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The Science of Seeing: Unraveling Human Vision & Primate Color Perception

Posted by Ilena Di Toro | Posted on January 9, 2024

Call us biased, but we think vision is very cool. The images that our eye sees are encoded as visual information in the brain and the images enable us to see, navigate and learn. No wonder the eyes are considered the front of the brain, and biomedical research is uncovering different aspects of vision that make human vision unique. One research project at New York University Langone Health studied lab-grown “mini-corneas” and another at the University of Washington School of Medicine studied the differences in the way people and primates see color.

Starting with at New York University Langone Health, a research team designed corneal organoids resembling a human cornea. The hope is that these lab-grown corneas can be used to study corneal disease and eventually used as cell therapies to treat this disease.

This is the first study of its kind to examine human corneal organoids at the single-cell stage. To conduct this research, scientist constructed the organoid from stem cells with specific nutrient adjustments, so that the cell types develop and organize themselves in three dimensions. This structure mimics the original structure and function of corneal tissues in the eye better than other methods. What researchers found from reading the organoid’s genetic code is that they perform just as actual corneas developing in the womb.

The scientists used an approach for this study known as single-cell RNA sequencing to identify cell-specific genes activated in both lab made corneal organoids and corneas from adult human cadavers. The RNA sequencing revealed that the adult corneas consisted of an outer layer of epithelial cells and a middle layer of stromal cells. In contrast, the organoids in the study had a large quantity of cells in all three layers. In fact, one-third to one-fourth of developing cells in the organoid had epithelial cells and the activated gene signature of the organoid was similar to a developing immature cornea.

The advantage to using these organoids is that they allow researchers to examine gene expression as it is developing. They also provide a way to screen for therapies for genetic eye diseases at a cost lower than that of the mouse model.

Now for the coolest thing about vision, namely seeing in color. Human can see approximately one million colors. What about animals, specifically monkeys? Can they see in color? Which ones and how many?

Scientists at the University of Washington School of Medicine led an international project that had collaborators from the Medical University of Vienna, Austria, the University of Sydney, Australia and Save Sight Institute to learn more about human vision.

Researchers looked at the retinas of humans and two types of monkeys, Old World Macaques and New World marmosets. Through the use of a fine scale microscopic reconstruction method, they wanted to learn if the neural wiring responsible for color vision in specific areas is preserved across these species, despite each following a different evolutionary pathway.

They focused on the cone cells, which detect light waves, in the fovea of the retina. The fovea is filled with cone cells and is responsible for the sharp vision needed to see details such as words on a page and for color vision. The cone cells have three sensitivities: short, medium and long wavelengths. Color information comes from neural circuits that process information across different cone types.

Scientists found that the blue sensitive cone circuit found in humans is absent in marmosets and it is different from the circuit seen in macaque monkeys. They speculate that the differences among mammalian visual circuitry might be shaped by adaptation to habitat. For example, since marmosets live in trees and humans on land, specific color visual circuitry might offer advantages such as spotting ripe fruit in trees. Of course, more studies need to be done in order to learn how evolution has fashioned the nervous system in terms of perception and behavior.

Medical research is uncovering more information about the ins and outs of human vision. Still, will this help the next time there an Internet challenge that asks what color a specific item is?


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