Education Centre › Spectacle Lenses
You’ve finished your eye test and have a small slip with two rows of numbers. You recognise your name, but SPH, CYL and AXIS don’t tell you much at first glance. Before choosing lenses, it helps to understand what each column is doing.
A spectacle prescription describes an optical correction. It is not a percentage score for your eyesight, a complete eye-health report or a shopping list of lens coatings. Read it as a set of related instructions, with the right and left eyes kept separate. This guide will help you follow the conversation with your optician without trying to change the prescription yourself.
Start with the eye and the purpose
Right eye may appear as R, RE or OD. Left eye may appear as L, LE or OS. Those labels refer to your eyes, not to the side of the paper as someone else looks at it. Check them before copying any numbers into a form.
Next, find out whether the prescription is for distance, near work or a particular task. Some slips show distance powers with a separate reading addition. Others print the full near prescription on another row. This distinction matters: adding a reading addition again to a row already labelled “near” would change the intended correction.
Keep the date and any written instructions visible. A cropped photograph containing only the numbers can leave out useful details. If the handwriting or layout is unclear, send the whole slip to the dispensing team and ask them to confirm it before ordering.
SPH: the spherical lens power
SPH means sphere. It gives the spherical component of the prescription, measured in dioptres, usually shown as D. A minus sphere is commonly used for short-sightedness; a plus sphere is commonly used for long-sightedness. The sign is part of the value, so +2.00 and −2.00 are not interchangeable.
PL, plano or 0.00 in the sphere column means zero spherical power. It does not automatically mean that no correction is needed: there may still be cylinder or another prescribed component on the same row.
Think of the columns together. If someone says, “My number is two,” that leaves several questions unanswered. Is it plus or minus? Which eye? Is there cylinder? Is that the distance power or a reading prescription? A clear copy of the prescription is more useful than a number remembered from the appointment.
CYL and axis: amount and orientation
CYL stands for cylinder, the component used to correct astigmatism. Astigmatism means the eye does not focus light evenly in different directions. Cylinder power is also measured in dioptres and may be written using either a plus or minus notation.
Axis specifies the orientation of that cylinder correction. It is written in degrees, generally from 1 to 180. An axis of 180 is not a stronger prescription than an axis of 90. They describe different orientations, not different amounts of correction.
CYL and axis belong together. If cylinder is prescribed but the axis cannot be read, do not choose a likely-looking value. Ask for clarification. When no cylinder correction is prescribed, the axis box is normally left unused. A blank box should not be filled with a made-up number just because an online form asks for one.
A useful question at the counter is, “Could you show me which part is the cylinder power and which is its axis?” That usually clears up the confusion faster than trying to compare the largest numbers on the slip.
ADD: extra power for a nearer task
ADD means addition. In an ordinary reading prescription, it is the extra plus power applied to the distance sphere for near work. It commonly appears when age-related changes in focusing make close tasks harder. There may also be a separate intermediate addition for a task such as computer work.
The ADD value is not necessarily the complete power of a reading lens. It has to be interpreted alongside the distance prescription and the way the slip is written. It also does not tell you which lens design to buy.
Reading glasses, bifocals and progressives meet different needs. If you want one pair for several distances, our guide to progressive lens viewing areas and fitting explains what to discuss. Tell the optician whether you mainly read books, use a desktop monitor or move between close work and distance viewing. The tasks matter as much as understanding the abbreviation.
A fictional prescription, read one row at a time
The following example is only for learning. It is not a recommended prescription or a way to estimate your own numbers.
Right eye: SPH −1.50, CYL −0.75, AXIS 90, ADD +1.25.
Left eye: SPH −1.00, CYL −0.50, AXIS 180, ADD +1.25.
For the right eye, −1.50 is the spherical component. The −0.75 cylinder is oriented at 90 degrees. The left eye has its own sphere, cylinder and orientation; its values should not be replaced with the right-eye values for convenience.
In this example, if those are distance values and +1.25 is the prescribed near addition, adding it to the right sphere gives −0.25 and to the left sphere gives +0.25. Cylinder and axis remain as specified in this simple illustration. This explains why buying ready-made +1.25 readers would not reproduce the full prescription.
Have the dispensing professional confirm the actual near prescription and intended working distance. The point of the example is to understand what “addition” means, not to convert your slip into a lens order without checking its instructions.
Other details you might see
PD means pupillary distance: the distance between the pupil centres, recorded in millimetres. It helps position lenses correctly in front of your eyes. It may be given as one total or separate measurements for each eye. Frame size printed on a spectacle arm is a different measurement and should not be substituted for PD.
Prism and base, when prescribed, provide additional instructions for how the lenses help the eyes work together. Keep both the amount and direction intact. If these fields appear on your slip, ask the optician to explain them rather than treating them as optional extras.
You may also see a vision result such as 6/6. That records performance on a vision test; it is not a lens power to enter under SPH. If a form seems to require a value that your prescription does not provide, pause and ask which information is missing.
Why two prescriptions can look different
Cylinder can be written in plus or minus form. Changing between the two involves changing the sphere and axis as well, and is called transposition. Two rows that look different can therefore describe the same optical correction.
Before concluding that your eyes have changed dramatically, ask the clinician or optician to compare both prescriptions in the same notation. Bring the original documents, including their dates. Do not compare only the SPH column or change the cylinder sign while leaving everything else untouched.
A spectacle prescription also should not be copied directly into a contact lens order. Lens position and fitting introduce other considerations. Read why contact lens and spectacle prescriptions differ before using a glasses slip to shop for contacts.
What the numbers do not choose for you
The prescription does not automatically select a frame, lens material or coating. Those decisions need a separate discussion about suitability, comfort, appearance and the activities you want the glasses for. A quotation should make clear which lens design, material and coatings are included.
If thickness is a concern, use the guide to high-index and thinner lens options to prepare questions. Ask the optician to explain the likely result in the frame you have selected, rather than choosing from the prescription number alone.
You can contact our team about prescription lenses and fitting with the complete slip and details of how you plan to use the glasses. There is no need to arrive knowing every abbreviation. A useful outcome is being able to explain what you are ordering and why it suits your daily tasks.
Frequently asked questions
Does a higher axis number mean worse eyesight?
No. Axis describes orientation, so it should not be ranked as mild or severe. Compare the complete prescription with professional help if you want to understand a change. A difference in axis alone does not tell you how well you will see.
Can I leave CYL out when ordering glasses?
Do not omit a prescribed component to simplify an order. If a seller cannot supply the prescription as written, ask what the limitation is and discuss suitable options with your optician. Choosing a convenient sphere value is not an equivalent replacement for the full prescription.
Does ADD mean I must buy progressive lenses?
No. It describes an additional correction, not a compulsory product. Ask about the practical differences between separate pairs and multifocal options for your routine. Your choice should account for the tasks you do and how comfortable you are switching glasses.
What if I cannot read a sign or decimal point?
Ask the prescriber or dispensing team for a clear copy. Do not guess from an old pair or another person’s prescription. Keep the original slip and let the professional confirm the ambiguous entry before lenses are made.
Sources: Association of Optometrists prescription guidance, New England College of Optometry prescription explanation and Specsavers guidance on prescription notation and measurements. This guide explains terminology and does not replace an individual examination or dispensing assessment.
