At the end of your eye test you will be given a Prescription

which will look something like the example below. A prescription is usually valid for two years, but your optometrist may recommend that you have your eyes tested more frequently than this, depending on your particular circumstances. 

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SPH (Sphere)
This represents the amount of long and short sight that is present. Plus lenses are used to correct long sight and minus lenses are used to correct short sight.

CYL (Cylinder)
This represents the amount of astigmatism that is present. Astigmatism is caused when the eye is not completely spherical. This causes the vision to be distorted for both distant and near objects.

AXIS
This represents the orientation of the cylinder (from 0-180 degrees) and is the angle at which the lens is set into the frame.

PRISM
This is the correction needed (if any) to align the eyes, so that they are looking straight and working well together. A prism is a lens that bends the path of light without altering its focus.

ADD
This is the amount of correction that must be added to your prescription.
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