How to Read Your Prescription
A spectacle prescription looks like a code, and it very nearly is. There are only five numbers that matter for most people. Here is what each one means.
If you would rather not work it out, bring the prescription into any of our studios and we will read it for you and explain what it means for the frames you are looking at.
The layout
A prescription has two rows, one per eye. OD or RE is your right eye — oculus dexter. OS or LE is your left. OU means both. The right eye is conventionally written first.
The columns are usually SPH, CYL, AXIS and ADD, with your PD somewhere at the bottom.
SPH — sphere
The main strength of the lens, measured in dioptres, almost always in steps of 0.25.
- A minus number (−2.00) corrects short sight, or myopia: distance is blurred, close work is clear.
- A plus number (+2.00) corrects long sight, or hypermetropia.
- 0.00, Plano, PL or an empty box means no spherical correction is needed for that eye.
The further from zero the number is, the stronger the lens — and the more the choice of frame matters, which is why we would rather see the prescription before you settle on one.
CYL — cylinder
The amount of astigmatism correction. Astigmatism simply means the front of the eye is shaped a little more like a rugby ball than a football, so it focuses at different strengths in different directions.
A blank box, 0.00, or DS (dioptres sphere) means no astigmatism correction. Like the sphere, it is written in dioptres and can appear as a plus or a minus figure. The same lens can be written either way round — add the cylinder to the sphere, flip the cylinder's sign, and turn the axis by 90 degrees, and you have the same prescription in the other notation. Practices differ in which form they use, so do not be alarmed if a new prescription looks nothing like the old one.
AXIS
A number between 1 and 180, often written after a small x — for example −0.75 x 180.
It is a direction, not a strength. It tells the lab at what angle to set the cylinder. Axis 180 is not stronger than axis 10, it is simply oriented differently. An axis only means something when there is a cylinder to go with it.
ADD — addition
Extra plus power for close work, added to the distance prescription in the lower part of a bifocal or varifocal, or used on its own for reading glasses. It is always a plus figure, usually the same for both eyes, and commonly between +0.75 and +3.50. It tends to grow with age.
If your sheet has an ADD, your lens options need thought: varifocals need enough depth in the lens to hold the reading portion, so a very shallow frame is a poor choice. We will tell you if a frame you like will fight your prescription.
PD — pupillary distance
The distance between the centres of your pupils, in millimetres. Most adults fall between about 54 and 70.
It may be one number (both eyes together, say 63), or two (say 32 / 31), which is more precise because faces are rarely symmetrical. A separate, slightly smaller near PD is sometimes given for reading.
PD is how the lab centres the optical middle of each lens in front of each pupil. Get it wrong and the glasses can pull, strain or give headaches even though every other number is right. PD is often left off a prescription — it is a dispensing measurement rather than a clinical one. We can measure it for you in the shop.
Things you may also see
- PRISM and BASE — a prism shifts the image slightly to help the two eyes work together. It is measured in prism dioptres, with a base direction: up, down, in or out (BU, BD, BI, BO).
- BAL or Balance — a lens made to match the weight and appearance of the other one, where an eye has no useful sight.
- V/A or VA — visual acuity, how well you read the chart. Nothing to do with the lens itself.
- A date — more important than it looks. See below.
A worked example
OD −2.25 / −0.75 x 180. OS −2.00 / −0.50 x 175. ADD +1.50. PD 63.
Read that as: both eyes are moderately short-sighted, the right a little more than the left. Each has a small amount of astigmatism, corrected at close to the horizontal. There is a reading addition of +1.50, so this person is in varifocals, bifocals or a separate pair for close work. The lenses will be centred 63 mm apart.
How old is too old
A prescription more than a year old should be re-tested before new lenses are made to it. Eyes change, and there is no sense paying for lenses that are already out of date. Eye testing is done in store — mention it when you ring, and see Book a Fitting.
A contact lens prescription is not the same thing
Contact lens prescriptions include a base curve and a diameter, and the powers differ from spectacle powers because the lens sits on the eye rather than in front of it. The two are not interchangeable. Use your spectacle prescription to order glasses.
Before you order
Check the values against your sheet carefully — sphere, cylinder, axis, addition, and which row is which eye. Lenses are cut to your prescription alone and cannot be resold, so they are not returnable on a change of mind, only for a fault; the detail is in Cancellation & Returns and the Terms of Service. How we store a prescription you send us is set out in the Privacy Policy.
If any of it is unclear, bring it in or send us a photograph. We would much rather answer a question first than remake a lens afterwards.
Contact
Phone and WhatsApp: +91 75750 01691
Email: contact@chashmish.com