How to read your eyeglass prescription
SPH is your main power (minus for distance, plus for near). CYL and AXIS describe astigmatism, the amount and the direction. ADD is the extra reading power for people over 40. PD is the distance between your pupils in millimetres, which we need to centre the lenses. OD is your right eye, OS your left.
Most people fold their eyeglass prescription, put it in a wallet, and hand it over without reading it. That is fine. But if you have ever ordered glasses online and wondered which box to type which number into, this is the page to keep open.
Here is a real-looking slip from our shop, then each column explained.
| SPH | CYL | AXIS | ADD | |
|---|---|---|---|---|
| OD (right) | -2.25 | -0.50 | 180 | +1.50 |
| OS (left) | -2.00 | +1.50 |
PD: 63 mm
OD and OS: right and left
OD is the right eye, OS the left. The letters come from Latin and every optician in Nepal still uses them. Some hospital slips write R and L. If you see OU, that means both eyes together.
The eyes are almost never identical. In our example the right eye needs a bit more power than the left. That is normal.
SPH: the main power
Sphere is the number that does most of the work. A minus sign means you are short-sighted: distance is blurry, near is fine. A plus sign means long-sighted: near is the struggle. The bigger the number, the stronger the lens.
The numbers move in steps of 0.25. A minus 0.50 is barely there. A minus 2.25, like our example, means the bus number across the road is a smudge without glasses. Above minus 4.00 we start talking about thinner lens materials, because a standard lens gets thick at the edges.
CYL and AXIS: astigmatism
If your cornea is shaped more like a rugby ball than a football, light focuses unevenly. That is astigmatism, and it needs two numbers to correct.
CYL (cylinder) is how much. AXIS is the direction, from 1 to 180 degrees. In the example, the right eye has minus 0.50 of cylinder at 180 degrees. The left eye has none, so both boxes are empty.
One rule: a CYL without an AXIS is a mistake on the slip. If you see one without the other, ask before ordering.
ADD: reading power
ADD only appears when the eye needs help up close, which for most people begins somewhere after 40. It is always a plus number and it is added on top of the SPH for the reading part of the lens. A plus 1.50 ADD is typical for someone in their late forties.
If you have an ADD, you have three lens choices: separate reading glasses, bifocals, or a progressive. The price difference between those is in our post on what glasses cost in Nepal.
PD: the number most slips forget
Pupillary distance is the gap between the centres of your pupils in millimetres. Adults are usually between 58 and 68 mm. We need it to put the optical centre of each lens exactly in front of each eye. Get it wrong by a few millimetres and the glasses feel slightly off all day, even when the powers are right.
Many slips from other shops leave PD out. If yours does, do not guess. We measure it in the shop for free, or you can follow our guide on measuring pupillary distance at home with a ruler and a mirror.
Things that are not on the slip but matter
The date. A prescription is reliable for about two years. Eyes drift, and a lens cut to an old power can cause the headaches people blame on screens.
The lens type. The slip tells us the power, not whether you want single vision, blue coat, or progressive. That is a conversation, and it is where the free test at the showroom earns its keep.
The frame size. A strong prescription in a very large frame gets thick and heavy at the edges. We will steer you toward a frame the lens suits, like the Premium Rectangle Frame at NPR 1,200, which carries most powers without complaint.
What to do with it
Reading an eyeglass prescription from a Nepali hospital
Slips from Tilganga, Bir Hospital or a district eye camp look different from ours but carry the same numbers. A few things to know.
Hospital slips often write the power in a grid with R and L rather than OD and OS, and some abbreviate sphere as "Sph" and cylinder as "Cyl". The numbers mean exactly what this guide says. Many camp slips leave out the PD entirely, and a few leave out the AXIS when there is a CYL, which is the one thing that has to be sent back for correction.
People also ask whether a "chasma ko power" from one shop can be used at another. It can. A prescription is a measurement of your eyes, not a product of the shop. Bring the slip, we verify it in a minute on the refractor, and we cut lenses to it.
One more habit worth keeping: photograph every slip. Prescriptions get lost between the hospital and the shop, and a photo on your phone is enough for us to make your lenses.
Take a photo of the slip and keep it on your phone. When you order online, type the numbers exactly as written, signs included. If anything is missing or looks odd, message us the photo before paying. We would rather fix a slip than remake a lens.
If your slip is missing the PD or the AXIS, bring it to either showroom. We check it on the refractor during the free eye test and fill in whatever is missing.
Frequently asked
- My slip says OD and OS. Which is which?
- OD is the right eye, OS the left. Some slips write R and L instead. OU means both eyes.
- There is nothing in the CYL column. Is that a mistake?
- No. A blank or 0.00 means no astigmatism in that eye, and the AXIS column will be blank too.
- Can I use a prescription from another shop or a hospital at Blurkart?
- Yes. Bring it in or send a photo with your order. If the PD is missing we measure it for free.
- How old can my prescription be?
- Around two years for adults. Children and anyone with diabetes should retest yearly. The test is free at our showrooms.
- Chasma ko power kasari padhne?
- Look at the SPH column first: minus means short-sighted, plus means long-sighted. CYL and AXIS together describe astigmatism. ADD is reading power for people over 40. PD is the distance between your pupils. Send us a photo of the slip if anything is unclear.