Your prescription explained

Creating a new pair of glasses is a precise art that requires an exact set of measurements of the wearer. A precisely written prescription allows opticians to create lenses that effectively correct the wearer’s vision. In order to experience an enhanced quality of life through corrective vision, it is important for an optician to have the most accurate numbers and values available.

Understanding an the prescription can be a bit of a challenge, especially if one is not familiar with the terms used. However, once one is acquainted with the meanings behind these terms, it becomes relatively straightforward to understand and can give you an idea of exactly what your glasses will be correcting.

This guide provides a basic overview and explanation of the numbers and values that are used in the average spectacle prescription. Some of the terminology used may differ slightly, but most prescriptions are written based on certain terms and abbreviations.

Standard Eyeglass Prescription Terms

The average prescription gives sight evaluation values for the right and left eye. These values include:

  • SPHERE (SPH) – The corrective value for long sightedness is denoted with a plus or [+] symbol and for short sightedness is denoted with a minus or [-] symbol.
  • CYLINDER (CYL) – This term is used to denote a corrective value for astigmatism, if present.
  • AXIS – The axis is used to denote the angle for the correction of the CYL.
  • ADDITION (ADD) – This value is used to denote the amount of power added to a prescription if one requires eyeglasses for seeing objects up close or for reading. This value is always denoted with a [+] or plus sign.
  • PRISM and BASE – These values are put in use to correct double vision, although their use is relatively uncommon.

The plus and minus symbols are always included on prescriptions to measure the corrective need for one’s sight. These symbols are essential for denoting whether the eyeglasses prescription calls for a correction of long or short sightedness. For example, the SPHERE (SPH) and CYLINDER (CYL) values will always consist of a plus or minus power (SPH -1.25 CYL -0.50).

The AXIS value is only used in the case of astigmatism and is only present whenever there is a CYLINDER (CYL) value. The AXIS value usually ranges from 0 to 180.

The ADDITION value is used for those who require glasses for reading and for those who need bifocals or varifocals. This value will always consist of a power with a plus symbol (ADD +2.00).

In many cases, those in need of bifocals or varifocals will have a distance and reading prescription. For example, the distance prescription may be “R SPH -4.50 and L SPH -3.00,” while the reading prescription is “R SPH -2.50 and L SPH -1.00.”

Glossary of Abbreviations and Terms

  • 0.00, infinity (∞), Plano, Pl – These terms are used to denote that no sight correction is necessary.
  • Right, R or OD – Denotes the right eye.
  • Left, L or OS – Denotes the left eye.
  • DV – Distance vision.
  • NV – Near vision.
  • PD – This abbreviation is used to denote the distance between the centres of your pupils, also known as PUPILLARY DISTANCE; it is expressed in millimetres.

PUPILLARY DISTANCE or PD is considered particularly important if one has a particularly strong eyeglass prescription. This value is usually not measured during the eye examination. Instead, this measurement is usually taken by the dispensing optician while purchasing the new eyeglasses. Unlike the other optical values, opticians are under no obligation to supply the PD value. In many cases, there is an additional charge for having this measurement taken.

It is important to have confidence in your prescription and it is always recommended that you have your glasses made with the opticians that prescribed it. Please contact us if you would like to have an eye test or book online now.