Looking for a new pair of eyewear but you’re not able to decipher those symbols, numbers and abbreviations on your prescription card? We’ve got you. If you wear glasses or lenses, then you’re familiar with the odd series of letters and numbers that make up your prescription card. But what do all these numbers, abbreviation and symbols mean? Read on, let’s help you make sense of your eyewear prescriptions.
Your Prescription: After an eye exam, you’ll receive an eyewear prescription card with specific information about your eyesight and correction needs. When writing a prescription, opticians work with the same procedures which can be printed or written similarly. Therefore, your prescription card will most likely have the following symbols and abbreviations:
OS and OD
Your eyewear prescription has numbers listed under the headings of OS and OD. These words are the Latin abbreviations: OS (oculus sinister) which means the left eye and OD (oculus dexter) which means the right eye. Occasionally, you might see a notation for OU (Oculus Uterque) meaning both eyes.
The sphere is the strength of the lens required to correct your vision. It is measured in Dioptres (D). Its values range from 0.00 to +/- 20.00 and go up in steps of 0.25. If the number appearing under this heading has a minus sign (–), you are short-sighted; if the number has a plus sign (+) or is not preceded by a plus sign or a minus sign, you are longsighted. Also, other symbols that can be found in this section are the infinity symbol (which looks like a sideways eight) or the word Plano (Pl). This is equivalent of ‘zero’ and is used when no sight correction is required. Another common term that can be found on prescriptions is V/A (or visual acuity) which measures the standard of vision when corrected.
This shows the severity of any astigmatism you have, and the number can be negative or positive. Astigmatism is when the front part of your eye is shaped more like a rugby ball than a regular circle. However, making it difficult for the eyes to focus at certain angles. If you, however, don’t have astigmatism, there will be no figures written in the cylinder and axis boxes. Although you may see DS written in the column, it stands for dioptre sphere and means you have no astigmatism. The number in the cylinder column may be preceded with a minus (-) sign (for the correction of short-sighted astigmatism) or a plus (+) sign (for longsighted astigmatism). Cylinder power always follows sphere power in a spectacle prescription.
The AXIS is measured in degrees, and the values range between 0 and 180. Therefore, the axis is the lens meridian that is 90 degrees away from the meridian that contains the cylinder power. It is only present if there is a value in the cylinder box. Therefore, if a spectacle prescription includes cylinder power, it also must include an axis value, which follows the cylinder power and is preceded by an “x” when written freehand. The AXIS tells your doctor where the astigmatism is on your eye.
Near add and intermediate add
Near add and intermediate add also written as Add is the additional correction you may need to focus at short distances. However, it is the added magnifying power applied to the bottom part of multifocal lenses to correct presbyopia. It is more common over the age of 40. The intermediate add refers to the additional strength of lenses you may need to bring a ‘mid-range’ distance in focus (usually the distance to a computer screen you are viewing), and the near add is usually for close tasks such as reading. Not all prescriptions will have a section for the intermediate add.
Pupillary Distance (PD)
The Pupillary distance is the distance from the centre of one pupil to the centre of the other pupil measured in mm (ranges from 50 to 70mm). Some prescriptions usually have the PD/Pupillary Distance listed for each eye, respectively, for example, RE: 32 LE: 32. Generally, the optician will not add this to your prescription, so you should ask for it; as those with high-strength prescriptions need to have lenses that are centred more accurately. 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.
Prism is the short word for prismatic power. It is a special type of correction built into the lens when eye alignment needs assistance. However, this is when both your eyes may have some difficulty working together. Prism is measured in prism diopters (“p.d.” or a superscript triangle when written freehand). The number in the prism column shows the strength of the correction, and the base column shows which direction the prism is acting in.
BVD (Back Vertex Distance) is the distance in millimetres between the front of your eye and the lens of your glasses. This measurement 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 distance can inﬂuence the eﬀective strength of a lens and is usually only given for higher-strength prescriptions. Gone through all this and still not sure about anything on your eyewear prescription? Your optometrist or dispensing optician can help.
How to read your glasses prescription