The shape of your cornea is unique, as a result there are a number of factors that will influence the type of contact lenses that will be specific to you. Usually there are between 3-7 elements which make up a contact lens specification.
Most prescriptions will only contain 3 of these elements, however in some prescriptions additional elements are required depending on the type of lenses.
This is the power that is required to correct long and short sighted prescriptions. This may be positive (+), negative (-) or perhaps zero (Plano).
This element represents the curvature of the lenses, which ultimately corresponds to the curvature of your eyes. This may be different for each eye, however this value must be listed on your prescription for it to be valid.
The diameter represents to size of the lenses. This may be different for each eye, however this value must be listed on your prescription for it to be valid.
Other elements that may be present on your contact lens specification would include all of the above plus one or more of the following elements, depending on the type of lenses required.
This element indicates if your eye is irregular in shape and as a result astigmatic. When a Cylinder is present this will be accompanied with an axis value too.
This element indicates the orientation of the cylinder. This number is no indication of the power of the cylinder, only the direction of the cylinder power.
This element specifies any additional correction on top of your normal prescription required to enable close up vision.
This element indicates which eye is dominant, as one eye may be used for farsightedness and the other for nearsightedness.