After your eye test, you receive a piece of paper with a set of numbers, letters, and abbreviations that look nothing like anything from everyday life. Most patients either ignore it completely or type the numbers into an online lens calculator and hope for the best.
This guide explains every abbreviation on a standard Australian glasses prescription in plain English, so you can actually understand what your optometrist found.
OD and OS: Which Eye Is Which?
Prescriptions always list two eyes separately. The abbreviations come from Latin:
- OD (oculus dexter) = right eye
- OS (oculus sinister) = left eye
- OU (oculus uterque) = both eyes
Some prescriptions use R and L instead. The right eye is always listed first.
SPH (Sphere): Your Basic Prescription Strength
The sphere value tells you how much lens power is needed to correct your distance vision. It is measured in dioptres (D) and written in increments of 0.25.
- A minus sign (e.g. -2.50) means you are myopic (short-sighted). You can see clearly up close but not at distance.
- A plus sign (e.g. +1.75) means you are hyperopic (long-sighted). Your eyes have to work harder to focus at all distances, particularly up close.
- Plano (PL or 0.00) means no sphere correction is needed in that eye.
The larger the number (ignoring the sign), the stronger the prescription. A -5.00 is a stronger myopic prescription than a -1.50.
CYL (Cylinder) and Axis: Astigmatism Correction
If your prescription includes a CYL value, you have astigmatism. Astigmatism means the cornea or lens of your eye is not perfectly spherical, causing light to focus at two slightly different points rather than one. This results in blurring at all distances.
- CYL is the amount of astigmatism correction needed, also in dioptres. It can be written as a minus or plus value depending on the notation convention used.
- Axis is a number between 1 and 180, representing the angle in degrees at which the astigmatism correction must be oriented in the lens. Without the correct axis, the cylinder correction does not work.
If CYL is blank or 0.00, you do not have significant astigmatism in that eye.
Add: Your Reading Addition
The Add value appears on prescriptions for people who need bifocal or progressive (multifocal) lenses. It represents the additional magnifying power added to the lower portion of the lens to help with near vision (reading).
Add values are always positive and typically range from +0.75 to +3.50. They are usually the same for both eyes. If you have an Add value, it means your distance prescription alone is not sufficient for comfortable reading, which is normal from your mid-forties onwards as the lens inside the eye loses its flexibility (presbyopia).
PD: Pupillary Distance
PD stands for pupillary distance, the measurement in millimetres between the centres of your two pupils. This measurement is essential for placing the optical centres of the lenses directly in front of your pupils, which is where they must be for the prescription to work correctly.
PD is sometimes written as a single number (e.g. 64mm binocular) or as two numbers for each eye separately (e.g. 32/32 monocular). An incorrectly measured or applied PD is one of the most common reasons glasses cause headaches or feel uncomfortable, particularly progressive lenses.
Prism (if present)
Some prescriptions include a prism value, written with a base direction (e.g. 2 Base Out). Prism is prescribed when the two eyes do not align perfectly and need help pointing in the same direction. It is less common than sphere or cylinder correction. If your prescription includes prism, your optometrist will have explained why.
A Sample Prescription Explained
Here is an example to put it all together:
- OD: -3.25 / -0.75 x 175 / Add +2.00
- OS: -2.75 / -1.00 x 005 / Add +2.00
Reading this: the right eye needs -3.25 for distance myopia, with -0.75 of astigmatism correction at axis 175. The left eye needs -2.75 for myopia, with -1.00 of astigmatism at axis 5. Both eyes have a +2.00 reading addition, meaning progressive or bifocal lenses are appropriate.
How Long Is a Prescription Valid?
In Australia, a glasses prescription is generally valid for two years for adults and one year for children. After this period, an updated eye test is recommended before ordering new glasses, as your prescription may have changed. At Prime Optometrists Auburn, your eye test is bulk billed under Medicare.
If you have questions about your prescription or are unsure whether your current glasses are performing correctly, book an appointment online or call (02) 9761 0005.