How To Read Your Prescription.
Entering the right prescription is an integral part of purchasing eyeglasses online. Especially if you want to avoid bumping into things! Ouch!
Every written prescription contains similar information; no matter if it’s written by an Optometrist, Ophthalmologist or your shady Uncle Henry. Your prescription should contain information for both eyes represented as OD (right eye) and OS (left eye).1. Additionally, the prescription should include Sphere, Cylinder, Axis, ADD, and PD. Make sure you are paying close attention to the + and – signs on your prescription as described below.
The sphere portion of your prescription tells us if you are either nearsighted or farsighted. In most cases a negative number would represent someone who is nearsighted and those who have a positive number would usually be farsighted. Those who are nearsighted can see objects that are close by but have blurred vision when it comes to objects that are further away. Those who are farsighted can clearly see objects at a distance, but have difficulty seeing objects that are closer in distance. If your vision is faulty in only one of your eyes, a horizontal 8 is written on your prescription which indicates a 0.00 prescription in one eye which is also referred to as a “plano” lens.
Cylinder or CYL
The cylinder portion of a prescription indicates the presence or absence of astigmatism. The cylinder number indicates the difference in curvature and power between two points on the eye separated by 90 degrees. No cylinder number? No astigmatism! Yippee!
If you have astigmatism then you should always have a number in your axis section on your prescription. Your axis number is a whole number measured in degrees and should always be between 1- 180. The axis in a prescription describes orientation of the axis of the cylindrical lens. The direction of the axis is measured counter-clockwise from the horizontal line through the centers of the pupils when viewed from front side of the glasses.
ADD or Near Addition
ADD in the eyeglass world is not the same as the ADD of hyperactive children. ADD generally indicates a bifocal lens, i.e. problems with vision near and far.
PD which is short for pupillary distance is something that not every doctor supplies their patients with. You can always ask your doctor to write down this measurement for you if they do not supply you with one. Your pupillary distance is the measurement between the middle of your left pupil to the middle of your right pupil. If you do not have a measurement for you PD you can always have someone measure it for you. All you need is a ruler and someone to take the measurement for you. Make sure when you are measuring the distance between the two pupils that you are measuring it in millimeters. The correct pupillary distance measurement is important because it helps you have a more comfortable and optimal optic fit. The average PD is approximately 63mm; most people fit in the range of 54mm to 74mm.