- Home: eye surgery in Istanbul
- Free eye tools
- Eye prescription reader
Online Eye Prescription Reader: Understand Sphere, Cylinder and Axis
Before you start: have your latest prescription in front of you. It is the one your optician or eye doctor gave you after your last sight test, not the label on a box of lenses.
Use this free online eye prescription reader to see what your glasses prescription means. Each eye has a sphere (SPH) for short or long sight, a cylinder (CYL) and axis for astigmatism, and sometimes an ADD for reading, all in dioptres (D): minus means short-sighted, plus long-sighted. Want to be free of glasses? Prof. Dr. Ahmet Satıcı or Op. Dr. Aysan Bayram can tell you whether laser or lens surgery fits.
Before you start: have your latest prescription in front of you. It is the one your optician or eye doctor gave you after your last sight test, not the label on a box of lenses.
How to read your eye prescription (UK and US): SPH, CYL, AXIS and ADD
Your prescription has one row per eye. The American Academy of Ophthalmology (AAO) explains the columns.
| Column | What it tells you | How to read it |
|---|---|---|
| OD / OS | Right eye and left eye | Some practices write RE and LE; OU means both |
| SPH (sphere) | The main lens power | Minus means short-sighted, plus long-sighted |
| CYL (cylinder) | Extra power for astigmatism | Empty or 0 means none |
| AXIS | Direction of the astigmatism | A whole number from 1 to 180 degrees |
| ADD | Extra power for near work | Reading glasses, bifocals, varifocals |
| Prism | Correction for double vision | Measured in prism dioptres, with a base direction |
Example: −2.00 −0.75 × 180 means 2 dioptres of short sight and 0.75 dioptres of astigmatism along the 180° (horizontal) line.
What is a dioptre (diopter)?
A dioptre (D; Americans write diopter) is the unit of lens power: one divided by the focal length in metres. Prescriptions go up in steps of 0.25 D.
What does SPH (sphere) mean on an eye prescription?
SPH is the main lens power. A minus number corrects short sight (myopia), where distant objects look blurred. A plus number corrects long sight (hyperopia), where near objects are harder to see. "Plano" means no sphere power. Your spherical equivalent is the sphere plus half the cylinder: −2.00 with −1.00 of cylinder is −2.50 D.
What do cylinder (CYL) and axis mean?
CYL corrects astigmatism, where the eye is shaped more like a rugby ball than a football, so light focuses in more than one place (NHS). The axis says in which direction the cylinder acts: 90 is vertical, 180 horizontal. The AAO says most people have 0.5 to 0.75 D of astigmatism, and 1.5 D or more typically needs correction.
Some practices write the cylinder with a plus sign, others with a minus; both describe the same lens. To switch, add sphere and cylinder, flip the cylinder's sign and add 90 to the axis (subtract 180 if it passes 180). So −2.00 −1.00 × 180 equals −3.00 +1.00 × 90. The reader shows both.
What do ADD, PD, prism and BVD mean?
ADD is the near addition for presbyopia, which the AAO says typically becomes noticeable shortly after 40; your near power is sphere plus ADD. PD is the distance between your pupil centres. BVD, back vertex distance, is the gap between the back of the lens and the cornea, normally 12 to 14 mm. It matters above about ±4.00 D, because moving the lens changes the power reaching your eye, which is also why contact-lens prescriptions differ from glasses.
Is a 1.50 eye prescription bad?
No. A prescription measures the lens you need, not the health of your eyes. A sphere of −1.50 is low myopia: the international definition counts −0.50 D to just above −6.00 D as low, and −6.00 D or stronger as high, which carries a higher risk of retinal problems (EyeWiki, AAO). A cylinder of 1.50 is where the AAO says astigmatism typically needs correction.
Can you get an online eye prescription?
Not from a reader like this: it explains a prescription but cannot create one. The AAO says online vision tests can measure prescription power for healthy adults aged 18 to 39 with mild to moderate prescriptions and no symptoms, but cannot detect eye disease with hidden symptoms, suit neither high-power nor irregular prescriptions, and must never be used to order contact lenses. Prescriptions must be approved by an optometrist or ophthalmologist. In the UK, eligible people can have a free NHS sight test every two years. To convert 6/6 or 20/20, use our visual acuity converter.
