Base: The orientation of the prism in your lenses. If you are over 45, your prescription might also contain the letters ‘ADD’ after the numbers. This is your ‘reading addition’ – an extra correction to help you focus close up. 

Sphere (SPH): This indicates the amount of lens power, prescribed to correct near-sightedness or far-sightedness. The higher the number, the stronger the lens. For example, 0.25 would indicate a weaker lens, 6.00 a very strong one. If the number under this heading has a minus sign (–), you are near-sighted; if it has a plus sign (+), you are far-sighted. 

Cylinder (CYL): The extent of any astigmatism (irregularly shaped cornea) you may have – that’s to say, how spherical or oval your eyes are. This box will be empty if you have no astigmatism, which means your eyes are perfectly spherical. A low number (like 0.25) means that your eyes are rounder; a high number (say 3.00) means they are more oval. 

Axis: The direction of any astigmatism (in degrees). This doesn’t affect your sight, but does affect the positioning of the lens within your frames.

Prism: Whether or not you need prism lenses. These help correct any muscle imbalance between your eyes which can lead to double vision and headaches. Only a small percentage of prescriptions include prism.