How to read an eye prescription: SPH, CYL, AXIS, ADD and PD meaning
To read an eye prescription, take each row as one eye (R/OD or L/OS) and each column as one part of the lens: SPH is the main power, CYL and AXIS correct astigmatism, ADD is extra power for reading and PD is the distance between the pupils. Once you know what each column means, you can read any prescription in seconds, spot mistakes before the lenses are ordered, and explain it to a customer in plain words.
This guide explains what the numbers on a prescription mean. It is not medical advice: for what a prescription means for your eyes, or whether it has changed, ask your optometrist or eye doctor.
Eye test results explained: a sample prescription
| Eye | SPH | CYL | AXIS | ADD |
|---|---|---|---|---|
| R (right, OD) | −1.25 | −0.50 | 90 | +2.00 |
| L (left, OS) | −1.00 | −0.75 | 85 | +2.00 |
Plus a PD of 62 mm. Some slips write the same thing on one line per eye, like R: −1.25 / −0.50 × 90, ADD +2.00. Here is what each of those numbers tells you.
R and L, OD, OS and OU
Prescriptions list the right eye first. Some doctors write OD (oculus dexter, right eye) and OS (oculus sinister, left eye), and OU means both eyes. Others simply write R and L, or RE and LE. "Right" always means the customer's right eye, not the side on your right as you face them.
Many Indian slips also have two rows per eye: DV (distance vision) and NV (near vision). The NV row is the reading power, already worked out. It does the same job as an ADD column.
Plus and minus signs: what they mean
| Sign | Means | In daily life |
|---|---|---|
| Minus (−) | Short sight (myopia) | Near things are clear; distant things such as road signs or the board at school are blurred. |
| Plus (+) | Long sight (hyperopia), or reading power | Near work can be tiring or blurred. Reading glasses and every ADD are plus. |
| 0.00, plano or PL | No power in that part | Common in one eye, or in the SPH when only astigmatism is corrected. |
The sign matters as much as the number. A missing minus sign turns a −2.00 lens into a +2.00 lens, which is a completely different pair of glasses.
What does SPH mean on an eye prescription?
SPH (sphere) is the main lens power, measured in dioptres (D) in steps of 0.25. A minus SPH means the person is short-sighted; a plus SPH means long-sighted. The bigger the number, the stronger the lens: −4.00 is a stronger lens than −1.00. If the box says 0.00, plano or PL, there is no spherical power for that eye. A prescription with SPH only and no CYL is sometimes written with DS (dioptre sphere), for example −1.25 DS.
What is CYL on an eye prescription?
CYL (cylinder) corrects astigmatism, where the eye focuses differently along different directions, so vision is stretched or blurred in one direction. CYL can be minus or plus depending on the doctor's convention. If there is no CYL, there is no astigmatism correction and AXIS will be blank. Some slips write DC (dioptre cylinder) after the number.
AXIS: the direction of the cylinder
AXIS tells the lab which direction the cylinder must be set. It is an angle from 1 to 180 degrees, with no degree sign needed: 90 is vertical and 180 is horizontal. AXIS is not a power, so a bigger number doesn't mean a stronger lens. A CYL value without an AXIS is an incomplete prescription: check with the doctor before ordering.
SPH, CYL and AXIS together
The three are always read together, in that order: SPH / CYL × AXIS. So −1.25 / −0.50 × 90 means a −1.25 main power, plus −0.50 of cylinder set at 90 degrees. When the values sit in columns, the × is left out.
ADD: near add, inter add and reading power
ADD (addition) is extra plus power for near work, usually written for customers over about 40 who find small print harder to read (presbyopia). It is always a plus number and is normally the same for both eyes. ADD is used for bifocal and progressive lenses, or added to the SPH for single-vision reading glasses.
- Near ADD (or just ADD): the extra power for reading at a normal reading distance. ADD +2.00 means 2 dioptres of extra plus power on top of the distance power.
- Inter ADD (intermediate add): a smaller extra power for arm's-length distance, such as a computer screen, a car dashboard or a billing counter. It is used for office or computer lenses and some progressive designs.
- ADD usually starts small in the mid-40s and increases with age, in steps of 0.25. The exact value is for the optometrist to decide.
Reading-glasses power = SPH + ADD. For the right eye above: −1.25 + 2.00 = +0.75 (with the same CYL and AXIS).
PD: pupillary distance
PD is the distance between the centres of the pupils, in millimetres. Adults are often somewhere between 54 and 74 mm. It can be written as one number (62) or as two monocular values (31/31), which is more accurate for progressive lenses. A wrong PD puts the optical centre of the lens in the wrong place and can cause eye strain, so measure it carefully if the prescription doesn't include it.
Other things you may see on the slip
- VA or vision (6/6, 6/9, N6): visual acuity, how clearly the eye sees on the chart. 6/6 is normal distance vision (the same as 20/20 in feet); N6 is small print read clearly up close. It describes the test, not the lens power.
- PRISM and BASE: a prism value (in prism dioptres) with a direction such as base in, out, up or down. It is used for some eye-muscle problems and must be passed to the lab exactly as written.
- Lens advice: some doctors add notes like "progressive", "bifocal", "ARC" or "constant use". Treat these as the doctor's advice for the lens, and see our guide to types of spectacle lenses.
