When you look at your prescription for eyeglasses, you will see numbers listed under the headings of OS (Latin abbreviation for oculus sinister; means your left eye) and OD (Latin abbreviation for oculus dextrus; means your right eye). Perfect eyesight would mean your eyes would score a zero. The further away from zero the number on your prescription, the worse your eyesight and the stronger prescription you need. A “plus” (+) sign in front of the number means you are farsighted, and a “minus” (-) sign means you are nearsighted. In some rare cases, your prescription may also include a column labeled “OU”, which means both eyes.
For example, if your prescription says -0.75, you have a fairly low amount of nearsightedness. If you are -5.25, that means you have higher amount of nearsightedness, and would requires stronger (thicker) lenses. Similarly the opposite, if you had a +1.25 would be a small amount of farsightedness and +4.75 would be more. All of our glasses come with a thin 1.59 index polycarbonate lens, which would be a significant upgrade at a substantial cost on other websites.
For people who have astigmatism, there will be three numbers in your prescription. You will see "Sphere", "Cylinder" and "Axis"
The "Sphere" number on a prescription, is the degree of nearsightedness or farsightedness.
The "Cylinder" or your astigmatism level, and can be either negative or a positive number. It measures the degree of astigmatism that you have. The bigger this number, the more astigmatism you have.
The "Axis" is a number anywhere between 0 and 180 degrees. It reveals the position of the astigmatism. It is not enough to specify how much astigmatism there is; you have to know where the difference to what degree the curve of it is.
Prism - Some people may need to add a prism value. A prism number indicates the amount of prismatic power, needed to compensate for any alignment problems in your eyes. People with a prism tend to see things double or very blurry. In this case adding prism to your lens would alleviate this problem.
Base - This column indicates the direction of a prism by showing the relative position of its thickest edge. If the base is directed upwards (Vertical Prism), the column will read "base up". If the base is directed down, it will read "base down". If the base is directed toward the wearer's nose (Horizontal Prism), the column will read “base in". If the base points away from the wearer's nose and toward the ear, the column will read "base out".
NV ADD - Is the number associated with either of these terms indicates the additive power needed to correct your immediate near vision if your prescription is for distance correction. This number is typically added if you need a multifocal prescription for both near and far.
PD also known as Pupillary Distance - Is needed for all prescriptions. This number indicates the distance from the center of one pupil to the center of the other, and is an important number to customize your lens. In some cases you may have a Dual PD. This would give a different measurement for each eye as opposed to one measurement for both.