Saturday, March 08, 2008/10:32 PM
How do we see
HOW DO WE SEE????
Everyone knows that the eyes are the organs of vision (Don't believe me? Close your eyes, do you see the computer screen now?).
But actually, our eyes do not SEE the objects, they are just the MEDIUM through which we see.
We are able to see because of light, without it, we cannot see.
***
In order for us to see clearly, the right amount of light should enter the eye (e.g. less light must enter the eye in bright light).
The size of the pupil determines how much light enters the eye. And the size of pupil is in turn controlled by two sets of involutary muscles in the iris---CIRCULAR MUSCLES AND RADIAL MUSCLES.
Circular muscles are arranged in circles round the pupil, while the radial muscles are arranged radially. They are also called antagonistic muscles because when one set contracts, the other set relaxes and vice versa.
But actually, our eyes do not SEE the objects, they are just the MEDIUM through which we see.
We are able to see because of light, without it, we cannot see.
Our eyes respond to changes in light and enable us to see
- by controlling the amount of light entering the eye, and
- by focusing light reflected from objects onto the retina.
***
In order for us to see clearly, the right amount of light should enter the eye (e.g. less light must enter the eye in bright light).
The size of the pupil determines how much light enters the eye. And the size of pupil is in turn controlled by two sets of involutary muscles in the iris---CIRCULAR MUSCLES AND RADIAL MUSCLES.
Circular muscles are arranged in circles round the pupil, while the radial muscles are arranged radially. They are also called antagonistic muscles because when one set contracts, the other set relaxes and vice versa.
***
Light from an object is reflected in all directions.
Some of it enters the front of the our eye - the transparent cornea - and is refracted as it meets its curved surface. It then goes through the pupil, and enters the lens, and finally reached the retina.
1) The cornea’s refractive power bends the light rays in such a way that they pass freely through the pupil.
2) The iris works like a shutter in a camera. It has the ability to enlarge and shrink, depending on how much light the environment is sending into the eye.
3) The light rays then strike the lens, which works much like the lens in a camera – shortening and lengthening its width in order to focus light rays properly.
5) Finally, the light rays land and come to a sharp focusing point on the retina, which mainly functions like the film in a camera. It is responsible for capturing all of the light rays, processing them into light impulses through millions of tiny nerve endings, then sending these light impulses through over a million nerve fibers to the optic nerve.
Tidbit: Retina contains light-sensitive cells / photoreceptors, which consist of rods and cones. Cone enable us to see colours in bright light while rods enable us to see in black and white in dim light. The photoreceptors are connected to the nerve-endings from the optic nerve.
6) The optic nerve is like an extension of the brain. It is a bundled cord of more than a million nerve fibers. The nerve impulses travel are transmitted by the nerve fiber to the brain, where they are interpreted as an image.
Some of it enters the front of the our eye - the transparent cornea - and is refracted as it meets its curved surface. It then goes through the pupil, and enters the lens, and finally reached the retina.
1) The cornea’s refractive power bends the light rays in such a way that they pass freely through the pupil.
2) The iris works like a shutter in a camera. It has the ability to enlarge and shrink, depending on how much light the environment is sending into the eye.
3) The light rays then strike the lens, which works much like the lens in a camera – shortening and lengthening its width in order to focus light rays properly.
4) The light rays are refracted by the lens and pass through the vitreous humor.
5) Finally, the light rays land and come to a sharp focusing point on the retina, which mainly functions like the film in a camera. It is responsible for capturing all of the light rays, processing them into light impulses through millions of tiny nerve endings, then sending these light impulses through over a million nerve fibers to the optic nerve.
Tidbit: Retina contains light-sensitive cells / photoreceptors, which consist of rods and cones. Cone enable us to see colours in bright light while rods enable us to see in black and white in dim light. The photoreceptors are connected to the nerve-endings from the optic nerve.
6) The optic nerve is like an extension of the brain. It is a bundled cord of more than a million nerve fibers. The nerve impulses travel are transmitted by the nerve fiber to the brain, where they are interpreted as an image.
***
Now, let's watch a video to learn about how the eyes focus.
Enjoy! (:
Now, let's watch a video to learn about how the eyes focus.
Enjoy! (: