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Diopter Question

This is a discussion on Diopter Question within the ECP Corner forums; According to what I found on the Internet, someone with a sphere of 2.00 means ...


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Old 07-22-2008, 03:09 PM
VAB VAB is offline
Contact Lenses Forum - Masters Degree
  
Join Date: Dec 2007
Posts: 229
Default Diopter Question
According to what I found on the Internet, someone with a sphere of 2.00 means that parallel rays of light will converge at a distance of 1/2 a meter. That brings up a few questions for me.
Isn't the point of contacts or eye glasses supposed to be the focusing light on the retina? If that's true, a half a meter seems way too long. Shouldn't your contact lenses bring parallel light rays together in say, two centimeters instead of 50?
One more question; what does a negative sphere number mean in terms of refracting light?
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Old 08-19-2008, 06:48 PM
Contact Lenses Forum - Bachelors Degree
  
Join Date: Jan 2008
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The only way I can think to explain it would be to give an example.
Say you are nearsighted and need 2 diopters worth of correction. This means that your eyes without correction see best at 0.5 meters (which equals 2 diopters) so a -2.00 lens (which would have a focal length of 0.5 meters) would effectively move the image that you are seeing to 0.5 meters. It obviously doesn't really move the image, it alters the light rays a corresponding amount.
If you look up diopter on wikipedia there is an image of this right above the Aberrations section that shows that a virtual image is formed with the lens. It also has an area that explains the rest of your question.
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