What do the letters on my prescription mean?
Your prescription lists the lens power your eyes need, one row for each eye. The key terms are SPH, CYL, AXIS, ADD and PD. Once you know them, the slip stops looking like code.
Which terms should I know?
| Term | Meaning |
|---|---|
| OD | Right eye (sometimes written R) |
| OS | Left eye (sometimes written L) |
| SPH | Sphere, the main lens power |
| CYL | Cylinder, extra power for astigmatism |
| AXIS | The angle, from 1 to 180, at which the cylinder power sits |
| ADD | Extra power added for near work, such as reading |
| PD | Pupillary distance, the gap between your pupils in millimetres |
What is SPH?
SPH is the main power of the lens. A minus number (for example -2.00) generally means the lens helps you see distant things clearly. A plus number (for example +1.50) generally helps with near vision. The bigger the number, the stronger the lens.
What are CYL and AXIS?
CYL is extra power needed when the eye is shaped a little like a rugby ball and not a football, which is called astigmatism. It is always paired with AXIS, which tells the lab at which angle to place that power. If CYL is blank or shows DS or SPH only, there is no cylinder in the prescription.
What is ADD?
ADD is extra power for near tasks like reading. You will usually see it on prescriptions for bifocal or progressive lenses, and sometimes for reading glasses.
What is PD?
PD is the distance between the centres of your pupils. It helps position the lens centres in front of your eyes. It matters for comfort and clarity, so it is measured and checked when you order glasses.
A worked example
Here is an example with made-up numbers, only to show how to read a slip. It is not anyone’s real prescription.
| Eye | SPH | CYL | AXIS | ADD |
|---|---|---|---|---|
| OD (right) | -2.00 | -0.50 | 90 | +1.50 |
| OS (left) | -1.75 | -0.25 | 85 | +1.50 |
PD: 62 mm
How to read it:
- The right eye needs a -2.00 lens power for distance.
- It also has a small cylinder of -0.50 placed at an angle of 90.
- The left eye is similar, with -1.75 and a smaller cylinder.
- Both eyes have an ADD of +1.50, so this person may be given bifocal or progressive lenses for near work.
- The PD of 62 mm tells the lab how far apart to centre the lenses.
The two eyes often have slightly different numbers. This is very common.
Should I ask questions?
Always. If any number on your slip is unclear, ask the optometrist to explain it. Do not try to guess whether the numbers are good or bad, since only an eye test tells you what you need.
Why does the date matter?
Your eyes can change, and a prescription is a snapshot of one day. A general guide is to test every one to two years, or sooner if your vision feels different.
If you notice sudden changes in vision, eye pain, redness or flashes of light, see an eye doctor without waiting.
Visit Optimax Vision in Super Mall 1, Infocity (open 11 am to 9 pm every day) or WhatsApp +91 70165 09225.
Quick questions
What do OD and OS mean?
OD stands for the right eye and OS for the left eye. Some prescriptions simply write R and L instead.
What does a minus or plus sign mean?
A minus sign usually shows lenses that help with distance vision, and a plus sign shows lenses that help with near vision. The number shows how strong the power is.
Can I use my prescription at any shop?
Usually yes, but a prescription is best used while it is still recent. If it is old or your vision has changed, get a fresh eye test.