An eyeglass prescription lists SPH, CYL, AXIS, ADD, PRISM, and PD; SPH sets lens power, CYL/AXIS fix astigmatism, and ADD boosts near vision.
Cracking a glasses Rx gets easy once you know what each line means and how the signs work. This guide walks you through every part of a spectacle prescription, the order to read it, and the quick checks that keep mistakes out of your cart at the optical shop.
Start With OD, OS, And OU Labels
You’ll see three common tags at the left edge of the Rx grid:
- OD = right eye (from the Latin oculus dexter)
- OS = left eye (from oculus sinister)
- OU = both eyes (shared value)
Some printouts swap in “Right” and “Left.” The rest of the line belongs to that eye only unless the form shows a shared figure under OU.
Field-By-Field Meanings (Broad Reference)
This compact table decodes the labels you’ll see on most printouts. Keep it open while you read the rest of the guide.
| Field | What It Controls | How It’s Written |
|---|---|---|
| SPH (Sphere) | Overall lens power for near- or far-sightedness | Diopters with a + or − sign; “PL” or “Plano” = zero |
| CYL (Cylinder) | Amount of astigmatism correction | Diopters, often negative; can be blank if none |
| AXIS | Orientation of astigmatism correction | 1–180 degrees; appears only when CYL is present |
| ADD | Extra power for near segments/progressives | Usually +0.75 to +3.50 D; same in both eyes often |
| PRISM / BASE | Alignment aid for double vision or eye teaming | Prism diopters with base direction (BU, BD, BI, BO) |
| PD (Pupillary Distance) | Centers lenses to your pupils | Millimeters; one number (binocular) or two (mono) |
| VA / NV / DV | Vision acuity or distance vs. near tags | Chart lines (like 20/20) or labels near entries |
| Lens / Seg Ht / Notes | Material, segment height for multifocals, remarks | Free text from the prescriber or the lab form |
Reading The Signs: Plus, Minus, And Plano
Sphere sets the base power. A minus sign means the lens corrects near-sighted blur. A plus sign means the lens corrects far-sighted blur. If the line shows “PL” or “Plano,” that eye needs no base power for distance.
Cylinder adds targeted power for astigmatism. If CYL is blank, there’s no astigmatism correction. If CYL has a number, it must be paired with an Axis between 1 and 180 degrees that tells the lab where to orient that correction on the lens.
ADD is the boost for close work in progressives, bifocals, and readers. It stacks on top of the distance SPH in the lower viewing area of the lens.
How To Read Your Eyeglasses Rx Step-By-Step
Use this order and you won’t miss anything:
- Confirm the eye line. Make sure you’re on OD or OS as you scan across.
- Note SPH with its sign. Bigger numbers mean stronger lenses.
- Check for CYL. If present, write down CYL and its AXIS together as a pair.
- Look for ADD if you wear progressives, bifocals, or task readers.
- Scan for PRISM entries and their base directions (BU/BD/BI/BO).
- Record PD. If two numbers appear (e.g., 31 / 32), that’s monocular PDs.
- Read any notes. You might see material suggestions, tint, or segment height.
Common Abbreviations And What They Mean In Practice
Here are the usual short forms you’ll bump into while ordering or checking a lab ticket.
- DV / NV: distance vision vs. near vision tags
- PL / Plano: zero power
- BAL: balance lens to match thickness when one eye has much more power
- VA: measured acuity on the chart, often added after dispensing
- BASE: prism base direction (BU up, BD down, BI toward nose, BO toward ear)
What The Numbers Feel Like Day To Day
Small SPH values (like −0.50) sharpen street signs and screens but won’t feel heavy. Midrange values (around −2.00 to −4.00 or +2.00) are everyday wear. Larger powers change lens thickness and weight; that’s where material choice and frame fit matter more.
With CYL, a low figure (−0.50) trims a mild smear or ghosting. A higher figure with a precise Axis will make edges snap into place in a certain orientation, which is why the axis must be exact.
ADD values under +1.25 suit early near-strain. Higher ADDs push more close-up clarity but shrink the in-focus window, so frame fit and segment height need care.
PD: The Small Number That Prevents Big Headaches
Pupillary distance (PD) tells the lab where to center the optical sweet spot of each lens. Adult PD often lands near the low-60s in millimeters, but it can sit well outside that range. A single figure is binocular PD. Two numbers split left and right for monocular PD.
If you want to see a clear, medical explanation of this measurement and when precision matters, check this pupillary distance guide from a major hospital system. It also flags why self-measuring can miss the mark for progressives and constant wear.
When ADD, Prism, And Segment Height Appear
ADD shows up on multifocal jobs. If you only need distance or only near, you may not see it. Prism appears when eye teaming needs help; the base direction tells the lab where the thicker edge points. Segment height sets where the near field starts in bifocals or where the progressive corridor sits inside the frame.
