If you need vision correction following an eye exam, you’ll be given a prescription for corrective eyewear. Your prescription will contain a couple of abbreviated terms necessary for us to prepare your lenses, such as:
- OD (Right Eye)
- OS (Left Eye)
- SPH (Sphere)
- CYL (Cylinder)
- PD (Pupillary Distance)
Below you will find an explanation of what these abbreviations mean. This will hopefully be useful when interpreting your prescription.
OD is an abbreviation for "oculus dexter", Latin for "right eye" from the patient's point of view.
OS is an abbreviation for "oculus sinister", Latin for "left eye" from the patient's point of view.
SPH (always required)
SPH is an abbreviation of “sphere” which indicates the power of the lens your doctor is prescribing to correct your vision.
If you’re nearsighted (myopia), the number will have a minus sign (-). If you’re farsighted (hyperopia), the number will have a plus sign (+).
CYL (if applicable)
CYL is an abbreviation of “cylinder” which indicates the lens power your doctor is prescribing to correct your astigmatism. If this column is empty, then your doctor hasn’t found an astigmatism or your astigmatism does not need to be corrected. In that case, you should leave these fields blank.
Axis (only when a CYL number is indicated)
Axis is measured in degrees - ranging from 1 to 180 - and refers to where the astigmatism (CYL) is located on the cornea. If your doctor has indicated the need for cylinder power (CYL), there will also be an axis value to indicate the positioning for each eye. If your doctor has not found astigmatism, then there is obviously no need to fill in this information.
PD (always required)
PD stands for "pupillary distance" and represents the measurement, in millimetres, between pupil centres. For most people the distance from the centre of each pupil to the centre of the nose bridge is equal. Therefore, PD is often divided by 2. However, this doesn't have to always be the case, so make sure the values for both eyes are correct.
Final note: We do not offer bifocal lenses, thus it is not possible to insert "ADD" data when handing in your prescription to us.