How strong is my eye prescription?

Deciphering your eye prescription should be less about how “bad” it is, and more about how vision correction can improve your eyesight. The goal of glasses and contacts is always 20/20 vision, no matter what your prescription reads.

The numbers, decimals, pluses and minuses may seem like a language spoken only by eye doctors, but their meanings are more straightforward than you might think: They all relate to common eye conditions in some way.

The column labeled “Sphere” is especially useful, since a value closer to zero represents a more mild condition. But there’s more the numbers in your prescription can tell you about nearsightedness, farsightedness (including presbyopia) and astigmatism.

Sphere (or SPH)

This stands for “spherical error”; it represents how nearsighted or farsighted you are.

In the sphere column, do you see a minus sign followed by numbers in each row? That means you’re nearsighted, and closer objects may appear more clearly.

If you see plus signs followed by numbers, you’re farsighted, meaning you can see objects better when they’re farther away.

To find out how extensive your nearsightedness or farsightedness is, move to the numbers next to the plus or minus signs.

For the nearsighted, levels of severity fall into the following categories:

• If your number is between -0.25 and -2.00, you have mild nearsightedness
• If your number is between -2.25 and -5.00, you have moderate nearsightedness
• If your number is lower than -5.00, you have high nearsightedness

For the farsighted, severity is classified this way:

• If your number is between +0.25 and +2.00, you have mild farsightedness
• If your number is between +2.25 and +5.00, you have moderate farsightedness
• If your number is greater than +5.00, you have high farsightedness

For both types, the closer you are to zero, the better your vision is.

For example, even though measurements of -0.75 and -1.25 both qualify as mild nearsightedness, the person with a spherical error of -0.75 is technically closer to 20/20 vision without their glasses on.

READ MORE: What is a diopter?

Cylinder (or CYL)

This value only applies to people who have astigmatism, a common problem with the curvature of the cornea in front of the pupil.

The larger this number is, the more significant the level of astigmatism is. More significant astigmatism can mean a greater effect on your unassisted vision quality.

Axis

If you have a cylinder number listed, you’ll also have an axis number. This is only an angular measurement of astigmatism.

Add

This specifically relates to presbyopia, the loss of your ability to focus on near objects as you age. Presbyopia is a normal part of the aging process, and it usually kicks in sometime after age 40.

The add value — short for added magnifying power —  relates to the bottom part of the lens in multifocal or bifocal glasses. Unlike sphere and cylinder, this is always a positive number (even if it isn’t always preceded by a plus sign). The higher the add number, the more powerful the lens is.

PD

PD stands for pupillary distance, the space between your eyes’ pupils in millimeters.

It’s common for two different PD measurements to be present. This means one pupil is a little further from your nose than the other one. This can be as little as one millimeter and has no effect on vision power.

Prism 

While the prism field is less common than the ones listed above, it’s important for those who need it, as it’s used to address eye alignment issues. For more information on what this means, along with additional insight, check out our full guide on  how to read your glasses prescription. 

Working together 

Everyone’s eyes are different, and these measurements all come together to make sure you’re seeing as close to 20/20 as possible. 

Your vision will almost always be slightly better or worse than the next person’s. But modern exam technology, high-quality lens manufacturing and qualified eye care professionals work hand in hand to make clear vision a possibility for everyone.