How to Read an Eyeglass Prescription: SPH, CYL, AXIS & ADD

A simple guide to understanding the numbers on your prescription before ordering glasses online.

Learn how to read your eyeglass prescription, including SPH, CYL, AXIS, ADD, PD and prism values, with clear examples before ordering glasses online.

On a typical eyeglass prescription, OD (Oculus Dexter) refers to the right eye and OS (Oculus Sinister) to the left eye. Common fields include SPH, CYL and AXIS; some prescriptions also include ADD, PD and Prism.

Prescription Example: Where to Find Each Value

Illustrative sample only. Your prescription values and format may look different.

What the Prescription Terms Mean

Term	What It Means	What to Look For
SPH Sphere	Main lens power	Minus (-) usually indicates nearsightedness; plus (+) usually indicates farsightedness or near-vision power.
CYL Cylinder	Amount of astigmatism correction	CYL may use a plus (+) or minus (-) sign.
AXIS Axis	Direction of astigmatism correction	Written as a whole number from 1 to 180 when CYL is present.
ADD Addition	Extra plus power for near vision	Commonly used for bifocal and progressive lenses.
PD Pupillary Distance	Distance between pupil centers	In millimeters; may be one total PD or two monocular PD values.
Prism Prism Correction	Optional eye-alignment correction	Shown with a prism value and base direction such as BU, BD, BI or BO.

For Distance Correction

Distance prescriptions normally include SPH for each eye. If astigmatism correction is needed, CYL and AXIS are also listed. D.V. may be used for distance vision.

For Reading-Only Correction

Reading prescriptions may list near-vision powers directly or use a distance prescription plus ADD. Enter the values exactly as written; do not estimate or convert them yourself.

For Astigmatism Correction

CYL and AXIS work together. If CYL is present, there should normally be a corresponding AXIS value.

Check the plus (+) or minus (-) sign carefully.
If there is no astigmatism correction, CYL/AXIS may be blank or marked SPH/DS.
AXIS is a whole number from 1 to 180; 5, 005 and 5° mean the same axis.

For Bifocals and Progressive Lenses (ADD)

ADD is extra plus power for near vision. If one ADD value is shown, it commonly applies to both eyes unless noted otherwise. “PAL” may indicate progressive addition lenses. Viewner processes ADD powers from +1.00 to +3.50.

How to Read PD (Pupillary Distance)

PD centers the lenses in front of your eyes. It may be shown as one total PD (for example, 63 mm) or two separate monocular PD values.

If PD is not listed, use an accurate PD measurement before ordering.

How to Read Prism

Prism is not included on every prescription. When prescribed, it may be written in prism diopters (Δ) with a base direction: BU, BD, BI or BO.

Enter prism exactly as written. If it is unclear, confirm it before placing the order.

Important Notes Before Entering Your Prescription

Check every plus (+) and minus (-) sign carefully.
Do not guess if a decimal point, handwritten number or abbreviation is unclear.
Make sure OD values are entered for the right eye and OS values for the left eye.
If you are unsure about SPH, CYL, AXIS, ADD, PD or Prism, send a clear photo of the prescription to Customer Service.

Need Help Reading Your Prescription?

If anything on your prescription is unfamiliar, please contact the Viewner Customer Service team. We can help you identify the fields before you enter the prescription online.