas were required. Previous work has been performed on fish and rodents; however, these creatures are not capable of the same dynamic daytime and color vision of humans.
The retinas took several months to grow. During the developments process, the researchers noted that blue-detecting cells materialized first; this was followed by the red- and then the green-detecting ones. The process that controlled this was the release of thyroid hormone, dictating whether the cells became blue or red and green. This could mean that babies with lowered thyroid hormone levels could be more likely to develop color blindness.
As well as assisting with eye research, the development can also assist wit other research, as it has established the protocol for producing laboratory-created “organoids”, which can be used as the model to study other facets of human development at the cellular level.
The new research has been published in the journal Science. The research paper is titled “Thyroid hormone signaling specifies cone subtypes in human retinal organoids.”