The Official GSC Guide to Reading Your Prescription
We won’t stop preaching about the importance of eye health to your overall well-being. Beyond the basic premise of, you know, just being able to see well, good eye health also contributes to your ability to exercise, work, and be your best self.
A good pair of spectacles can also provide you with all-crucial anti-blue light protection which protects frequent screen users (yes, we see you scrolling!) and helps them sleep better, or UV protection for sun lovers who love a forever tan but don’t love forever pupil damage.
We know, however, that searching for that perfect new pair can be all kinds of stressful, both on you and your wallet, especially when it comes to getting your measurements right.
First, your prescription:
Reading your prescription can feel intimidating, with many numbers and short-names - but we promise it’s very straightforward. Knowing your prescription is always helpful (it’s like knowing your waist measurements for buying new jeans) - because it means you’re proactively keeping track of your eye health.
Your eye prescription will tell you if you are:
- Near-sighted;
- Far-sighted; or
- Have astigmatism
And if your prescription is for single vision or progressive lenses.
You can determine this by the medical shorthand used within your prescription. Your prescription will usually come in a table like this, prescribed by an optometrist:
It’s helpful to note that most prescriptions are valid for 2 years, but some may only be for 1 or shorter if your optometrist believes you need to be seen more regularly. It’s important to keep on top of your appointments; just like a doctor check-up, they ensure your eye health stays on track.
O.D., O.S., and O.U. or O.D.S.:
These abbreviations stand for which eye the prescription belongs to. They are abbreviations for Latin terms for your eyes.
- O.D.: Oculus dexter, or your right eye;
- O.S.: Oculus sinister, or your left eye;
- O.U. or O.D.S.: Oculus uterque/ oculus dexter sinister, or both eyes
Sphere (or S.P.H.):
SPH is the amount of lens power you need to see correctly. It measures how near or how far-sighted you are. It is followed by a number which is used to measure the correction needed. The further that number is from 0, the stronger your need is.
If the SPH starts with a minus (-), it means you are near-sighted, otherwise also referred to as myopia. That means that you can clearly see close objects, but far objects may be challenging. The more near-sighted you are, the smaller the number will be. For example, -2 requires less correction than -5.
If the SPH conversely starts with a plus (+), it means you are far-sighted, otherwise referred to as hyperopia. You will find it easier to see faraway objects than close objects. The more far-sighted you are, the larger the number will be. For example, +2 requires less correction than +5.
Cylinder (C.Y.L. or C.) and Axis:
Astigmatism is known as a condition where your eyeball is not completely round. When the eye is completely round, light bends evenly around your eye, forming a clear picture. When your eye isn’t completely round, the light may not bend perfectly, meaning your vision may have some distortions.
If you do have astigmatism, your prescription will include a figure showing how distorted your eyeball is. The number can be positive or negative. The higher the number, the stronger the astigmatism.
Like SPH, if you don’t have astigmatism, or the effect is too minor to require correction, your number here will be 0.
If you have a C.Y.L. number, your Axis will explain where the irregular curve is affecting your vision. It should be a positive number, between 0 to 180 degrees, acting like a map of your eye.
These two figures work together to give a comprehensive understanding of your astigmatism and the requirements for correction. If you don’t have astigmatism in one or both eyes, your prescription should only include S.P.H.. If you have astigmatism, your prescription will include S.P.H., C.Y.L., and Axis numbers.
A.D.D., Prism and Pupillary Distance (P.D.):
“A.D.D.” equals “Added Lens Power” and makes it easier for you to read. This is common on prescriptions for reading glasses OR for the bottom part of your progressive or varifocal lens. These are most commonly used to correct age related long-sightedness, otherwise known as presbyopia, and are usually the same for both eyes. Usually this figure is between +0.75 and +3.00 D.
Prism is the amount of prismatic power if you have eye alignment problems. This is measured in prism dioptres (p.d. or a triangle). It also explains where to position the prism on the glasses using B.U. = base up, B.D. = base down, or B.I. = base in (i.e. towards the nose).
Finally, P.D., or Pupillary Distance, explains where the optical centre of your lenses should be based on the distance between your two pupils (or the black of your eyes). A P.D. number is incredibly important to ensure your prescription fits your spectacle frames, especially for progressive lens users.
Ocular Height (or O.C.):
Finally, you may also be asked for your Ocular Height, or O.C. calculation, which is otherwise known as your Ocular Centre. Progressive lens we arers and those with more complex prescriptions may be asked to provide this as additional information. Your O.C., along with your Pupillary Distance (P.D.), provide the vertical and horizontal alignment of your eyes to help you see perfectly.
Your optometrist should hopefully provide both measurements to you at the time of prescription, but if not - don’t worry! The PD+ app (iOS) does all the optical math for you and takes no more than a few minutes from your phone.
Other important stuff!
Your prescription may also include and describe other features which are important, such as the requirement of an anti-blue light lens (for those who work a lot in front of screens, or spend too much time on IG, scratch resistant coatings, or polarised lenses for those who spend lots of time in the sunshine.
If you have any other questions, feel free to reach out to the Greenwich Social Club Customer Happiness team. We’d be happy to help!