If you need eyeglasses, you might be confused by the numbers, terms, and symbols on your prescription. However, there are important reasons why it’s written the way it is. Eyeglasses prescriptions are written in a standardized format that is used all over the world. This makes it easy for eye care professionals to understand your prescription, no matter where you go.
Latin Abbreviations in Eyeglass Prescriptions
Eyeglass prescriptions often use Latin abbreviations. While these abbreviations have been used for centuries, they are becoming less common. In recent years, many eye care providers have switched to using abbreviations that are more specific and easier to understand.
For example, the word “power” is sometimes written as “PWR” on a prescription. Another common term is “sphere” which is sometimes abbreviated as “SPH.” These abbreviations are more specific than the Latin abbreviations, and they are easier for patients to understand.
If you are not sure what the abbreviations on your eyeglass prescription mean, you can always ask your eye care provider for clarification. They will be able to explain the abbreviations and help you to understand your prescription.
What Do the Numbers Mean in Eyeglass Prescriptions?
In addition to terms and abbreviations, eyeglass prescriptions also include a numerical value that indicates the strength of the lenses needed to correct your vision. The numbers are typically followed by a plus sign (+) or minus sign (-), which indicates whether you are nearsighted or farsighted.
Nearsightedness is when you can see objects close up clearly, but objects farther away are blurry. The plus sign (+) in a prescription indicates nearsightedness, and the higher the number, the stronger the lenses needed to correct your vision.
Farsightedness is when you can see objects far away clearly, but objects close up are blurry. The minus sign (-) in a prescription indicates farsightedness, and the higher the number, the stronger the lenses needed to correct your vision.
The sphere part of your eyeglass prescription, also known as SPH, indicates whether you have nearsightedness or farsightedness. Nearsighted people have trouble seeing things that are far away, while farsighted people have trouble seeing things that are up close. The sphere number is a measurement of how strong your prescription is, and it is represented by a plus (+) or minus (-) sign before the number.
The cylinder measurement in a prescription indicates the degree of astigmatism in your eye. Astigmatism is a condition in which the cornea (the clear front part of your eye) is not perfectly round. This can cause blurred vision, especially when you look at objects up close or in the distance.
The axis number on your eyeglass prescription indicates the direction of your astigmatism. Astigmatism is a common eye condition that causes blurry vision. The axis number is measured in degrees from 0 to 180, and it refers to the angle of the astigmatism in your cornea. The cornea is the clear covering of your eye that helps focus light.
The ADD number in a prescription indicates the amount of additional power needed to see clearly at close distances. This is especially important for people over the age of 40, as they typically develop near-focusing problems.
The ADD number is typically added to the distance prescription to create a bifocal or progressive lens. Bifocal lenses have two different prescriptions in one lens, one for distance and one for near. Progressive lenses have a gradual change in prescription from distance to near, so there is no visible line between the two.
ADD vs. Powers for Readers
Many people mistakenly believe that the ADD number is the power needed for over-the-counter reading glasses. However, this is not the case. The ADD number is the additional power needed for near vision, and it must be added to the sphere number to get the correct power for reading glasses.
For example, if your prescription is -2.00 in the right eye and +1.75 ADD, the correct power for reading glasses would be -0.25. Similarly, if your prescription is +1.00 in the left eye and +1.75 ADD, the correct power for reading glasses would be +2.75.