Decoding your eyeglass prescription: a plain-English guide
When you leave an optometrist's office in Sydney, Brisbane, or a smaller regional centre like Toowoomba, you usually walk away with a small piece of paper covered in numbers, letters, and mysterious abbreviations. Most patients tuck it into a wallet, photograph it for safekeeping, or hand it straight to a dispensing optician without ever really studying what it says. That is perfectly understandable, but a little literacy here can save you money, prevent headaches, and help you spot errors before they become a daily nuisance.
Australian prescriptions follow a fairly universal format, although a few local conventions exist around expiry, Medicare billing, and the way pupillary distance is recorded. Whether you collected your script from a clinic in Melbourne's CBD or a suburban practice in Adelaide, the core fields are almost always the same. Once you understand what each value represents, the document stops looking like a coded message and starts looking like a useful map of how your eyes actually focus light.
This guide walks through each component of a standard eyeglass prescription, explains the differences between single-vision, bifocal, and multifocal formats, and offers a few practical notes about how optical dispensing works under Australian standards. By the end, you should be able to read your own script with confidence, know which values matter most for which type of lens, and recognise when it is worth booking a follow-up rather than simply ordering online and hoping for the best.
| Term | Full Name | What It Measures | Typical Range |
|---|---|---|---|
| SPH | Sphere | Overall lens power for nearsighted or farsighted correction | -20.00 to +20.00 |
| CYL | Cylinder | Strength needed to correct astigmatism | -4.00 to +4.00 |
| AXIS | Axis | Orientation of the cylinder correction, measured in degrees | 1° to 180° |
| ADD | Addition | Extra power for reading or close work, layered on top of SPH | +0.75 to +3.50 |
| PD | Pupillary Distance | Distance between the centres of your pupils, used to centre the lenses | 54 mm to 72 mm |
| PRISM | Prism | Amount of base-in or base-out correction for eye-alignment issues | 0.5 to 10 prism dioptres |
Anatomy of a standard prescription
Most prescriptions, whether issued in Perth or Hobart, are laid out as two rows: one for the right eye and one for the left. The right eye is denoted OD, from the Latin oculus dexter, while the left is OS, oculus sinister. Some Australian practitioners now prefer to write RE and LE instead, which is a more accessible convention but means exactly the same thing. Each row lists the values from the table above as they apply to that individual eye, sometimes with extra symbols when special corrections are required.
You may also see OU on the form, which simply means "each eye" or "both eyes" together. It is occasionally used when the practitioner wants to indicate that the same value has been measured for both eyes, sparing the patient from comparing identical numbers side by side. Some modern scripts omit OU entirely and instead duplicate identical values across both the OD and OS rows, which is functionally the same outcome.
A few additional fields appear on more detailed scripts, including notes on lens material, coatings, and base curve. While not part of the prescription itself, these notes guide the optical lab that manufactures the lenses. If your script came from a practice that uses an in-house finishing lab, you may find that some of these technical notes are completed by the dispensing optician rather than the prescribing clinician, which is normal under Australian Optical Association guidance.
Sphere, cylinder, and axis: the core trio
The three values you will see on virtually every prescription are SPH, CYL, and AXIS, and they work together to compensate for the two most common focusing errors: spherical blur and astigmatism. A spherical blur is what most people think of as being short-sighted or long-sighted. If the SPH figure carries a minus sign, your eye focuses light in front of the retina, which makes distant objects appear blurry. A plus sign means the opposite: light focuses behind the retina, and close objects struggle to come into sharp focus. The bigger the number, the stronger the correction required.
The CYL and AXIS values handle astigmatism, which is when the cornea or lens is shaped less like a basketball and more like a rugby ball. The cylinder value tells the lab how much extra correction is needed in one specific direction, and the axis value tells it where to place that correction. The axis is measured in degrees from 1 to 180, with 90 being straight up and down. If your CYL reads -1.25 and your AXIS reads 180, for example, the lab knows to add a small amount of cylindrical power along the horizontal meridian of the lens.
In Australia, these measurements are usually taken after a comprehensive eye exam that may attract a Medicare rebate under the Medicare Benefits Schedule, provided the provider is a registered optometrist. The exact rebate amount varies from year to year, but for most adults the out-of-pocket cost of the exam itself is modest. That affordability makes it practical to refresh your script every couple of years rather than stretching a single pair of glasses indefinitely, particularly if you spend long hours working under fluorescent office lighting or staring at a screen.
Reading prescriptions: ADD power explained
Once you cross your mid-forties, almost everyone develops some degree of presbyopia, which is the gradual stiffening of the eye's internal crystalline lens. Reading glasses, bifocals, and progressive lenses all address this with an ADD power, an additional amount of plus correction that is layered on top of your distance prescription. On a script you will usually see ADD written once, because the value typically applies equally to both eyes.
The ADD value generally falls between +0.75 and +3.50 dioptres, and it tends to increase gradually over the years. A +1.00 add at age forty-five might become a +2.00 add by fifty-five, eventually settling somewhere around +2.50 to +3.00 in later life. If you see only the standard distance values on your prescription, that generally indicates a single-vision correction, either for distance only or for reading only. If you see ADD alongside SPH, CYL, and AXIS, you are looking at a multifocal script and will need lenses designed to accommodate both near and far vision in the same pair.
