The short answerA glasses prescription gives three main numbers for each eye. SPH is the power for short-sightedness (minus) or long-sightedness (plus). CYL is the power for astigmatism. AXIS is the direction of the astigmatism from 1 to 180 degrees, not a strength. You may also see ADD for reading glasses after 40, and PD, the distance between your pupils. Powers change in steps of 0.25.
Right, left, distance and near
- OD, RE or R: right eye.
- OS, LE or L: left eye.
- OU: both eyes.
- DV or Distance: distance glasses. NV or Near: reading glasses.
SPH: short-sighted or long-sighted
A minus number (such as -2.00) means short-sightedness: near things look clearer than far things. A plus number (such as +1.50) means long-sightedness: the eye works harder, especially when reading. The further from zero, the stronger the lens. PL or Plano means zero.
CYL and AXIS: astigmatism
Astigmatism means the cornea or lens is not curved evenly in every direction, so images look stretched or have doubled edges. CYL is the power of the correction and AXIS is the direction it is placed in. No axis is better than another: 180 is not stronger than 90.
Example: "-2.00 / -0.75 × 180" means 2 dioptres of short-sightedness with 0.75 of astigmatism at axis 180. Some practitioners write the same lens with plus cylinder, which looks different on paper but is the same lens, so do not compare prescriptions from two places number by number.
ADD and PD
- ADD: extra power for reading, usually from about 40 onwards with presbyopia. It is added on top of the distance prescription.
- PD: the distance between your pupils in millimetres, which the optician uses to centre the lenses.
Glasses and contact lens prescriptions differ
A contact lens sits on the eye, while glasses sit about 12 mm in front of it, so above roughly 4.00 the required power changes. Contact lenses also need a measurement of the cornea's curvature.
When is a changing prescription a warning sign?
A small change in short-sightedness is normal in children and teenagers. But astigmatism that rises every year, an axis that keeps shifting, or new glasses that no longer reach 6/6, especially with itchy eyes and eye rubbing, call for a corneal scan (topography) to rule out keratoconus. Finding it early allows it to be stabilised before vision drops.
Frequently asked questions
Do I need glasses for -0.25?
Usually not, unless you get eye strain or headaches when reading or driving. The decision depends on your symptoms, not the number alone.
Can I work out my 6/x vision from my prescription?
Not accurately. The prescription measures the lens power you need, while 6/6 measures what you actually read. Two people with the same prescription can see differently without glasses.
My prescription is high. Can I have LASIK?
It depends more on the thickness and shape of your cornea and how stable your prescription is than on the number itself. For people who are not suitable for LASIK there are alternatives such as ICL lenses. You can start with the LASIK candidacy test and then an exam.