What does OD and OS mean on an eyeglass prescription?

OD (Oculus Dexter) means your right eye. OS (Oculus Sinister) means your left eye.

What does SPH mean on a prescription?

SPH (Sphere) is the main lens power. A minus (-) means nearsighted; a plus (+) means farsighted.

What is PD on an eyeglass prescription?

PD (Pupillary Distance) is the distance in millimeters between the center of your pupils. It is critical for centering lenses correctly and may be one number (e.g., 63) or two (e.g., 32/31).

How do I measure my PD at home?

Stand about 8 inches from a mirror. Hold a millimeter ruler flat against your brow. Close your right eye and align zero with the center of your left pupil. Open your right eye, close your left, and read the measurement at the center of your right pupil. Most adults are between 54mm–74mm.

Is my glasses prescription the same as my contact lens prescription?

No. Contact lens prescriptions include additional measurements (Base Curve and Diameter) and require a separate fitting with your eye doctor.

How long is an eyeglass prescription valid?

Most prescriptions are valid for 1–2 years. Check the date on yours before ordering online.

How to Read Your Eyeglass Prescription

Q: What does CYL mean on a prescription?

CYL (Cylinder) corrects astigmatism. If blank or 'DS', you don't have astigmatism.

Got a prescription from your eye doctor but not sure what all those numbers mean? You're not alone! Here's a simple breakdown so you can shop for frames with total confidence.

A Sample Prescription

	SPH	CYL	AXIS	ADD	PD
OD (Right Eye)	-2.50	-0.75	180	+2.00	32
OS (Left Eye)	-1.75	-0.50	175	+2.00	31

What Each Term Means

OD & OS

OD (Oculus Dexter) = your right eye. OS (Oculus Sinister) = your left eye.

SPH (Sphere)

The main lens power. Minus (-) = nearsighted. Plus (+) = farsighted.

CYL (Cylinder)

Corrects astigmatism. If blank or "DS" you don't have astigmatism.

AXIS

The orientation of your astigmatism correction. A number between 1-180.

ADD (Addition)

Extra magnification for bifocal or progressive lenses. Always a plus (+) number.

PD (Pupillary Distance)

The distance in millimeters between the center of your pupils. Critical for centering lenses correctly. May be one number (e.g., 63) or two (e.g., 32/31).

📏 How to Measure Your PD at Home

Your PD isn't always on your prescription — but you need it to order lenses online. Here's how to measure it in under 2 minutes:

What you'll need: A millimeter ruler and a mirror.

Stand about 8 inches from a mirror in good lighting.
Hold the ruler flat against your brow, just above your eyes.
Close your right eye. Align the zero mark with the center of your left pupil.
Open your right eye and close your left — without moving the ruler.
Read the measurement at the center of your right pupil. That's your PD!

Tips: Have a friend help for accuracy. Measure 2-3 times and average. Most adults are between 54mm–74mm.

💡 Still unsure? Send us your prescription and we'll help. For simple prescriptions, our in-house lab can often have your lenses ready within an hour when you call ahead!

📞 Call ahead & book your visit | 📧 Email us your prescription

Tips for Shopping Online

Have your prescription ready when you browse.
PD not on your prescription? Measure it at home using the guide above.
Prescriptions are typically valid for 1–2 years.
Not sure if your prescription works with a frame? Visit us or reach out — we're happy to help.

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