katyzzzVision and Working
August 3rd 2006 01:13
Vision and Working :
It’s no accident that the main function of the sun at the center of our solar system is to provide light. Light is what drives life. It’s hard to imagine our world and life without it.
The sensing of light by living things is almost universal. Plants use light through photosynthesis to grow. Animals use light to hunt their prey or to sense and escape from predators. Some say that it is the development of stereoscopic vision, along with the development of the large human brain and the freeing of hands from locomotion, that have allowed humans to evolve to such a high level.
Basic Anatomy :
Although small in size, the eye is a very complex organ. The eye is approximately 1 inch (2.54 cm) wide, 1 inch deep and 0.9 inches (2.3 cm) tall.
The tough, outermost layer of the eye is called the sclera. It maintains the shape of the eye. The front sixth of this layer is clear and is called the cornea. All light must first pass through the cornea when it enters the eye. Attached to the sclera are the muscles that move the eye, called the extraocular muscles.
The choroid (or uveal tract) is the second layer of the eye. It contains the blood vessels that supply blood to structures of the eye. The front part of the choroid contains two structures:
The ciliary body - The ciliary body is a muscular area that is attached to the lens. It contracts and relaxes to control the size of the lens for focusing.
The iris - The iris is the colored part of the eye. The color of the iris is determined by the color of the connective tissue and pigment cells. Less pigment makes the eyes blue; more pigment makes the eyes brown. The iris is an adjustable diaphragm around an opening called the pupil.
Normal Vision :
Vision or visual acuity is tested by reading a Snellen eye chart at a distance of 20 feet. By looking at lots of people, eye doctors have decided what a "normal" human being should be able to see when standing 20 feet away from an eye chart. If you have 20/20 vision, it means that when you stand 20 feet away from the chart you can see what a "normal" human being can see. (In metric, the standard is 6 meters and it's called 6/6 vision). In other words, if you have 20/20 vision your vision is "normal" -- a majority of people in the population can see what you can see at 20 feet.
If you have 20/40 vision, it means that when you stand 20 feet away from the chart you can only see what a normal human can see when standing 40 feet from the chart. That is, if there is a "normal" person standing 40 feet away from the chart, and you are standing only 20 feet away from the chart, you and the normal person can see the same detail. 20/100 means that when you stand 20 feet from the chart you can only see what a normal person standing 100 feet away can see. 20/200 is the cutoff for legal blindness in the United States.
Astigmatism :
Astigmatism is an uneven curvature of the cornea and causes a distortion in vision. To correct this, a lens is shaped to correct the unevenness.
Depth Perception :
The eye uses three methods to determine distance:
The size a known object has on your retina - If you have knowledge of the size of an object from previous experience, then your brain can gauge the distance based on the size of the object on the retina.
Moving parallax - When you move your head from side to side, objects that are close to you move rapidly across your retina. However, objects that are far away move very little. In this way, your brain can tell roughly how far something is from you.
Stereo vision - Each eye receives a different image of an object on its retina because each eye is about 2 inches apart. This is especially true when an object is close to your eyes. This is less useful when objects are far away because the images on the retina become more identical the farther they are from your eyes.
Blindness :
Legal blindness is usually defined as visual acuity less than 20/200 with corrective lenses. Now that you have learned some anatomy of the eye and how it functions, it becomes easier to understand how the following conditions can lead to blindness:
Cataracts - This is a cloudiness in the lens that blocks light from reaching the retina. It becomes more common as we age, but babies can be born with a cataract. As it worsens, it can require surgery to remove the lens and place an intraocular lens.
Glaucoma - If the aqueous humor does not drain out correctly, then pressure builds up in the eye. This causes the cells and nerve fibers in the back of the eye to die. This can be treated with medications and surgery.
It’s no accident that the main function of the sun at the center of our solar system is to provide light. Light is what drives life. It’s hard to imagine our world and life without it.
The sensing of light by living things is almost universal. Plants use light through photosynthesis to grow. Animals use light to hunt their prey or to sense and escape from predators. Some say that it is the development of stereoscopic vision, along with the development of the large human brain and the freeing of hands from locomotion, that have allowed humans to evolve to such a high level.
Basic Anatomy :
Although small in size, the eye is a very complex organ. The eye is approximately 1 inch (2.54 cm) wide, 1 inch deep and 0.9 inches (2.3 cm) tall.
The tough, outermost layer of the eye is called the sclera. It maintains the shape of the eye. The front sixth of this layer is clear and is called the cornea. All light must first pass through the cornea when it enters the eye. Attached to the sclera are the muscles that move the eye, called the extraocular muscles.
The choroid (or uveal tract) is the second layer of the eye. It contains the blood vessels that supply blood to structures of the eye. The front part of the choroid contains two structures:
The ciliary body - The ciliary body is a muscular area that is attached to the lens. It contracts and relaxes to control the size of the lens for focusing.
The iris - The iris is the colored part of the eye. The color of the iris is determined by the color of the connective tissue and pigment cells. Less pigment makes the eyes blue; more pigment makes the eyes brown. The iris is an adjustable diaphragm around an opening called the pupil.
Normal Vision :
Vision or visual acuity is tested by reading a Snellen eye chart at a distance of 20 feet. By looking at lots of people, eye doctors have decided what a "normal" human being should be able to see when standing 20 feet away from an eye chart. If you have 20/20 vision, it means that when you stand 20 feet away from the chart you can see what a "normal" human being can see. (In metric, the standard is 6 meters and it's called 6/6 vision). In other words, if you have 20/20 vision your vision is "normal" -- a majority of people in the population can see what you can see at 20 feet.
If you have 20/40 vision, it means that when you stand 20 feet away from the chart you can only see what a normal human can see when standing 40 feet from the chart. That is, if there is a "normal" person standing 40 feet away from the chart, and you are standing only 20 feet away from the chart, you and the normal person can see the same detail. 20/100 means that when you stand 20 feet from the chart you can only see what a normal person standing 100 feet away can see. 20/200 is the cutoff for legal blindness in the United States.
Astigmatism :
Astigmatism is an uneven curvature of the cornea and causes a distortion in vision. To correct this, a lens is shaped to correct the unevenness.
Depth Perception :
The eye uses three methods to determine distance:
The size a known object has on your retina - If you have knowledge of the size of an object from previous experience, then your brain can gauge the distance based on the size of the object on the retina.
Moving parallax - When you move your head from side to side, objects that are close to you move rapidly across your retina. However, objects that are far away move very little. In this way, your brain can tell roughly how far something is from you.
Stereo vision - Each eye receives a different image of an object on its retina because each eye is about 2 inches apart. This is especially true when an object is close to your eyes. This is less useful when objects are far away because the images on the retina become more identical the farther they are from your eyes.
Blindness :
Legal blindness is usually defined as visual acuity less than 20/200 with corrective lenses. Now that you have learned some anatomy of the eye and how it functions, it becomes easier to understand how the following conditions can lead to blindness:
Cataracts - This is a cloudiness in the lens that blocks light from reaching the retina. It becomes more common as we age, but babies can be born with a cataract. As it worsens, it can require surgery to remove the lens and place an intraocular lens.
The Eye
Glaucoma - If the aqueous humor does not drain out correctly, then pressure builds up in the eye. This causes the cells and nerve fibers in the back of the eye to die. This can be treated with medications and surgery.
| 7 |
| Vote |
Subscribe to this blog
Address: 3/19 Wyuna Road, Caulfield North, Victoria, 3161
Send An Email
Tel: 95714294
