Eyeglass prescriptions list SPH, CYL, AXIS, ADD, PRISM, and PD; match each label to its meaning to order lenses with confidence.
That line of abbreviations on your slip isn’t random. It’s a precise map for lens power, orientation, and fit. Learn what each label means, then follow the steps to decode your numbers and pick frames or lenses with fewer surprises.
Reading An Eyeglass Prescription: Step-By-Step
Pull out the page or PDF. You’ll see rows for each eye and columns labeled with short tags. Start with the right eye, then the left. Move across each column, matching the tag to the plain-English meaning below.
Quick Reference: Common Tags And What They Mean
| Tag | Meaning | What You Do With It |
|---|---|---|
| OD / OS / OU | Right eye / left eye / both eyes | Read each row for the correct eye |
| SPH | Main lens power in diopters; “−” for nearsight, “+” for farsight | Sets overall focusing power |
| CYL | Astigmatism strength | Paired with AXIS to shape the lens |
| AXIS | Astigmatism angle from 1–180 | Aligns the cylinder in the lens |
| ADD | Extra plus power for near work | Used for bifocal or progressive zones |
| PRISM / BASE | Prism strength and direction | Aligns images for double vision |
| PD | Pupillary distance in millimeters | Centers lenses to your eyes |
| Seg Height | Vertical placement for the near zone | Used for multifocals |
| VA | Visual acuity with the Rx | Shows expected clarity with glasses |
Why Plus And Minus Matter
A minus sign on SPH means you see better far away with help, so lenses reduce power to shift focus forward. A plus sign does the opposite and brings near objects into focus. The higher the number, the stronger the lens.
Astigmatism: CYL And AXIS As A Pair
Astigmatism isn’t a disease; it’s a shape issue. The surface curves more in one meridian than another, so light spreads. CYL gives the strength needed to fix that spread. AXIS tells the lab where to place that correction on the lens. AXIS runs 1–180 and pairs with CYL only; no CYL means no AXIS.
ADD Power For Reading And Screens
ADD is extra plus power layered on top of the distance numbers. It helps with small text and near tasks. You’ll see it in bifocals and progressives. Typical ADD values for adults land between +0.75 and +3.00, moving upward with age and near-focus strain.
Prism And Base Direction
Prism shifts images to help the eyes work together. Strength is in prism diopters, and direction is tagged as Base In (BI), Base Out (BO), Base Up (BU), or Base Down (BD). Many prescriptions won’t include prism; if yours does, make sure frames are adjusted well, since small tilts can change how prism feels.
Decode Your Lines Like A Pro
Use this simple flow when you read your sheet. Keep a pencil handy and mark each piece as you go.
1) Confirm The Eye Rows
OD is the right eye. OS is the left. OU stands for both eyes together. If your sheet has only one eye filled, that’s normal for post-surgery checks or single-vision cases.
2) Read SPH First
Check the sign and number. A −2.00 means moderate nearsight. A +1.50 means mild farsight. If SPH shows “plano” or “DS,” that eye has no distance power and may only show astigmatism or prism lines.
3) Look For CYL And AXIS
If CYL is blank, there’s no astigmatism correction. If it’s present, move straight to AXIS on the same row. Numbers near 180 or near 90 are common, but any value from 1–180 is valid when paired with CYL.
4) Find ADD If You Use Multifocals
ADD sits in its own column or under a near section. Both eyes often share the same ADD, though not always. Higher ADD means stronger help at near distance.
5) Check For PRISM
Look for a prism value and a base direction (BI, BO, BU, BD). If present, be sure the lab and fitter follow it closely. Small placement errors can feel uncomfortable.
6) Record PD And Any Seg Height
PD may be written as a single number (total) or split (right/left). Seg height appears for bifocals or progressives and depends on the frame you pick and how it sits.
Trusted Rules And Definitions
You’re allowed a copy of your lens specs after your exam under the federal Eyeglass Rule. Some states require that the pupillary distance be included to help with online orders. See the FTC Eyeglass Rule for wording and timing. For clear wording on SPH, CYL, AXIS, and ADD, review this plain guide from the American Academy of Ophthalmology.
Make Sense Of Formatting
Layout varies by clinic or retailer, but the core tags stay the same. Signs, decimals, and blanks carry meaning. Use the notes below when a sheet looks unfamiliar.
