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Vision depends on light, either from the sun or from an artificial source such as a light bulb. Light reflects off objects and enters your eyes through a clear covering, or CORNEA, over the front of the eye. The cornea does most of the focusing of light onto the retina. Behind the cornea is the LENS which does some of the focusing and enables the eye to vary its focus. Images are formed the back of the eye, on the RETINA. The retina turns the picture into tiny electric impulses that are sent by way of the OPTIC NERVE to the brain, where seeing actually occurs. The most light-sensitive point of the retina, near its center, where the sharpest vision is achieved, is called the MACULA. This part of the retina governs CENTRAL VISION, which is what you see when you look straight at an object, such as a word on a page. PERIPHERAL (SIDE) VISION is what you see of the area surrounding the object at which you are looking. With you peripheral vision you can tell if the word is at the beginning or end of the line or at the top or bottom of the page. Your peripheral vision also tells you when someone enters the room. Peripheral vision lets you walk or drive without bumping into or stumbling over objects. Central vision sometimes is called "seeing or reading" vision and peripheral vision is called "traveling" vision. Let us look at a scene and what happens with certain types of blindness. Only a person who is blind or visually impaired really knows what it is like, but these images may help you understand more about the main types of visual impairment.
This is the scene.
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The next two pictures depict MACULAR DEGENERATION. Remember that the Macula is the center part of the retina that helps us to see what is directly ahead. The cause of Macular Degeneration is unknown and it is mostly seen in people over 50. There is little or no treatment available for this condition but it does not lead to total blindness--only the loss of central vision.
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Here is another view of Macular Degeneration Would you feel comfortable crossing the street by yourself with Macular Degeneration? How about reading a book or watching TV?
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This is how the scene might look if your retina was detached. A retinal detachment can be brought about by a number of different causes: an injury to the eye or face (as happened to the boxer Sugar Ray Leonard), an eye disease (such as Diabetic Retinopathy), or a family history of retinal detachments. Wherever the retina detaches, the person experiences a blind spot. In many cases the retina can be reattached with laser treatment or surgery. In more severe cases or where another eye condition may be causing the detachment, the retina may not be reattached successfully, leading to partial or total vision loss, as in the nest picture.
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Glaucoma is a condition caused by an abnormally high pressure of the fluid in the eye. It usually does not cause pain, so people are unaware that they have it. If caught early enough by an ophthalmologist or optometrist it can be treated successfully without causing any loss of vision. If no treated early enough, the person would lose peripheral vision very gradually until all vision is eventually gone. There is also a form of Glaucoma that is congenital (from birth). This form also leads to vision loss that eventually ends in total blindness.
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As peripheral; vision shrinks, it leads to tunnel vision. Can you tell what part of the scene you are seeing? If you saw like this, would you feel comfortable crossing the street by yourself? Do you think a dog could help you? Could you read a book or watch TV?
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If the lens of the eye grows cloudy, the result is cataracts. This next picture shows how the scene would look if you had cataracts. Cataracts are most often caused by the aging process but can also occur at birth or be caused by other diseases of the eye such as Diabetic Retinopathy. Cataracts are very successfully treated today with a surgical procedure that removes the cataract and implants an artificial lens in its place. People with other eye conditions who also have cataracts sometimes cannot have them removed because of the danger of further vision loss due to the other conditions.
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