by Bengal Hotdog

Created on: April 27, 2009

As you read this, you are using your central vision. The rest of the room you sit in is seen through your peripheral vision. The difference is simple: central vision is your focal point, and peripheral vision is everything else.

Think of it this way, if you could clearly focus on the whole picture at one time, your brain would be overwhelmed with information.

So how exactly does this work? Put simply, the retina is like the film in a camera. It receives the light, which is absorbed by special cells called photoreceptors and then transformed into nerve impulses. These impulses are then sent to the brain via the optic nerve at the back of each eye.

Central vision is so clear and focused because the light that passes through the eye is mainly concentrated into the center of the retina, on the macula. This is home to the fovea, which is a small area packed densely with only cone cells and is located at the central point of the macula.

Cone cells are one of two types of receptor cells that make up the retina. They receive light and colour, sending clear, bright images to the brain. They are mostly located in the macula, and most densely in the fovea. Cones are a minority on the retina; the rest is made up of rods (The human eye has about four rods to each cone).

Rods are sensitive to low light and a more general, coarse image. They give us the bare bones of the picture and leave the detail up to the cones. You'll notice that your sight is the clearest when you focus on something, and there is less and less detail as you try to concentrate further and further from the focal point. This is due to the density of cones versus rods throughout the retina. The area nearest the fovea is called "near-peripheral". Moving further out there is "mid-peripheral" and furthest is "far-peripheral". The area known as "far-peripheral" is what you use when you see something from the corner of your eye, and does not allow colour vision due to the high percentage of rods compared to cones.

The main difference between peripheral and central vision is seen in acuity. As mentioned earlier, if the entire retina were to process the image in as much detail as the macula, the brain would be swamped with data to register. This is why peripheral vision is so important. It helps the brain run more efficiently, so we can still see the whole picture, but only the tiny focal point in great detail.

Learn more about this author, Bengal Hotdog.
Click here to send this author comments or questions.