Which prescriptions can laser or lens surgery treat?
The Royal College of Ophthalmologists (RCOphth) says laser suits people over 18 whose prescription has changed by no more than 0.5 D in two years and falls within these ranges; higher ones usually need a lens-based option.
| Correction | Typical range |
|---|---|
| Laser: short sight | Up to −10.00 D |
| Laser: long sight | Up to +4.00 D |
| Laser: astigmatism | Up to ±6.00 D |
| ICL (FDA range): myopia / toric cylinder | −3.00 to −20.00 D / 1.00 to 4.00 D |
Read about myopia (short-sightedness) treatment or laser eye surgery in Turkey. Your surgeon decides after scans of your cornea, lens and retina.
This reader explains the numbers on a glasses prescription. It does not measure your eyes, diagnose any condition or show whether you are suitable for treatment. Only an optometrist or ophthalmologist can examine you and prescribe. If your vision changes suddenly, see an eye doctor.
Try our other free eye tools
Take the astigmatism test, the lens finder quiz, the colour blindness test or the Amsler grid test, or explore the eye colour chart and inheritance calculator.
Prof. Dr. Ahmet Satıcı (laser, ICL and lens exchange) and Op. Dr. Aysan Bayram (laser) treat short sight, long sight and astigmatism in a fully equipped, Ministry of Health–licensed operating theatre in Istanbul.
Eye prescription: frequently asked questions
SPH is the sphere, the main lens power in dioptres. Minus corrects short sight; plus corrects long sight.
CYL is the cylinder, the extra power that corrects astigmatism. It always comes with an axis.
The axis, from 1 to 180 degrees, is the direction of the astigmatism. It is only used with a cylinder.
BVD is back vertex distance, the gap between lens and eye, normally 12 to 14 mm. It matters mostly above about ±4.00 D.
No. A contact-lens prescription is different because the lens sits on the eye, and the AAO says never to order contacts from a home vision test.
It gives a first indication: the RCOphth says laser most likely suits up to −10.00 D, +4.00 D and ±6.00 D of astigmatism. Your surgeon must also check your corneas and eye health.
Sources for the facts on this page
- OD/OS, sphere (minus = short-sighted, plus = long-sighted, "−9.00 D" example), cylinder, axis (1–180), add, prism (double vision), contact-lens prescription differs from glasses: American Academy of Ophthalmology, "How to Read Your Eyeglasses Prescription" https://www.aao.org/eye-health/glasses-contacts/how-to-read-eyeglasses-prescription
- Astigmatism: most people have 0.5–0.75 D, 1.5 D or more typically needs correction; can change over time: AAO, "What Is Astigmatism?" https://www.aao.org/eye-health/diseases/what-is-astigmatism
- Astigmatism = "rugby ball" shape, light focused at more than one place; short-sightedness and long-sightedness definitions; laser and lens surgery not available on the NHS: NHS, "Astigmatism" https://www.nhs.uk/conditions/astigmatism/ · "Short-sightedness (myopia)" https://www.nhs.uk/conditions/short-sightedness/ · "Long-sightedness (hyperopia)" https://www.nhs.uk/conditions/long-sightedness/
- Presbyopia becomes noticeable shortly after age 40: AAO, "What Is Presbyopia?" https://www.aao.org/eye-health/diseases/what-is-presbyopia
- Online vision tests: healthy adults 18–39, mild to moderate prescriptions; cannot detect hidden disease; not for high-power or irregular prescriptions; never for contacts; prescriptions approved by an optometrist or ophthalmologist; exams every 5–10 years at 18–39: AAO, "Using a home vision test to order glasses online" https://www.aao.org/eye-health/tips-prevention/self-home-vision-test-order-glasses-online
