You’ve had your eyes tested, what now?
You’ve been to your Optometrist, had your eyes checked and asked for a copy of your prescription. What now? And what do all those numbers mean? You can leave all that to the optical dispenser. However, if you are a curious person you may like a basic understanding of what you have been prescribed. So here is a short summary to make some sense of those numbers.
OD and OS: Latin terms for right eye and left eye
Sphere: Refers to the power of the lens, measured in diopters. If the number has a minus sign you are nearsighted; plus sign means you are farsighted. The further away from zero basically means the worse your eyesight. When no correction is needed, the prescription may state plano (pl) or 0.00.
Cyl: Cylinder lens power added to correct astigmatism which may be due to an irregular curvature of the cornea or lens. You may not have astigmatism so your prescription would therefore not include a Cyl power or Axis and you won’t need to enter it on the order form. If you do have it, then again the minus sign is for nearsightedness and plus sign for farsighted. A Cyl power must be followed by Axis.
Axis; If the prescription includes Cylinder power, it must also include an Axis value (X). This indicates the angle (in degrees) between the vertical and horizontal meridians of the astigmatic eye. The number is anywhere between 0 and 180 degrees.
Add: This is the plus (+) power that needs to be added to the distance lens prescription to give the patient clear vision at a close range for reading. Some prescriptions may include an intermediate Add designed for computer use and will be a lower number then the reading Add.
Prism: Only a small percentage of people need this on their prescription and it is to compensate for eye alignment problems. If you have prism on your prescription it is best to visit a local optical dispenser for a personal fitting.
PD: This is the distance (millimetres) between the centers of the pupils in each eye and is an important measurement for an optical dispenser to make prescription eyeglasses. It enables the correct positioning of the lenses and is particularly important in high powered lenses. Optometrists don’t always record it on your prescription so make sure you ask for it.
If you need any other advice or still aren’t sure, talk to our experienced Optical Dispenser/Mechanic.