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Understanding your Prescription

After your eye test you will receive a copy of your prescription for your records. Here’s a short guide to help your understand the numbers. Remember, if you have any questions about your prescription we are here to answer your queries.
Prescription image*Image: Association of Optometrists
SPH: Spherical error. This shows whether you are short-sighted (minus) or long-sighted (positive). The number represents the strength of lens your optometrist has found you need. If you have the letters ‘PL’ in this section, this is short for plano and mean there is no refractive error in this eye.
CYL and axis: If you have astigmatism, which is very common, this part of your prescription will be filled in. CYL is short for cylinder and shows the severity of astigmatism. The axis shows the degree at which the lens must be set to correct your astigmatism. If this box has the letters ‘D.S.’ (dioptre sphere) you have no astigmatism.
Prism and base: If your eyes are having difficulty working together, prism can help correct your binocular vision. The number represents the strength of the prism and the base shows which direction the prism is working in.
Near add: This number represents the power added to the spherical error in your lenses to help you focus at a near distance. This is common around the age of 40 and is the reason you’ll rarely find somebody over this age without reading glasses.
Intermediate add: Similar to the reading add, this number is added to your spherical error to help with intermediate distances. This is usually used if you spend a lot of time on a computer, which sits further away than a normal reading distance.
BVD: This stands for back vertex distance. People with a higher lens strength will often have this number on their prescription. This is because the distance between the eye and the lens of the glasses can have an influence on the effect of the lenses at these strengths, so must be brought into consideration.

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