reading glasses vs power ones

what is the main difference between these 2?

thanks
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anushahannaAsked:
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Anil GolamariConnect With a Mentor Commented:
Although both types of glasses are plus lenses, they are for two different conditions and so the answer is: No, they are not supposed to be the same.

Reading glasses correct for presbyopia, an loss of ability to change the power of the lens inside the eye to focus on near objects. It is normal over age 40. People with presbyopia have normal distance vision and only need glasses to read.

Farsightedness or hyperopia is due to the eye not having enough power to see distance clearly. People under age 40 with hyperopia can change the power of their lens to clear the distance but it may cause double vision, headache and eye strain. They wear their glasses full time to relieve the strain.

When hyperopes turn age 40, they will also lose the ability to change focus to see up close and will need bifocals.

http://www.questionhub.com/YahooAnswers/20081018195629AAyA8F0
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Brian PringleConnect With a Mentor Systems Analyst II, SCM, ERPCommented:
Reading glasses have a positive correction number, while power glasses have negative correction numbers.

The difference is the way that the glass is curved.  Reading glasses are convex, which means that they are thinner at the edges and get thicker towards the middle of the lens.  The power lenses are concave, which means they are thicker at the edges and get thinner towards the middle.

The reading glasses are used when it is difficult to look at items up close.   The power glasses are used when it is difficult to view items far away.
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harfangConnect With a Mentor Commented:
Glasses worn for hyperopia and presbyopia are exactly the same, from an optical point of view. Often reading glasses have a half-moon shape making it easy to peek over the brim, but the lenses are exactly the same, convex in shape and positive in power.

Lenses for myopia are concave, negative in power, and lenses for astigmatism have a different correction in perpendicular directions, for example -2 vertically and -1 horizontally. If one direction has zero correction, they are called cylindrical lenses.

(°v°)
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anushahannaAuthor Commented:
Thanks for the info.
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anushahannaAuthor Commented:
>>lenses for astigmatism have a different correction in perpendicular directions, for example -2 vertically and -1 horizontally

is this in the same context as myopia? in the above example, does it mean one eye has diff power need than the other?
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ozoConnect With a Mentor Commented:
> does it mean one eye has diff power need than the other?
no, it means one eye has diff power need in different planes
http://en.wikipedia.org/wiki/Astigmatism
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anushahannaAuthor Commented:
Thanks for the helpful info on Astigmatism.
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anushahannaAuthor Commented:
so, let me summarize; can you see if got it right:

1.Astigmatism can come along with myopia but not necessarily.
2.hyperopia and presbyopia have the same solution- helps the folks to see things clearly closely.
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