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how to tell your eyesight from your prescription?

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You just finished your annual eye exam and with prescription in hand, you’re thinking about what kind of cool eyeglasses to try. Have you ever looked at all those numbers and letters and wondered what exactly do they mean? Whether you’re a longtime glasses wearer or a newbie, knowing how to decipher your prescription will give you a better understanding of what the eyeglass prescription could say about your vision and overall health.

Your eyeglass prescription is typically written in a grid like the one below, using a combination of terms, abbreviations, and numbers. Usually you’ll see these abbreviations along the left side:

O.D. stands for oculus dexter, meaning right eye.
O.S. stands for oculus sinister, meaning left eye.
O.U. stands for and oculus uterque, meaning both eyes.

Then along the top, you may see this lingo. These abbreviations reflect the measurements of specific aspects of your vision, and can be pretty confusing at first.

SPH(or Sphere) indicates the eyeglass prescription power, or how strong your lenses need to be to correct your vision. For an indicator of how much magnifying power is needed in a bifocal or progressive lens to correct your vision problems, look for ADD.

CYL (or Cylinder) indicates astigmatism, a condition where the cornea is irregularly shaped causing blurred or distorted vision. It also tells the lens strength needed to fix it. 

AXIS describes the degree and direction of your astigmatism. 

ADD is added magnifying power in the lower part of a multi-focal lens. It’s used to correct presbyopia which is the inability to focus on close objects.

Eyeglass Prescription Chart
Your glasses prescription includes a number for every aspect of your vision that needs correction. When learning how to interpret your prescription, keep in mind that usually the further from zero the numbers are, the more correction you need.

A plus or minus sign in front of your glasses prescription number is shorthand for
near or farsightedness.
+ means you’re farsighted or have trouble seeing things close up.
- means you’re nearsighted, or struggle with seeing far away.

Single and multi-focal eyeglass prescriptions will look different.

If your vision correction is single vision, that means your lens power corrects for nearsighted or farsighted, but not both. The ADD column (which stands for additional magnifying in a multi-focal Rx) is blank in the sample Rx above. If you’ve got an eyeglass prescription for bifocal or multi-focal/progressives, your lens power corrects for near, far, and sometimes intermediate range vision. You’ll have a number in the ADD column.

No matter what your eyesight numbers are, or whatever kind of vision correction you need, it’s good to have your eyes examined about once a year to make sure your prescription for eyeglasses or contact lenses is up to date.

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asked Feb 12, 2017 in Health by smyadmin
reshown Feb 12, 2017 by smyadmin

1 Answer

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When you look at your prescription for eyeglasses, you will see numbers listed under the headings of OS and OD. They are Latin abbreviations: OS (oculus sinister) means the left eye and OD (oculus dextrus) means the right eye. Occasionally, you will see a notation for OU, which means something involving both eyes. In general, the further away from zero the number on your prescription, the worse your eyesight and the more vision correction you need. A plus sign in front of the number means you are farsighted and a minus sign means you are nearsighted. These numbers represent diopters, the unit used to measure the correction, or focusing power, of the lens your eye requires. Diopter is often abbreviated "D."

For example, if your prescription says -1.00, you have one diopter of nearsightedness. This is a fairly mild amount of nearsightedness. If you are -4.25, that means you have 4 and 1/4 diopters of nearsightedness. This is more nearsighted than -1.00, and requires stronger (thicker) lenses. Similarly, +1.00 would be a small amount of farsightedness and +5 would be more.

For people who have astigmatism, there will be three numbers in your prescription. The general form for writing these numbers is S x C x Axis

The S refers to the "spherical" portion of the prescription, which is the degree of nearsightedness or farsightedness discussed above.

The C refers to the "cylinder" or astigmatism, and can be a negative or a positive number. It measures in diopters the degree of astigmatism that you have. The bigger this number, the more astigmatism you have. Astigmatism most often is caused by a cornea that is shaped more like a football than a basketball.

The Axis is a number anywhere between 0 and 180 degrees. It reveals the orientation of the astigmatism. It is not enough to specify how much astigmatism there is; you have to know where the difference in curvature is taking place.

Here are two examples of what prescriptions for eyes with astigmatism could look like:

-2.00 +1.50 x 180

+3.50 +3.00 x 45

The first prescription means that the person has 2 diopters of nearsightedness with 1.5 diopters of astigmatism and an axis of 180 degrees.

The second prescription means that the person has 3.5 diopters of farsightedness, 3 diopters of astigmatism and an axis of 45 degrees.
answered Feb 12, 2017 by layla

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