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Eyeglasses Prescription Explained

Eyeglass prescriptions are completely confusing to the general public.  Here are a few simple tips to help you understand your glasses prescription so that you can order new glasses online with confidence.

Prescriptions are made up of numbers and symbols.  An example of a prescription is:

Right               + 2.00 / -0.50 x 180

Left                 - 1.25 / -0.75 x 180

                       Sphere/ Cylinder x Axis

                       Add     +1.50               PD 62mm

This prescription will be broken into parts to make it easier to understand.

Sphere (Sph):  This part of the eyeglass prescription generally corrects for either long sightedness or short sightedness using plus or minus lenses respectively.  Therefore the above prescription could be said to be correcting long sightedness in the Right eye and short sightedness in the Left eye. The higher the number wrote for the Spherical component the more significant the vision problem. (More information is available on long and short sighted vision problems in an article available at Only Specs).

Cylinder (Cyl):  Is commonly given a minus value, though some Ophthalmologist and old school Optometrists' still write their prescriptions in plus form.  If you have a number written in this section of your prescription then it is likely that you have Astigmatism.  The higher the value the more Astigmatism that is present.  Astigmatism implies that the curvature of the cornea or the lens within the eye is not spherical.  This can create blur around the edges of objects that gets worse in the evenings. If your prescription has a value greater than -2.00 written then it is probable that you will need to have special lenses made which incur an increased cost.

Axis: Is the angle that the prescription lens will be placed in the frame to correct the Astigmatism.  It has a value from 1- 180 degrees.  Commonly the axis is either 90 or 180 degrees. 

Add: A value written in this section of your prescription can indicate the need for separate close work glasses.  An example would be computer or reading glasses.  The eyeglass prescription written above has +1.50 to be added on to the distance prescription to give the reading prescription.  The reading prescription would be:

            Right               +3.50 / -0.50 x 180

            Left                 +0.25 / -0.75 x 180

Pupil Distance (PD):  Is the distance between pupil centres in millimetres.  Important for fitting the optical centres of the lenses in front of the customers pupils.

Only Specs Optometrists hope that you feel confident purchasing prescription glasses online.  Reading glasses from $49, order a pair today. www.onlyspecs.com.au

This article was published on Sunday 05 October, 2008.
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