The human eye can seem like quite a mystery. For such a small part of the body, it accomplishes an incredible task. But how?
Vision cannot occur without light. When light reflects off an object, it enters the eye through the cornea, which is the transparent outer covering of the eye. All of the rays that pass through the cornea are bent to pass through the pupil, which is the small circle surrounded by the colored portion of the eye called the iris. The iris has an ability to open and close in order to make the pupil bigger or smaller. The bigger the pupil, the more light can shine into the eye. This comes in handy in darker rooms when the eye needs as much light as possible to generate clear vision.
After passing through the pupil, light rays then head through the lens, which bends the rays even more so they can be projected onto the retina. The lens also focuses the light, similar to the way a lens of a camera does. The retina, located at the back of the eye, is a thin layer of tissue that contains millions and millions of microscopic nerve cells responsible for sensing light. Think of the retina as a movie screen with multiple working parts.
Six main components work together to help the retina function. Blood vessels bring nutrients to the retina’s nerve cells, keeping everything alive. The macula is the bullseye that sits at the center of the retina with photoreceptors that convert light into electrochemical signals. Each of the other six parts play critical roles in keeping the eye functioning properly.
The next step is what makes vision available for human use, but it doesn’t really involve the eye at all. Once the photoreceptors in the retina convert light into electrochemical signals, those signals travel along nerve fibers to the optic nerve, a bundle of nerves that send signals to the visual hub in the brain. The brain interprets all of the electrochemical signals as images, and sight is created.