Prescriptions and medicines
Eye prescription explained: SPH, CYL, axis, OD and OS
A glasses prescription is a small grid of abbreviations and plus or minus numbers, one row for each eye. Add yours below to see what each column means and what the numbers describe.
Explain your eye prescription
- 1. Add itDrop a PDF, take a photo or paste the text.
- 2. Check itPersonal details are removed on your device. You approve what is sent.
- 3. Read itSummary, table of results, terms and questions to ask.
The explainer opens on its own page with no adverts and no outside scripts. Your file is read on your device and is never uploaded.
What you get
- One row per eye with each value named.
- OD, OS and OU translated into right eye, left eye and both eyes.
- Sphere, cylinder, axis, add and prism explained.
- Questions to ask your optometrist.
Columns on a glasses prescription
- OD and OSRight eye and left eye (OU means both)
- SPH (sphere)The main lens power; minus for short-sightedness, plus for long-sightedness
- CYL (cylinder)Extra lens power to correct astigmatism
- AXISThe angle, from 0 to 180 degrees, at which the cylinder is set
- ADDAdditional power for near vision in reading or multifocal lenses
- PD (pupillary distance)The distance between the centres of your pupils, in millimetres
What this tool cannot tell you
MedicDecode explains what the columns and numbers stand for. It does not check that a prescription is right for you and cannot say anything about the health of your eyes. A glasses prescription is also not a contact lens prescription. If your vision changes suddenly, see an eye care professional.
Common questions
What do SPH, CYL and axis mean?
SPH (sphere) is the main lens power: minus for short-sightedness, plus for long-sightedness. CYL corrects astigmatism, and axis (0 to 180 degrees) gives the direction of that correction.
What do OD and OS mean on an eye prescription?
OD is the right eye and OS the left eye (from Latin). OU means both eyes.
Is there a bad axis for glasses?
No. Axis is only a direction, not a measure of how strong the prescription is. It matters only together with a CYL value.
Is a glasses prescription the same as a contact lens prescription?
No. Contact lens prescriptions include extra measurements such as base curve and diameter, and the powers can differ because the lens sits on the eye.
What does plano or PL mean?
It means zero: no lens power is needed in that position.
Why is one eye's number different from the other?
Each eye is measured separately, and it is common for the two to need different corrections.
Words you may see on this report
Tap a word for its plain-English meaning, an example line and what it does not mean.
- Adjunctive therapy
Adjunctive therapy is a medicine or treatment added to another main treatment to help it work better.
- Allergy alert
An allergy alert is a warning on an over-the-counter medicine label about allergic reactions the ingredient can cause, and what to do if one happens.
- BID, TID and QID
BID, TID and QID are abbreviations on prescriptions meaning twice a day, three times a day and four times a day.
- Bioequivalent
Bioequivalent means two versions of a medicine deliver the same active ingredient into the blood at about the same rate and amount.
- Boxed warning
A boxed warning is the strongest safety warning on a US medicine label, printed in a box, about a serious or life-threatening risk.
- Caplet
A caplet is a tablet shaped like a capsule: smooth, oblong and often coated, so it is easier to swallow. It is still a solid tablet.
- Contraindication
A contraindication is a reason not to use a particular medicine, test or procedure for a person because it could cause harm.
- Controlled substance
A controlled substance is a medicine or drug whose making, prescribing and supply are tightly regulated by law because it can be misused or cause dependence.
- Course of treatment
A course of treatment is the full planned period of taking a medicine, such as a set number of days of antibiotics.
- Excessive moisture
On a medicine label, 'protect from excessive moisture' is a storage instruction: keep the product dry so it does not break down or lose strength.
- Extended-Release
Extended-release means a medicine is designed to release its active ingredient slowly over many hours, so it is often taken less often.
- Fetal toxicity
Fetal toxicity means a medicine or substance can harm an unborn baby during pregnancy. Some medicine labels carry this warning in a box.