Worked example: reading a sample prescription
| On the slip | What it says | In plain words |
|---|---|---|
| R SPH −1.25 | Right eye, minus 1.25 dioptres | Short sight in the right eye. |
| R CYL −0.50 AXIS 90 | Right eye cylinder at 90 degrees | A small amount of astigmatism; the lab sets the cylinder at 90 degrees (vertical). |
| L SPH −1.00 | Left eye, minus 1.00 dioptre | Slightly less short sight than the right eye. |
| L CYL −0.75 AXIS 85 | Left eye cylinder at 85 degrees | Slightly more astigmatism than the right eye. |
| ADD +2.00 | Extra reading power for both eyes | Needs help with near work; suits progressives, bifocals or a separate reading pair. |
| Reading power (R) | −1.25 + 2.00 = +0.75, −0.50 × 90 | The power a right-eye reading lens would have. |
| Reading power (L) | −1.00 + 2.00 = +1.00, −0.75 × 85 | The power a left-eye reading lens would have. |
| PD 62 | 62 mm between the pupils | Where the lab centres each lens. For progressives, ask for 31/31. |
Converting between minus and plus cylinder
Eye doctors and labs sometimes use different cylinder conventions. The same prescription can be written both ways (this is called transposition):
- New SPH = old SPH + old CYL.
- New CYL = old CYL with the sign changed.
- New AXIS = old AXIS ± 90, keeping the result between 1 and 180.
Example: +1.00 / −0.50 × 90 becomes +0.50 / +0.50 × 180. Both describe the same lens.
Glasses prescription vs contact lens prescription
They are not the same. A contact lens prescription also needs the lens brand, base curve and diameter, and for stronger powers (above about ±4.00) the power is adjusted because the lens sits on the eye instead of in front of it. Don't order contact lenses from a spectacle prescription alone; the optometrist should do a contact lens fitting.
Checks before you order lenses
- Right and left are not swapped.
- Every CYL has an AXIS, and every AXIS has a CYL.
- Signs are clear: a missing minus sign turns a −2.00 into a +2.00 lens.
- ADD is present if the customer wants bifocals or progressives.
- PD is recorded, ideally as two monocular values for progressives.
- The prescription is recent. If it is more than a year or two old, suggest a fresh eye test.
Keep every prescription on file
A customer's prescription history is the most useful record an optical shop has. It shows how their eyes are changing, lets you remake a pair without a new slip, and tells you when they are due for a test. In Opticdigit, SPH, CYL, AXIS, ADD and PD are entered on the bill itself and saved to the customer's profile, so the next visit starts with their full history. Read more in our guide to prescription management for optical shops, or see the plans for the best optical shop software in India.
Frequently asked questions
What does SPH CYL AXIS mean?
SPH (sphere) is the main lens power for short or long sight. CYL (cylinder) is the extra power that corrects astigmatism. AXIS is the angle, from 1 to 180, at which the cylinder power is set. All three are measured for each eye, and AXIS only appears when there is a CYL.
What does SPH mean on an eye prescription?
SPH stands for sphere, the main power of the lens in dioptres. A minus SPH (like −1.50) corrects short sight, where distant things look blurred. A plus SPH (like +1.50) corrects long sight. 0.00, plano or PL means no spherical power.
What is CYL on an eye prescription?
CYL stands for cylinder. It corrects astigmatism, where the eye focuses light differently in different directions. It can be written as a minus or a plus number, and it always comes with an AXIS that says which direction it is set in. A blank CYL means no astigmatism correction.
What does ADD +2.00 mean?
ADD +2.00 means 2 dioptres of extra plus power for reading, added on top of the distance power (SPH) of each eye. It is used for bifocal, progressive and reading glasses. For a distance SPH of −1.00, the reading power is −1.00 + 2.00 = +1.00.
What is the meaning of near add and inter add?
Near ADD is the extra plus power for reading at a normal reading distance. Inter ADD (intermediate add) is a smaller extra power for arm's-length work such as a computer screen or a shop counter. Both are added to the distance SPH. Your optometrist decides both values.
How do I read my eye test results?
Read each row as one eye (R or OD for right, L or OS for left) and each column as one part of the lens: SPH, CYL, AXIS, ADD. Minus means short sight, plus means long sight, CYL and AXIS mean astigmatism, and ADD means extra power for reading. For what the result means for your eyes, ask your optometrist.
Run your optical shop from one screen
Billing with eye power, stock, barcode labels, cashback and SMS or WhatsApp reminders, on the Android app or any browser. Plans from ₹2,500 a year.
Keep reading
FEATURES · 4 MINPrescription Management for Optical Shops: Never Lose a Customer's Eye Power Again
Save every customer's eye number (SPH, CYL, AXIS, ADD and PD) on the bill, track lens orders from lab to delivery, keep BP, sugar and IOL records, and send check-up reminders.
EYEWEAR BASICS · 3 MINTypes of spectacle lenses explained: single vision, bifocal, progressive and coatings
Types of spectacle lenses: single vision, bifocal, progressive; CR-39, polycarbonate, high-index; ARC, blue-cut and photochromic coatings explained.
EYEWEAR BASICS · 4 MINProgressive lens fitting height: how to measure, fit and explain progressives
Progressive lens fitting height is pupil centre to lens bottom, per eye, in the chosen frame. How to measure, PD, frames and why one number isn't enough.