Understanding your prescription
What do the numbers and words mean on your glasses prescription? Let us help you make sense of your prescription with our short guide.
You can also send us a copy of your prescription and we will read it for you.
Your prescription is what your optician recommends for clear and comfortable vision. All Opticians work to the same procedures when writing a prescription, which can be printed or written in a similar way to this sample prescription...
The Sphere (SPH)
The sphere is the strength of lens required to correct your vision. This is measured in Dioptre’s. Most values range from 0.00 to +/- 20.00 and go up in steps of 0.25.
- a plus (+) sphere is to correct long-sightedness (hyperopic - difficulty focusing on close objects)
- a minus (-) sphere is to correct short sightedness (myopia - difficulty focusing on distant objects)
- the word Plano or Pl or an infinity sign, means that you are neither long nor short sighted but zero power for the Sphere, however you may have astigmatism – a CYL and AXIS on your prescription.
The Cylinder (CYL)
If your prescription has a CYL and AXIS, this indicates you have an astigmatism.
What's an astigmatism? An astigmatism is where the eye is shaped slightly like a rugby ball or referred to as ‘toric’, not a perfect sphere like a football. This just means the eye has difficulty focusing at certain angles.
If you don’t have an astigmatism, this box will be empty. If you do have an astigmatism, this will be indicated by a plus (+) or minus (-) value. This is also measured in Dioptre’s and most values range from +/- 0.25 to +/- 4.00 and will go up in steps of 0.25.
The AXIS is only present if there is a value in the CYL box, the AXIS tells us where the astigmatism is on your eye. The measurement is in Degrees. The values range between 0 and 180 and may go up in steps of ½, 1, 5 or 10 degrees, we only show the AXIS to a whole number but if you have a ½ degree on your prescription you can list this in the additional information box when ordering.
The ADD (Addition)
The Add, short for Reading Addition, is the additional correction required for reading, this can be used to make either reading glasses, bifocal glasses or Varifocal glasses.
This number is an indication of how much extra power is required ‘on top’ of the distance prescription for near or intermediate glasses. Most values range from +0.50 to +3.50 and will go up in steps of 0.25.
The 'addition' is required if the glasses are going to be used for reading or close work. Sometimes opticians use the word 'Add' or 'Near' instead of 'addition'. Opticians may only write this value once, but it normally applies to both eyes and is almost always the same value for both eyes (e.g. 'Add' +2.50 should be entered for both eyes when you place your order).
Pupillary Distance (PD)
The Pupillary distance is an essential measurement. It is the distance from the centre of one pupil to the centre of the other pupil measured in mm (ranges from 50 to 70mm).
What is the pupillary distance measurement for? Each spectacle lens will have an ‘optical centre’, this is a point on the lens where it performs the best and has the least distortion. The optical centre of each lens should be placed directly in front of the centre of each of your pupils so your eyes are looking through the best point on each lens.
Some prescriptions may have the PD/Pupillary Distance listed for each eye respectively, for example RE: 32 LE: 32, you would enter 64mm from our list.
If the PD/Pupillary Distance for the glasses is not set correctly then your eyes may have to strain to look through them, this can lead to headaches, eyestrain, visual distortion and in severe cases, double vision.
The PD/Pupillary Distance is generally measured during a sight test, but is not routinely written on a prescription, you can ask for this from your Opticians, or ask them to add it to your prescription when you are tested.
For more help and information on PD measurement, see our guide here.
What is my glasses prescription for?
Distance / Intermediate / Near explained
Dist is distance, this is the prescription required to correct distance vision. This correction is often used for driving, television and general wear (walking around). These glasses are often worn full time.
Inter, is intermediate, this is the prescription required to correct intermediate vision, and may appear in full, or as an additional power (ADD) to the distance. If you require spectacles for intermediate use include the INTER ADD in the ADD box when ordering and also advise us in the additional info box that you require these for intermediate use. This correction is often used for computer (VDU) operation.
Near is the prescription to correct near vision and may appear in full, or as an additional power (ADD) to the distance. This correction is often used for reading, sewing and any detailed close work.
Back Vertex Distance (BVD)
The BVD stands for Back Vertex Distance, this is a measurement that is included on any prescription where the sphere or cylinder powers are higher than + or - 5.00D and to a lesser extent some prescriptions where it is less than this power.
This measurement is important as it explains at what distance your lenses should sit from your eyes. Usually your lenses will be positioned around 10-12mm from your eyes, however this will vary from person to person. If your prescription includes a BVD, it is important that the lenses sit at the correct distance to ensure comfortable vision.
If in doubt...
You can place your order by entering your prescription as it is written or you can email us a copy of it separately. For absolute peace of mind, you can do both! We will double check the prescription this end to ensure the correct lenses are produced.