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Medical Forum / General / Vision / September 2008Eye exam - near/far vision
When you get an exam for glasses, does the test give the doctor one number for near vision, and one number for far vision? If so, how does the doctor then decide what to write for Cylinder, if the two are different? > When you get an exam for glasses, does the test give the doctor one > number for near vision, and one number for far vision? > > If so, how does the doctor then decide what to write for Cylinder, if > the two are different? Cylinder is assumed to be exactly the same for near and far. "Cylinder" describes the steepest and flattest meridians. When there is a "+2.00 add," both meridians are changed by +2.00. -MT > > When you get an exam for glasses, does the test give the doctor one > > number for near vision, and one number for far vision? [quoted text clipped - 9 lines] > > -MT When they make bifocals, what do they use for the two different parts? That is, how do you write an Rx for bifocals? From what you say, Cylinder would be the same for near and far. > When they make bifocals, what do they use for the two different parts? > That is, how do you write an Rx for bifocals? From what you say, > Cylinder would be the same for near and far. First consider lenses for distance vision, with cylinder. Then, if the prescription is for bifocals, there's usually just one additional value given for "add." If the "add" is +2.00, it's like pasting on a pair of +2.00 drugstore lenses over the bottom half of the lenses. In other words, the distance prescription should give sphere and cylinder correction to make distant vision "perfect." People with perfect distance vision can correct their near vision with simple drugstore +2.00 glasses. -MT > When they make bifocals, what do they use for the two different parts? > That is, how do you write an Rx for bifocals? From what you say, > Cylinder would be the same for near and far. He is wrong. The Rx has the distance vision (typically measured at 20 ft) and there is an "add" power specification that only applies to the bottom reading area of the lens (so the reading area is the sum of the distance plus the add power). |
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