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How to Read an Eyeglasses Prescription

  • Published: 2010-05-23 (Revised/Updated 2013-06-04) : Author:
  • Synopsis: Understanding your eye glasses prescription will enable you to custom order the right lenses.

Main Document

"Prisms are used in eyeglasses generally when people have a slight squint or lazy eye by changing the way light is directed."

Over time you might discover that you need a pair of prescription eyeglasses.

The first step is to always book an eye test with your local optician, which at its end you'll be given your prescription.

Understanding your prescription will enable you to custom order the right lenses (if bought online), to better understand your eye health and to compare changes over time.

To help you get to grips with your prescription, this guide will take you through the various parts.

Your prescription will generally look something like this:

Prescription sample for eye glasses
About This Image: Prescription sample for eye glasses

SPH: All prescriptions have SPH or SPHERE figure. This indicates the strength of your prescription in 0.25 increments. SPH beyond +/-8 is considered very strong prescription which will require extra special fitting by your optician.

CYL: If you have a common condition called Astigmatism, this figure is required. Also known as CYLINDER figure, it should be between +/-4 in 0.25 increments. In some cases opticians write 'DS' in the CYL column. This simply means there is no astigmatism.

AXIS: If your prescription has a CYL reading then it should have an AXIS reading between 0-180. It is important to note that not all prescriptions have CYL/AXIS values and and you may have it written down for one eye only.

ADD or NEAR ADDITION: The addition value is the amount to add to the SPH value for reading or intermediate glasses and sometimes for computer work. You might find this value outside of the ADD box in some cases. Opticians often write this figure all over the prescription, sometimes once (same for both eyes) sometimes once for each eye.

BALANCE (Optional): This note is written when there is little or no vision in one eye, and the optician wants to make sure that the lenses match weight and thickness for cosmetic reasons.

PRISMS (Optional): Prisms are used in eyeglasses generally when people have a slight squint or lazy eye by changing the way light is directed. The prism relieves strain by letting your eyes use a position that is more natural and comfortable.

PUPILLARY DISTANCE/PD (Optional): This figure measures the distance between your eyes so that the center of each lens is aligned with the center of the your pupils.

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