How to Read an Eyeglasses Prescription

It’s essential to understand how to read an eyeglasses prescription. This guide will help you better understand your prescription so you can order your new glasses more easily and accurately.

How to Read an Eyeglasses Prescription

Although there may be slight variations between different prescriptions (paper or digital), most eyeglass prescriptions are presented in a simple grid or table format with rows, columns, and labeled fields.

These prescriptions typically include a mix of standard abbreviations.

A key part of understanding your prescription is knowing what OD and OS mean. These terms are often written as O.D. and O.S. (from the Latin oculus dexter and oculus sinister), which refer to:

  • OD: Right eye
  • OS: Left eye

Some doctors may also use:

  • OU: Both eyes
  • RE / LE: Right eye / Left eye

Below are the most common abbreviations you may find in your prescription:

SPH (Sphere / Spherical Power)

SPH indicates the lens power needed to correct nearsightedness or farsightedness.

  • A minus sign (–) indicates nearsightedness
  • A plus sign (+), or no sign, usually indicates farsightedness
  • The higher the number (positive or negative), the stronger the prescription

CYL (Cylinder / Astigmatism Correction)

CYL represents the amount of lens power needed to correct astigmatism.

  • This value may also include a plus (+) or minus (–) sign
  • If you see “DS,” “SPH,” “spherical,” or “PL” in this field, it means there is no astigmatism correction needed

AXIS

AXIS describes the orientation of astigmatism correction and is measured in degrees from 1 to 180.
If a prescription includes a CYL value, it must also include an AXIS value.

ADD (Near Addition)

ADD refers to the additional magnifying power used for near vision.
It is commonly used for:

  • Bifocal lenses
  • Progressive lenses
  • Reading or computer (intermediate) glasses

PRISM

Prism correction is used to help align the eyes by bending light in a specific direction.
It is measured in prism diopters and usually written in 0.25 increments (e.g., 0.25, 0.50, 0.75, 1.00).
Unlike SPH and CYL, prism values do not include plus or minus signs.
When prism correction is included, the direction of the prism base must also be specified:

  • BU = Base Up
  • BD = Base Down
  • BI = Base In (toward the nose)
  • BO = Base Out (toward the ear)

Some prescriptions may include both horizontal and vertical prism corrections, and values may differ between the two eyes.

PD (Pupillary Distance)

PD is the distance between the centers of your pupils, measured in millimeters.
A dual PD may be provided in the format:

  • 31.5 / 31.5

This represents the distance from each pupil to the center of the nose bridge.
PD is very important for ensuring your lenses are properly centered, which helps provide clear and comfortable vision.
If your eye doctor does not include PD on your prescription, you can measure it yourself or request it from your optometrist.

2. Eyeglasses Prescription Examples

Below are common types of prescriptions:

  • Prescription for nearsightedness
  • Prescription for farsightedness with astigmatism
  • Progressive (multifocal) prescription
  • Prescription with prism correction

(Illustration examples may be shown here)

3. Important Notes

  • Eyeglass prescriptions can also be used to make sunglasses, but they cannot be used for contact lenses.
  • Prescription validity:
    Eye prescriptions are not permanent. Regular eye exams are recommended to ensure your vision remains accurate and healthy. In most cases, prescriptions are valid for 1–2 years, depending on local regulations. After expiration, a new eye exam is required.
  • If you have any difficulty understanding your prescription, please contact our customer support team. We are happy to help you choose and order your new glasses.