Chapter 6 - Correcting and Extending Human VisionThis is a featured page

Chapter 6 - Correcting and Extending Human Vision - Surrey Connect Science 8 WikinotesChapter 6 - Correcting and Extending Human Vision - Surrey Connect Science 8 WikinotesChapter 6 - Correcting and Extending Human Vision - Surrey Connect Science 8 WikinotesUnit 6 - Correcting and Extending Human Vision - Surrey Connect Science 8 Wikinotes

The structure of the Human Eye -

Consists of the Iris, the pupil, the sclera, the cornea, the optic nerve, the retina, the focal point, muscles and lens.eye With light that enters through the pupil first being refracted by the

How We See

Looking at things seems so effortless to us, even though it is one of the most complex things to do with the human body.

The Cornea-Lens-Retina System

The human eye employs a system known as the cornea-lens-retina system. It is so named because the cornea, and lens refract the light entering the eye so that it is focused on a certain part of the retina called the macula. The cornea first refracts the light into the the pupil. The iris muscle controls how much light gets through the pupil. The lens does the rest of the refracting and focuses the image on the retina.

Rod Cells

Once light is focused on the retina there are two types of cells that help turn it into an image. The first is the rod cell which helps to eye to detect motion. Rod cells help us see in low light conditions.

Cone Cells

Cone cells are responsible for detecting colour. There are three types of cone cells each enabling us to see different colours, red, green and blue. Combinations of these colours make up all the colours of the rainbow.

Vision Problems

Some people have certain problems with their eyes that affect the way they see. Two of the most common problems that affect men and women is near sightedness, and far sightedness. Near sightedness is caused when a persons lens converges light rays in a way that makes them form an image in front of the retina, making the image people see from a distant object fuzzy. Far sightedness is caused when the lens refracts the light rays so the image is formed behind the retina, so light from near objects are blurred. There is also a vision problem called astigmatism, in which the cornea is in a distorted shape, making light to focus on more than one point on the retina, resulting in blurred vision. Blindness is a very severe vision problem that comes in different forms of severity. Some people can perceive a small part of the whole scene, while other people can only see the outer edges, and in some cases, people can not see at all. Certain forms of blindness can be fixed, but 20 percent of all people with blindness cannot gain or regain their vision.

Correcting Focus Problems

There are a couple of ways to correct vision problems. One way for people with near sightedness or far sightedness is with glasses or contacts, as they refract the light properly onto the retina, or they can get laser eye surgery to adjust the lens to refract light properly. Someone with Astigmatism can get contacts or glasses, but the preferred option is laser eye surgery.
keratoprostheses: these are artificial corneas, this technology is still in development. Most of these are just plastic inserts though some are made frombiocompatible synthetic materials.

Different Types of Blindness

Snow blindness is a very awful and painful condition of temporary partial or even complete wich is caused by overexposure to the glare of sunlight, its treatment includes resting the eye in a dark room for a couple of days untill the inflammation decreases. Night blindness is another type of blindness in which it is difficult or even impossible to see in dim light and this type is caused by rod cells losing their ability to respond to light. Colour Blindnes is another condition in which the person that is effected could only see in shades of grey, and happens in about a person in every 40 000.


Telescopes are devices that use lenses or mirrors (or a combination of the two) to see objects far away.

- Refracting telescopes.
Inside refracting telescopes there are two convex lenses, one that's small, and one that's big. The big lens is at the front of the telescope, the part that you point at things that you want to look at, and the small one is positioned directly in front of the eyepeice. When you point the end of the telecope at a far away object, the large lens collects large amounts of light that your eye cannot. The lens makes the light converge. The light converges, then begins to spread apart until it comes to the second lens, which converges the light once again onto the eye of the person using the telescope. A problem with bigger refracting telescopes is that finding a piece of glass that is very big and of high quality can be very hard and expensive, and the glass in the telescope can sag under its own weight, distorting the image. Also, even when the highest quality of glass is used, the glass still absorbs some of the light that comes into it. For these reasons, most large telescopes are reflecting telescopes.

- Reflecting telescope.
Reflecting telescopes are more complex and confusing than refracting telescopes. There are two mirrors and one lens inside reflecting telescopes, a concave mirror, a plane mirror and a convex lens. The concave mirror is positioned at the back of the telescope and it is very big, the plane mirror is positioned about 1/5th away from the front of the telescope, it is positioned in the middle of the telescope. It is very small. The lens is positioned in front of the eyepiece, directly across from the plane mirror. When you point the front of the telescope at what you want to look at, the light enters the microscope. When it hits the back of the microscope, a concave mirror makes the light slowly converge and travel back towards the front of the telescope. Just before the light is about to converge, it hits the plane mirror, which is positioned on an angle. This mirror directs the light towards the eyepeice lens, which converges the light even more so that the person looking into the telescope can see it.

- Hubble space telescope
The Hubble Space Telescope was launched in 1990. It is a reflecting telescope that is contained inside a satellite. This satellite travels around space taking pictures of galaxies and planets with its telescope and sending the pictures back to earth. The Hubble Space Telescope produces very sharp looking pictures that telescopes positioned here on earth are not able to produce. The reason this telescope produces such good pictures is because the pictures it takes are not blurred by earth's atmosphere like the pictures that we take of space on earth. For this reason, the Hubble Telescope has produced some of the highest quality pictures of outer space in existance.

I learned a lot of different things about the eye. like what parts go where and everything. The sclera, cornea, pupil, and iris. they are all very interesting. I also learned about the blind spot in the eye. Everyone has one. My family and I were very interested in it.

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