There is more to vision than just your eyeballs. Sure information and images are collected by the eye and the retina but that info is then transmitted to the brain to be analyzed and interpreted in the visual cortex. You could sort of say your brain tells your eyes what you are seeing, or at least what all that visual data means. How does the info get from your eyes to your brain? Along perhaps the original ‘information superhighway’ well, at least an information superhighway of VISION known as the Visual Pathway.
The Visual Pathway starts in the retina, which is the sight-seeing tissue that lines the inside of each eye. This tissue changes the images you are seeing into chemical signals, then electrical signals. The electrical signals travel along a series of retinal ganglion nerve cells to the brain. You can think of these nerve cells as vision highways. Early along their path in the brain, the highways from each eye meet at a fork in the road. This is known as the optic chiasm and it is shaped like an X because there are two ‘entrances’ to the chiasm where information comes in from each eye and then two exits from the chiasm to the right and left hemispheres of the brain. At this X intersection, some information from the right eye gets transferred to the left side of the brain and some information from the left eye gets transferred to the right side of the brain. So, why the crossover?
Well, we know that images from both eyes (put together in the brain) are essential for binocular vision which gives us our depth perception and 3-D vision. But what triggers the nerve cells from each eye to find their way to the brain during visual development? And what triggers them to swap to different sides of the brain? Recent research may have the beginning of a surprising new answer.
Dr. Lynda Erskine, of the University of Aberdeen and Dr. Christiana Ruhrberg, of the University College London, have conducted research on visual development in mice and shockingly discovered that VEGF164, a molecule usually known for triggering the growth of blood vessels, is actually leading the nerve cells across the chiasm and causing neural cells to cross over to opposite sides of the brain during visual development. They saw that in mice who lacked VEGF 164, there was no crossing of ganglion cells at the optic chiasm. (source 1) Who knew that something we thought only would affect the development of blood vessels in the brain would also be responsible for neuron placement and organization!
The process of vision is so complex and we are learning more about it with each new study. The next time you are playing your favorite 3-D video game or kicking a soccer ball, you can thank your optic chiasm and VEGF 164 for optimizing your vision during your brain’s development, giving you all the info you need to see binocularly! (Just Kidding!)