You've just received your eye prescription, looked at the numbers, and thought: what does all of this actually mean? Terms like OD, OS, SPH, CYL, AXIS, ADD, and PD can make an eyeglass prescription look complicated. But once you understand what each abbreviation means, reading your prescription becomes surprisingly simple.

Your prescription is essentially a set of precise measurements that tells an optical professional how your lenses should be made to correct your vision. By the end of this guide, you'll be able to look at your prescription and understand exactly what every number means.

The Quick Answer: What a Prescription Looks Like

A typical eyeglass prescription may look something like this:

Eye	SPH	CYL	Axis	ADD
OD	-2.00	-0.75	180	+1.50
OS	-1.50	-0.50	170	+1.50

At first glance, this may look confusing. But each part has a specific meaning:

• OD = Right eye
• OS = Left eye
• SPH = Main lens power
• CYL = Astigmatism correction
• AXIS = Direction of astigmatism correction
• ADD = Extra power for reading
• PD = Pupillary distance

The key to understanding an eye prescription is to read each column one at a time.

Step 1: What Do OD and OS Mean?

Some prescriptions use simpler abbreviations instead: RE / R/E for right eye, LE / L/E for left eye. You may also occasionally see OU, meaning both eyes.

Step 2: What Is SPH in an Eye Prescription?

SPH, or Sphere, is the main lens power in your prescription — it tells you the basic amount of vision correction your lens needs, measured in diopters (D). The number may have either a minus sign (–) or a plus sign (+).

What Does Plano or PL Mean?

Sometimes instead of a regular SPH number, you'll see PL, Plano, or 0.00. This generally means no spherical correction is required — but a person can still have other prescription values, such as CYL and AXIS, even with a Plano SPH.

Step 3: What Is CYL in an Eye Prescription?

CYL stands for Cylinder and represents the amount of correction needed for astigmatism — a refractive error related to the way light focuses in the eye. A CYL value may look like -0.50, -0.75, -1.25, or +1.00. Not everyone has a CYL value; if the box is blank, zero, or marked differently, it may indicate no significant cylindrical correction has been prescribed.

Think of CYL as an additional correction that works alongside the main SPH power. Your prescription may include SPH only, SPH + CYL + AXIS, or Plano + CYL + AXIS. If CYL appears, you'll usually also see an AXIS value, since the two work together.

Step 4: What Is AXIS in an Eye Prescription?

AXIS tells the optical lab the direction in which the CYL correction should be positioned. It's written as a number between 1 and 180 degrees — for example, 10, 45, 90, 135, or 180.

Step 5: What Is ADD Power in an Eye Prescription?

ADD, sometimes called Addition, is extra plus power used for near vision — commonly relating to reading and close-up tasks. ADD values may look like +1.00, +1.50, +2.00, or +2.50, and are commonly used in progressive lenses, bifocal lenses, and other multifocal designs.

As people get older, many experience presbyopia, an age-related change that makes focusing on close objects more difficult. The ADD value provides the additional power needed for near vision.

Reading a Progressive Prescription

Eye	SPH	CYL	Axis	ADD
OD	-2.00	-0.50	180	+2.00
OS	-1.75	-0.75	170	+2.00

The SPH, CYL, and AXIS values describe the distance prescription and astigmatism correction. The ADD +2.00 provides the additional power for near vision within a multifocal lens design. If your prescription includes ADD, make sure the lens type you select is appropriate for it.

Step 6: What Is PD in Glasses?

PD stands for Pupillary Distance — the distance between the centers of your pupils, generally measured in millimeters (e.g., 60mm, 62mm, 63mm, 64mm). PD matters because the optical center of your lenses needs to be positioned correctly in front of your eyes, which becomes especially important when ordering glasses online and for certain multifocal lenses.

Your PD may be written as a single number (63mm) or as two separate monocular measurements (31.5 / 31.5) representing each eye individually. Never guess your PD when precise measurements are required.

Step 7: What Is Prism in an Eye Prescription?

Some prescriptions include Prism correction, which is less common than SPH, CYL, and AXIS. If Prism appears, it's usually accompanied by a Base direction, such as Base In, Base Out, Base Up, or Base Down. Prism is used for specific visual and eye-alignment requirements — if your prescription includes it, make sure your glasses are made exactly according to the prescription and measurements your eye-care professional provided.

A Complete Worked Example

Eye	SPH	CYL	Axis	ADD
OD	-2.50	-0.75	180	+1.50
OS	-1.75	-0.50	170	+1.50

Eyeglass Prescription Chart: Quick Reference

Term	Meaning
OD	Right Eye
OS	Left Eye
OU	Both Eyes
SPH	Main spherical lens power
CYL	Astigmatism correction
AXIS	Direction of cylinder correction
ADD	Additional power for near vision
PD	Pupillary distance
Prism	Special correction for certain eye-alignment needs
PL / Plano	No spherical correction

A Few Common Questions About Reading Your Prescription

How Do You Know If Your Prescription Is Strong?

In general, the number farther from zero represents a stronger amount of correction — -1.00 is less powerful than -5.00, and +1.00 is less powerful than +4.00. But there's more to a prescription than just the SPH number: CYL, AXIS, ADD, and Prism all factor in too. A higher number doesn't automatically mean something is wrong with your eyes — it simply indicates the amount and type of optical correction prescribed.

Can Your Right and Left Eye Have Different Prescriptions?

Yes — very commonly. For example, OD might be -3.00 while OS is -1.50. This means the two eyes require different amounts of correction. Always enter the OD and OS values exactly as they appear, and never switch them.

Can You Have CYL Without SPH?

Yes. A person may have little or no spherical correction (Plano) but still require astigmatism correction, such as Plano SPH with CYL -1.00 at AXIS 180.

Can You Have CYL Without AXIS?

Generally, no — CYL correction needs an AXIS value to specify its orientation. CYL tells the amount of astigmatism correction; AXIS tells the direction. Both values matter when reading and entering a prescription.

Common Mistakes People Make When Reading a Prescription

How to Check Your Prescription Before Ordering Online

Eyeglass Prescription vs Contact Lens Prescription

Not always the same. An eyeglass prescription and a contact lens prescription aren't automatically interchangeable — contact lenses sit directly on the eye, while eyeglass lenses sit at a distance in front of the eyes. Contact lens prescriptions may also include additional measurements and specifications. Always use the appropriate prescription for the type of vision correction you're ordering.

Frequently Asked Questions

Your eye prescription may look like a complicated combination of numbers and abbreviations, but every value has a specific purpose. The most important terms to remember are OD (right eye), OS (left eye), SPH (main lens power), CYL (astigmatism correction), AXIS (direction of that correction), ADD (extra near-vision power), and PD (pupillary distance).

Your prescription is not just a collection of random numbers — it's a precise map designed to help your lenses provide the clearest, most comfortable vision possible.