Where The Numbers Sit On Typical Forms
Distance power columns sit left, often next to OD and OS. Astigmatism fields sit in the middle, with CYL beside AXIS. Near power sits under ADD, placed near the right side or under a “near” header. PD can appear at the bottom or in a fitting section. If your sheet lists dual PD, it may show “R” and “L” values beside the total. This layout pattern helps you scan fast, even when the fonts or grid lines change from one printout to another.
Pluses, Minuses, And Zeros
A number without a sign is assumed positive. “+0.00,” “0.00,” and “plano” all point to no distance power. If CYL is written as “DS” (diopters sphere) in the CYL box, there’s no cylinder; the box holds the placeholder only.
Single PD Vs. Dual PD
A single value like 63 mm means the total both-eye distance in millimeters. Dual values split the total, such as 31.5 / 31.5, or 32 / 31. Dual PD helps center each lens more precisely in the frame.
Axis Ranges And Rounding
AXIS uses whole numbers from 1–180. Labs can round to the nearest whole degree. Tiny changes in AXIS can shift clarity for strong CYL powers, so check the fit if things feel off.
Lens Buying Steps With Real Numbers
Here’s a simple path from paper to frames. Follow this order; it reduces remakes and returns.
Pick A Frame That Fits
Choose a bridge that sits level and pads that don’t pinch. Strong nearsight or strong astigmatism pairs better with modest eye sizes to keep lenses thinner.
Match Lens Type To Your Day
Single-vision handles one distance. Readers add near power only. Bifocals give two zones with a line. Progressives blend distance to near without a line. If your sheet lists prism, confirm that your lens choice supports it.
Choose Materials And Coatings
Standard plastic is fine for mild powers. High-index thins strong powers. Polycarbonate and Trivex add impact resistance and lighter weight. Add anti-reflective for screen glare and night driving; add scratch-resist for durability.
Give The Lab Clean Inputs
Provide SPH, CYL, AXIS, and ADD for each eye. Provide PD and, for multifocals, the seg height based on your chosen frame. Share any prism with base directions. Ask for lens centration matching the PD to avoid off-center optics.
Common Prescription Lines, Decoded
Use this chart to translate frequent tags and decide your next action.
| What You See | Plain Meaning | Next Step |
|---|---|---|
| OD: −2.00 / OS: −1.75 | Nearsight both eyes | Single-vision distance lenses |
| CYL: −1.50 AXIS: 180 | Astigmatism corrected at 180° | Check AXIS stays at 180° in the order |
| SPH: +2.00 ADD: +2.00 | Farsight with near boost | Ask for bifocals or progressives |
| PRISM: 1.0 BI | Base In prism for eye teaming | Confirm frame alignment after dispense |
| PD: 31 / 31 | Dual PD for precise centration | Provide both numbers to the lab |
Quick Clarifications Buyers Ask
Does The Sheet Include Expiration?
Many regions set a time limit. If the page shows a date, use it. If not, call the clinic. Retailers follow local rules for validity.
Why Doesn’t My Page List PD?
Some clinics record PD in fitting software instead of the printed page. If you plan to buy online, ask the office for the number. The FTC encourages releasing PD on request to help with orders under the same rule mentioned above.
Is A Contact Lens Page The Same?
No. Contact lens pages include base curve, diameter, brand, and other fit data. Don’t use a contact page to buy eyeglass lenses.
Real-World Tips For Fewer Remakes
Keep A Photo Of Your Page
Snap a clear photo right after your visit. This saves back-and-forth later.
Stick With One Measurement Set Per Order
Don’t mix PD or seg height values from different sources in one order. Use one complete set so centering stays consistent.
Check Fit Before You Leave
When you pick up your glasses, ask for minor adjustments. Small tweaks at the nose pads or temples can clear up blur, especially with astigmatism or prism.
Know When To Call
If straight lines bend or if letters swim, call the clinic. A small AXIS adjustment or a different frame tilt can solve it.
Field Glossary For Fast Lookups
Keep this short list handy while you order.
SPH
Overall lens power in diopters; minus for nearsight, plus for farsight.
CYL
Astigmatism strength in diopters; pairs with AXIS only.
AXIS
Angle from 1–180 degrees showing where the cylinder sits.
ADD
Extra plus power for near tasks in bifocal or progressive designs.
PRISM / BASE
Strength and direction used to align images (BI, BO, BU, BD).
PD
Center-to-center eye distance in millimeters; may be total or split.
Final Check Before You Order
Confirm eye labels. Copy SPH, CYL, AXIS, and any ADD exactly. Include prism and base if shown. Provide PD and seg height tied to your chosen frame. Save a copy of everything you send. With the tags above, you can read your page line by line and order lenses with far fewer hiccups.