- Keeping spherical equivalent constant when changing cylinder (+0.50 D cylinder with −0.25 D sphere); axis scale 1–180: AAO, "Refraction 101: Go Forth and Refract" https://www.aao.org/young-ophthalmologists/yo-info/article/refraction-101-go-forth-and-refract
- Myopia ≤ −0.50 D spherical equivalent; low myopia down to just above −6.00 D; high myopia ≤ −6.00 D; spherical-equivalent definition: Flitcroft DI, et al., "IMI – Defining and Classifying Myopia", Invest Ophthalmol Vis Sci 2019;60:M20–M30 https://pmc.ncbi.nlm.nih.gov/articles/PMC6735818
- High myopia ≥ −6.00 D; complications (retinal detachment, myopic maculopathy, macular holes); yearly review when stable: EyeWiki (AAO), "Pathologic Myopia (Myopic Degeneration)" https://eyewiki.org/Pathologic_Myopia_(Myopic_Degeneration)
- With-the-rule (steepest vertical, axis about 90 in plus-cylinder terms) and against-the-rule (steepest horizontal, about 180; most common in adults over 40): EyeWiki (AAO), "Physiology of Astigmatism" https://eyewiki.org/Physiology_of_Astigmatism
- Anisometropia (≥ 1.0 D difference between eyes) in 17.9% of 134,603 refractive-surgery candidates: Deuchert et al., PLoS One 2025 https://pmc.ncbi.nlm.nih.gov/articles/PMC11698341/
- EVO ICL FDA range: myopia −3.0 to −20.0 D; toric cylinder 1.0–4.0 D: EyeWiki (AAO), "Implantable Collamer Lens" https://eyewiki.org/Implantable_Collamer_Lens
- Spectacle prescriptions normally treated as current for two years: College of Optometrists, "Prescriptions more than two years old" https://www.college-optometrists.org/clinical-guidance/guidance/knowledge,-skills-and-performance/sale-and-supply-of-spectacles/prescriptions-more-than-two-years-old
- Free NHS sight test every 2 years for eligible people: NHS, "How often can I have a free NHS eye test?" https://www.nhs.uk/nhs-services/opticians/how-often-can-i-have-a-free-nhs-eye-test/ (carried from the Online eye test page, where it was checked)
- Dioptre = reciprocal metre, 3 D focuses at one-third of a metre, 0.25 D steps; OU/RE/LE/plano/DS/ADD/PD definitions; transposition rule (flip cylinder sign, add 90° to axis, subtract 180° if over 180); back vertex distance (12–14 mm, significant beyond ±4.00 D): Wikipedia, "Dioptre" https://en.wikipedia.org/wiki/Dioptre · "Eyeglass prescription" https://en.wikipedia.org/wiki/Eyeglass_prescription · "Vertex distance" https://en.wikipedia.org/wiki/Vertex_distance (reference summaries; the reviewing surgeon may confirm against a textbook)
- Emergency numbers: 112 in the EU, European Commission https://digital-strategy.ec.europa.eu/en/policies/112 · 112 in Türkiye, 112.gov.tr https://www.112.gov.tr/kilis/acil-durumlarda-tek-numara-112 · 999 in the UK, NHS https://www.nhs.uk/nhs-services/urgent-and-emergency-care-services/when-to-call-999/ · 911 in Canada, Parks Canada https://parks.canada.ca/voyage-travel/securite-safety/urgence-emergency
- Own calculations (not external facts): spherical equivalent (sphere + cylinder ÷ 2), transposition examples, near power (sphere + ADD), the "mixed astigmatism" test (sphere and sphere + cylinder of opposite signs), the 61–120° / 1–30° / 151–180° orientation boundaries (to be confirmed by the reviewing surgeon), and the five QA samples.
Want to know what your prescription means for treatment?
Send us your prescription and one of our surgeons will tell you which treatments may suit you, with no obligation.
3 eye surgeons
Your case is reviewed by a named surgeon, not a salesperson. Reply within {{response time}}.
Prof. Dr. Ahmet Satıcı
Doç. Dr. Muhammet Derda Özer
Op. Dr. Aysan Bayram