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Explaining Your Prescription

Understanding Your Glasses Prescription

This guide is aimed at helping you understand and interpret your prescription so that you can enter the correct information into our online form to order your glasses. We encourage you to fax or email a copy of your prescription with your order and our staff are available during office hours to help with any questions you may have.

A typical prescription, issued by an optometrist, provides (almost*) all the information required for an optical technician to prepare lenses for your new glasses. The information provided in your prescription could be used to prepare

  • single vision distance glasses
  • single vision reading glasses
  • bifocal/varifocal glasses.

*Note the PD (pupillary distance measurement) has not been provided.

There is no accepted standard for writing prescriptions which can make it very confusing for an ordinary person to understand and interpret their prescription. Some of the most common things to look out for are:

  • Rx is shorthand for Prescription.
  • Distance Vision may be expressed as DIST, DV or Distance
  • Near Vision may be expressed as NEAR or NV.
  • Right Eye may be shown as R, RE or the Latin O.D.
  • Left Eye may be shown as L. LE or the Latin O.S.
  • A zero value in the SPH or CYL box may be writtin as 0, 0.00, Plano, PL or using the infinity sign which is like a numer 8 on its side ∞.
  • The negative sign for SPH or CYL values may be written before, above or below the number.

Type of Glasses

We can prepare all types of glasses for you. You need to tell us which type of glasses your require; distance glasses which you wear all the time, or reading glasses which you only wear while reading, working at the computer or focussing on things at arms length.
If you require distance glasses you only need to provide us with the row of information labelled DIST. If you require reading glasses you will need to provide the information in the both the DIST and NEAR rows.

Sphere (Sph)

This is the strength or power of lens required to correct your vision.

A plus (+) sphere is used to correct long sightedness (Hyperopia), where there is difficulty in focussing on close objects. The plus sign may be placed before, after or above the value, or there may be no plus sign.

A minus (-)sphere is used to correct short sightedness (Myopia) where there is difficulty in focussing on distant objects. The minus sign may written before, after or above the value.

Where there is no value this may be entered as 0 or Plano or PL or using the infinity sign, ∞

Cylinder (Cyl)

A cylinder value is used to correct astigmatism, this is where the eye, instead of being perfectly round has changed to more of a rugby ball shape.

Not everyone has a Cyl value on their prescription, or it might be only on one eye. If there is no value on your prescription then leave this field empty. This Cyl value may be in either plus or minus form. The plus or minus sign may be written before, after or above the value. If there is no plus or minus sign it is assumed that the value is plus. A Cyl value is always accompanied by an Axis value.


The axis value tells us how to align the cylinder correction in you prescription. You will only have an axis value if there is a cylinder value.

Enter a number between 1 and 180 (degrees) for the axis to which the cylinder is to be orientated.

Addition (Add or Reading Addition)

This power or value is the additional magnification required for preparing glasses for reading or computer work.

It may be included as a separate value on prescriptions for making bi-focal or varifocal lenses, which have both the distance and near correction powers. This value is only required if you select single vision reading lenses.

Pupil Distance (PD)

Your Pupil Distance (also know as Inter Pupillary Distance and PD) is the distance between the centres of your pupils usually measured in millimetres. It may be expressed as a single number e.g. 64mm or as a monocular PD, e.g. R32mm/L32mm where the measurement is given separately from the centre line for each eye. The normal range for the PD in the adult population is 54mm – 68mm

Prism & Base

These are absent from most prescriptions. A prism is used to treat muscular imbalance or other conditions that cause errors in eye orientation.

A prism will be used to displace the image seen by the eye through the lens. The base refers to the direction of the displacement. If you have a prism and base value on your prescription you will need to inform us about this separately and provide a copy of your prescription.