In an Australian context, many people who work long hours on screens in offices from Canberra to Parramatta ask about "intermediate" ADD values, which sit somewhere between the full reading add and zero. These are particularly common in occupational lenses or computer-specific pairs. If your script does not list an intermediate value but you spend most of your day at a desk, ask your dispensing optician whether a slightly reduced ADD can be ordered, or whether a separate pair of computer glasses would be more comfortable for sustained close work.
Pupillary distance and other key measurements
Pupillary distance, almost always abbreviated as PD, is the distance in millimetres between the centres of your pupils. It is essential because lenses must be positioned so that their optical centres line up with your pupils. A PD that is off by even a few millimetres can cause eye strain, headaches, and that odd "swimming" feeling some people notice when they first put on a new pair of glasses, especially during driving or walking down a busy street.
Not every Australian optometrist writes the PD directly onto the prescription, partly for historical reasons and partly because it is a measurement that can shift over time, particularly in growing children. Many practices record a single binocular PD, such as 64 mm, while others split it into two monocular values, one for each eye, often separated by a slash. Single PDs are easier to use, but monocular PDs allow more precise lens placement, especially for progressive or prism prescriptions, where a millimetre here or there can change the experience considerably.
You may also see other measurements on more detailed scripts, such as SEG height (the vertical position of a bifocal segment), OC height (optical centre height), or a near PD measured specifically for reading. These values become important when dispensing multifocal lenses, where a few millimetres can determine whether you can comfortably read a menu in a Perth café or find yourself tilting your head awkwardly all evening just to find the sweet spot in the lens.
Prism, base direction, and special notations
A small number of prescriptions include a prism value, which is used when the eyes do not align perfectly. Prism lenses shift the image slightly so that the brain can fuse the two retinal images into one. You will see a number followed by a direction, such as "1.5 BO" for one and a half prism dioptres base-out, or "0.5 BU" for base-up. Prism corrections are relatively uncommon, but they are essential for people with strabismus, certain types of diplopia, or post-stroke visual changes.
The base direction matters as much as the strength itself. A base-out prism pulls the image towards the outer edge of the lens, while a base-in prism pulls it towards the nose. Misreading "BI" as "BO" can result in lenses that make double vision worse rather than better, which is one of the reasons prism scripts are usually dispensed in person rather than shipped from an online warehouse based overseas. The Optometry Board of Australia recommends that complex prescriptions involving prism be handled by a qualified dispenser who can verify the lens centration before the patient leaves the practice.
You might also spot notations such as "PL" or "plano", meaning zero power, often written for one eye if it does not need correction. "Balance" indicates a lens used to match the weight and thickness of the other side, even when no optical correction is required. These small additions ensure that a pair of glasses sits evenly on the face and looks symmetrical through the lenses, particularly important for stronger prescriptions where lens thickness can vary noticeably between the two eyes.
Common questions about Australian prescriptions
One of the most frequent questions is how long a script remains usable, and the answer varies slightly by state and by retailer. Most Australian optical dispensers accept a prescription that is less than two years old for general glasses, and less than twelve months old for contact lens fittings. These are not strict legal limits but rather professional guidelines from the Optometry Board of Australia, designed to ensure your correction still matches your current vision rather than an outdated snapshot. Children and people with rapidly changing conditions such as diabetes usually need more frequent reviews.
Another common point of confusion is whether you must order your glasses from the practice that issued the prescription. The short answer is no. Australian regulations recognise a patient's right to take their script elsewhere, whether that is a chain retailer in Brisbane's Queen Street Mall, a boutique independent in Newtown, or an online supplier. However, having the original optometrist involved in dispensing often makes it easier to resolve any fitting issues, and complex prescriptions involving prism or progressive lenses are usually best handled face-to-face. If you would like a fuller picture of what a comprehensive eye exam should cover, you can review the services offered by Kramer Family Eyecare at https://drandrewkramer.com/services to see how a thorough workup is structured.
A final practical tip: keep a clear photograph of your current prescription on your phone. If you ever lose or break your glasses while travelling between, say, Sydney and a coastal town like Byron Bay, you will be able to order a replacement or arrange an emergency dispense without delay. Most practices are happy to email a copy on request, and a sharp photograph under good lighting is usually readable enough for a dispensing optician to work from, even at short notice.
Most optical dispensers across Australia will spend a few minutes explaining your script in plain language at no charge, and there is no obligation to buy on the spot. If a figure on your script looks unusual or has shifted noticeably since your previous visit, that is a useful detail to mention when you book your next exam, since it may point to a need for additional testing such as corneal topography or retinal imaging. Bringing along your current glasses and any older prescriptions you still have at home can also help the optometrist see how your correction has changed over time. If anything on your script does not make sense after working through this guide, ring the practice that issued it, ask them to walk you through the numbers line by line, and book a fresh exam if it has been more than two years since your last one.