Eyeglass Prescription
OD, OS, SPH, CYL, AXIS - your prescription can look like a foreign language. This guide explains every number and abbreviation so you can order glasses with total confidence.
Your eyeglass prescription is written by your optometrist or ophthalmologist after an eye exam. It contains specific measurements that tell lens makers exactly how to correct your vision. Understanding what each field means makes it easy to enter your prescription when ordering glasses online - and helps you catch any errors before they become a problem.
An eyeglass prescription is a written order from a licensed eye care professional that specifies the corrective lenses you need. It is the result of a refraction test during your eye exam, where your doctor determines the exact lens power needed to bring your vision to 20/20 (or as close as possible).
A prescription is not the same as a contact lens prescription - the two are not interchangeable. Always use your glasses prescription when ordering frames with lenses.
Most prescriptions expire after 1-2 years. Check the expiration date before ordering.
Prescriptions always list the right eye (OD) first, then the left eye (OS) below it.
Your glasses Rx and contact lens Rx are different. Only use your glasses prescription here.
Most eyeglass prescriptions follow a standard format with rows for each eye and columns for each measurement. Here is a typical example:
| Eye | SPH | CYL | AXIS | ADD |
|---|---|---|---|---|
| OD (Right) | -2.50 | -0.75 | 180 | +2.00 |
| OS (Left) | -3.00 | -1.00 | 170 | +2.00 |
A typical printed eyeglass prescription - yours may look slightly different depending on your eye doctor.
Every column on your prescription has a specific meaning. Here is what each one tells your lens maker:
OD (Oculus Dexter) = Right eye. OS (Oculus Sinister) = Left eye. Your prescription always lists OD first. Some forms use RE (right eye) and LE (left eye) instead.
The amount of lens power needed to correct your distance vision, measured in diopters (D).
Nearsighted (myopia) - you see close objects clearly but distant objects are blurry.
Farsighted (hyperopia) - you see distant objects more clearly but struggle up close.
The higher the number (ignoring the sign), the stronger the prescription. A -0.50 is very mild; a -6.00 is quite strong.
The lens power needed to correct astigmatism - an imperfection in the curvature of your eye. If this field is blank, zero, or shows DS/SPH, you do not have astigmatism and your lens is spherical. CYL can be written as a minus or plus number depending on how your doctor writes prescriptions.
A number between 1 and 180 that describes the angle (in degrees) of the astigmatism correction. It works together with CYL - if your CYL is blank, there is no AXIS. The AXIS tells the lab which direction to orient the cylinder in the lens.
OD, OS, SPH, CYL, and AXIS are the five core fields on every eyeglass prescription.
Not everyone has these on their prescription - but if you do, here is what they mean:
The extra magnifying power added to the bottom of bifocal or progressive lenses for reading. Always a positive number, typically between +0.75 and +3.00. Most common in people over 40 who are developing presbyopia (age-related difficulty reading up close). If you do not need bifocals or progressives, your prescription may not have an ADD value.
Prismatic correction helps align images for people whose eyes do not work together properly (a condition called strabismus or binocular vision disorder). Most people do not have prism on their prescription. It is measured in prism diopters and comes with a direction: BU (base up), BD (base down), BI (base in), or BO (base out).
The distance in millimeters between the centers of your pupils. Needed to position your prescription lenses correctly in the frame so your eyes look through the optical center. Your doctor may list it as one number (e.g. 64) for both eyes combined, or two separate numbers (e.g. 32/32) for right and left eye individually.
ADD, Prism, and PD are secondary fields - not everyone has all three on their prescription.
Most prescriptions expire in 1-2 years. An expired prescription cannot be used to order glasses. If yours has expired, visit your eye doctor for an updated exam.
Always include the plus or minus sign when entering SPH and CYL values. A -2.50 and +2.50 are completely different prescriptions. Missing a sign is the most common ordering mistake.
It is very common for your right and left eye prescriptions to be different. Enter each eye's values separately and double-check before placing your order.
If your CYL field says DS, SPH, or is blank, it means no astigmatism correction is needed. Leave the CYL and AXIS fields empty when ordering.
If SPH shows PL or Plano, it means 0.00 - no sphere correction needed in that eye. This is common in one eye when only the other eye needs vision correction.
When you order at Shade Gray, you can upload a photo of your prescription and our team will verify the details before processing your lenses.
