Your glasses, explained
Understanding your glasses prescription in Reservoir
Those letters and numbers describe how your lenses help you see. Here is a plain-English guide to reading the form and asking useful questions at your next visit.
Bring your prescription and current glasses to Reservoir Spectacles. We can talk through what they mean for reading, screens and distance vision.
Start with the labels
What do SPH, CYL, AXIS and ADD mean?
Each eye has its own entry. R, RE or OD means right eye; L, LE or OS means left eye. You may also see separate distance and near sections.
| Term | What it tells you |
|---|---|
| SPH (sphere) | The spherical lens power. A minus sign commonly corrects short-sightedness; a plus sign commonly corrects long-sightedness. Power is measured in dioptres. |
| CYL (cylinder) | The amount of correction for astigmatism. This field may be blank when no cylinder correction is prescribed. |
| AXIS | The angle of the cylinder correction, written in degrees. It describes orientation, not how strong the prescription is. |
| ADD | Extra focusing power for near tasks, added to the distance prescription when needed. It is not your complete reading prescription on its own. |
| PRISM / BASE | Prism correction and its direction, when prescribed to help the eyes work together. These fields are often blank. |
Terminology references: Cambridge University Hospitals and Bupa Optical Australia.
Three useful distinctions
The form makes more sense when you read it as a whole.
Keep the plus or minus sign
The sign is part of the prescription. “Plano” or 0.00 means no spherical power in that field; another field may still contain a correction.
An axis is an angle
An axis of 180 is not a stronger correction than an axis of 90. The cylinder amount and its axis need to be read together.
ADD is only one part
A near addition needs the rest of your prescription for context. Ask which reading-glasses options suit your usual tasks and working distances.
If two prescriptions look different, bring both rather than trying to combine the numbers yourself. Different notation and the purpose of each pair can make comparison confusing.
From prescription to comfortable glasses
Why do fitting measurements matter?
PD and lens position
Pupillary distance (PD) describes the spacing of your pupils. It is one of the measurements used when fitting glasses. The prescription describes the lens correction; fitting measurements help position it in front of your eyes.
The frame is part of the fitting
Fitting heights and the way a frame sits also matter, particularly for multifocals. Bring the frame you intend to use so we can assess the fit alongside your lens options.
See our guide to frame fit and comfort. Further reading: College of Optometrists guidance on PD.
Questions to bring with you
Make your next visit useful.
What should I ask about my prescription?
Ask what each pair is intended for, when to wear it, what has changed and when your eyes should next be checked. Tell us about your screen setup, reading distance and the tasks that feel difficult.
Does this form tell me everything about my eyes?
It records the prescribed optical correction. It does not replace the eye-health assessment or the advice given during a comprehensive eye test. Bring questions about your results as well as the numbers.
What if I want contact lenses instead?
Tell us before ordering. Contact lens fitting involves assessing lenses on your eyes; your glasses form alone does not establish which contact lens is suitable.
Do not assume new vision problems simply mean you need stronger glasses. Seek prompt assessment for a change in vision. Severe eye pain, flashing lights or an eye injury may need urgent care; if we are closed or unavailable, contact an urgent eye service or an emergency department. Read our urgent eye-care guidance.
General information checked 24 September 2026. Urgent-care advice: Healthdirect Australia. Your optometrist can explain your individual results.
Reservoir Spectacles
Let’s make your prescription easier to understand.
Bring your current glasses and any prescription you would like explained. Find us at 2C Edwardes Street, Reservoir.