Close Variation: Reading A Glasses Prescription With Confidence
This section expands on the tricky bits people get wrong when they try to enter numbers online or compare printouts across clinics.
Axis Must Travel With Cylinder
No CYL, no Axis. If a sheet shows an axis but CYL is blank, that’s a formatting quirk; labs only cut an axis when CYL has power. Axis is a compass bearing on the lens surface, not a sign of severity.
Plus Vs. Minus Cylinder Formats
Some doctors write CYL in plus format, others in minus. Both describe the same optics. Labs can transpose one format into the other without changing how you see. If you’re re-ordering, stick with one format to reduce entry slips.
ADD Is Always Positive
ADD numbers are written as positive values. They stack onto the distance SPH in the lower zone of the lens. That’s why progressives list both SPH and ADD for each eye.
Prism Needs A Direction
A prism figure by itself isn’t complete. The base direction (BU, BD, BI, BO) is part of the order. BI points toward your nose; BO points toward your ear; BU points up; BD points down.
Sample Prescriptions Decoded
Use these patterns to sanity-check your own sheet before you buy.
| Sample Entry | What It Means | Notes |
|---|---|---|
| OD: −2.00 / −0.75 × 170 | Right eye is near-sighted with mild astigmatism at axis 170 | Distance-only unless ADD is listed |
| OS: +1.25 / PL | Left eye is far-sighted; no astigmatism | “PL” means zero CYL; axis is absent by design |
| ADD: +2.00 (OU) | Near boost for both eyes | Used in progressives or bifocals |
| Prism: 1.0 BO (OD) | One prism diopter base-out in right lens | Helps alignment; must include base |
| PD: 31 / 32 | Monocular PDs: 31 mm right, 32 mm left | Enter as two numbers when a site asks |
Putting The Numbers To Work When You Order
Match Frame Size To Your PD
A frame that’s too wide can push lenses off-center. That can add eye strain even with a perfect Rx. If a tool asks for PD, use the exact figure from your exam slip when possible.
Pick Lens Materials For Power And Use
- Standard plastic suits low powers and casual wear.
- Thin high-index trims thickness for stronger powers.
- Polycarbonate or Trivex add impact resistance for kids and sports.
Coatings That Pay Off
Scratch resistance, anti-reflection, and smudge-resistant coatings keep vision crisp and cut glare. Photochromic tints help if you move between sun and shade all day. Blue-light marketing is noisy; pick it only if screen glare bothers you, not as a cure-all.
Progressives And Bifocals: Extra Checks
For multifocals, segment height and PD placement do the heavy lifting. That’s where a precise measurement keeps near fields from landing too high or too low. If you need a trusted primer on reading each Rx field, scan this clear breakdown from the American Academy of Ophthalmology. It matches the terms you’ll see on most exam printouts.
Troubleshooting: When New Glasses Don’t Feel Right
Give A Short Break-In Period
Fresh lenses, new axis angles, and different materials can feel odd for a few days. Wear them in safe settings first. If eyestrain or double vision appears, stop and get the order checked.
Compare The Ticket To Your Sheet
Ask the shop to print the final job ticket. Match OD/OS, SPH signs, CYL/AXIS pairs, ADD, prism values, and PDs line by line. Small typos cause big discomfort.
Frame Fit Matters
Slipping bridges, crooked temples, or high nose pads can shift the viewing zones away from your pupils. A quick adjustment often fixes blur that shows up only at certain angles.
FAQ-Free Quick Answers (No Fluff, Just Clarity)
Do I Always Need CYL And Axis?
No. If there’s no astigmatism correction, those boxes stay empty and the lab doesn’t use an axis.
Why Does My Rx Show Plus Cylinder At One Clinic And Minus Cylinder At Another?
Two writing styles describe the same optics. Labs can convert between styles. If you’re re-ordering, stick with the style on your sheet to reduce entry errors.
Can PD Be One Number Or Two?
Yes. One is binocular PD; two are monocular PDs. Enter what the site asks for. Multifocal orders often benefit from monocular PDs.
A Short Checklist Before You Click “Buy”
- Right line, right eye: OD matches right frame; OS matches left
- SPH signs are correct; minus for near-sighted, plus for far-sighted
- Any CYL has an Axis between 1–180 degrees
- ADD is present only for multifocals or readers
- Prism entries include base directions (BU/BD/BI/BO)
- PD matches your printout; monocular values entered when needed
- Frame width suits your PD and bridge
- Coatings and material match your power and lifestyle
Method Notes And Safe Use
This guide reflects standard optical terminology used by major eye-care organizations and retail labs. Always enter numbers exactly as written, including their signs and decimal points. If your sheet includes special notes from your doctor, keep them on the order so the lab can build the job as intended.