It really gets me how your brain completes what you see. The first picture shows what your brain tells you that you see. But in reality, your retina is covered by blood vessels and you see them all the time. Also, there’s a blind spot on your eye that your brain erases and completes for you by averaging the light conditios around it. And your cornea and lens twist the picture so it is both horizontally and vertically flipped.
So the second picture shows what is really projected on your retina.
Seven years ago, Joe Corbo
stared into the eye of a chicken and saw something astonishing. The
color-sensitive cone cells that carpeted the retina (detached from the
fowl, and mounted under a microscope) appeared as polka dots of five
different colors and sizes. But Corbo observed that, unlike the randomly
dispersed cones in human eyes, or the neat rows of cones in the eyes of
many fish, the chicken’s cones had a haphazard and yet remarkably
uniform distribution. The dots’ locations followed no discernible rule,
and yet dots never appeared too close together or too far apart. Each of
the five interspersed sets of cones, and all of them together,
exhibited this same arresting mix of randomness and regularity. Corbo,
who runs a biology lab at Washington University in St. Louis, was
“It’s extremely beautiful just to
look at these patterns,” he said. “We were kind of captured by the
beauty, and had, purely out of curiosity, the desire to understand the
patterns better.” He and his collaborators also hoped to figure out the
patterns’ function, and how they were generated. He didn’t know then
that these same questions were being asked in numerous other contexts,
or that he had found the first biological manifestation of a type of
hidden order that has also turned up all over mathematics and physics.
Quite different from vertebrate eyes, insects possess compound eyes made up of hundreds of tiny repeating facets called ommatidia. Each facet is basically an eye in itself, consisting of a single lens with light-sensitive cells. The facet is fixed in position such that it can only detect light coming from a narrow, single area in space. By combining all of the facets together, insects see a “mosaic” image of the world made up of tiny light and dark dots rather than a sweeping field of view like we see. In this image, a developing fruit fly eye shows the retina (gold) and axons (blue) transmitting light information to the brain (green). Recent research using fruit fly eyes has uncovered novel properties of the retinoblastoma protein, the causative factor in patients with cancer of the same name.
Graphene-Based Artificial Retina Sensor Being Developed
Researchers at Germany’s Technical University of Munich are developing graphene sensors like the ones depicted above to serve as artificial retinas. The atom-thick sheet of linked carbon atoms is being used because it is thin, flexible, stronger than steel, transparent and electrically conductive.
TUM physicists think that all of these characteristics and graphene’s compatibility with the body make it a strong contender to serve as the interface between a retinal prosthetic that converts light to electric impulses and the optic nerve. A graphene-based sensor could help blind people with healthy nerve tissue see, they say.
June 9, 2015 《Tuesday》
Anatomy and physiology (2) exam, quiz, and homework today. Finishing up some homework for today’s class. While studying for the quiz we will be having today. (Exam comes later) a bit overwhelmed. But for now, one step at a time.
Our sense of vision depends on electrical signals travelling from the eye to higher centers in the brain. The image of a mouse retina above shows the path these signals must take. Axons of nerve cells (pictured in yellow) extend through a small opening in the back of the eye (in black) through the optic nerve to higher vision centers. The axons must penetrate another layer of cells known as astrocytes (in blue), which provide nutritional support to the retina. Scientists are currently studying these astrocytes to determine their role in protecting nerve cells in the retina, keeping the connections to the rest of the brain healthy and strong.
Credit: Ward, et al. The Journal of Neuroscience, 2014.