Refractive

The numbers that your Optometrist writes on your glasses prescription describes your refractive error. The numbers are measured in dioptres (D). The sphere column indicates how shortsighted or longsighted you are. If the number has a plus (+) symbol, this indicates that you are longsighted and that you need a convex lens to correct your vision. If the number has a minus (-) symbol, this indicates that you are shortsighted and that you need a concave lens to correct your vision. If you have astigmatism, then there will be a number in the cylinder section which might have a plus (+) symbol or a minus (-) symbol. The axis column describes the orientation of your astigmatism (the position of the axis of the rugby ball) in degrees from the horizontal.

Astigmatism is corrected with cylindrical lenses. Cylindrical lenses are usually part of a prescription for short or longsightedness. If you require reading glasses, there will be an additional number known as the 'add'. This always has a plus (+) symbol and has to be added to your distance prescription to calculate the strength of your reading glasses or bifocals.

This means that the right eye has 2.25D of shortsightedness with 1.75D of astigmatism (the axis being 180°) and the left eye has 1D of shortsightedness with 1D of astigmatism (the axis being 180°). This patient will need 2D extra power in the lenses for reading (the 'add').