How to read your eyeglass prescription

An eyeglass prescription is for the purchase of eyeglasses only. It does not contain certain information that is crucial to a contact lens prescription and that can be obtained only during a contact lens consultation and fitting.

Your eyeglass prescription contains information regarding the lens power required to correct your vision problems. It consists of spherical power, cylindrical power, cylinder axis, bifocal addition, and prism power. Your prescription will contain only those numbers that are pertinent for your vision correction, for example if you do not have astigmatism, you would not have a cylindrical power and axis information in your prescription. Most prescriptions do not contain prism power.

To be able read and understand your prescription you should understand the abbreviations used by ophthalmologist:

What does OD and OS stands for:

The two most important of these mystery terms and abbreviations are OD and OS. These are Latin terms that mean OD – (Oculus Dextrus) right eye and OS – (Oculus Sinister) left eye.

What is sphere power?

This is the main part of your prescription. This number denotes the strength of the lens as measured in diopters.

What is a diopter?

A diopter is a unit of measurement that is simply the inverse of the focal distance of the lens as measured in meters. For example, if a lens has strength of 2 diopters, then parallel light rays that pass through this lens will focus together at a distance of 1/2 meter (50 cm) away from the lens.

What is cylindrical power?

If there is no value under the cylinder heading, then you have a simple prescription. If there is a value under this heading, then you have astigmatism. Like sphere power, the cylinder power is also measured in diopters

What is an axis?

This describes the lens meridian that contains no cylinder power to correct astigmatism. The axis is defined with a number from 1 to 180. The number 90 corresponds to the vertical meridian of the eye, and the number 180 corresponds to the horizontal meridian.

What is ADD?

This is the added magnifying power applied to the bottom part of multifocal lenses to correct presbyopia. The number appearing in this section of the prescription is always a “plus” power, even if it is not preceded by a plus sign. Generally it will range from +0.75 to +3.00 D and will be the same power for both eyes

What is PD?

The PD or Pupillary Distance is the distance between your two eyes , center to center, the center of one pupil to the center of the other, in Millimeters.

Some prescriptions have two numbers, written such as PD 65/62 usually written on a bi-focal prescription. This means that 65 is your distance vision PD, and the one to be entered on our forms. And 62 is the reading or near vision PD, the one to be used only if you are ordering a plain reading glass only.

The optician will measure the precise inter-pupillary distance (PD) to ensure accurate placement of lenses in the frame.