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Definitions

1. Your prescription details are the results of your last eye test. They comprise the following values: sphere (Sph), cylinder (Cyl), axis (A) and addition power (ADD). On all prescriptions you will find a sphere value. If you have astigmatism, you will also find values for cyl and A. Multi-focal lenses for presbyopia have an addition power (ADD).
2. The term base curve refers to the curvature of the inside surface of the contact lens. Larger base curves provide a looser fit to your cornea. Smaller (or "steeper") base curves provide a tighter fit.
3. The diameter of a contact lens refers to the size of the lens, from one side to the other. Smaller eyes will need smaller lenses, and larger eyes need lenses with a larger diameter.
4. The colour of your lenses.
5. The sphere is the basic strength of your contact lenses, measured in dioptres (D). If a plus value is indicated, then you are far-sighted. A minus value indicates short-sightedness.
6. Where a corneal astigmatism is present, cylinder value refers to the strength required to correct said astigmatism. It is measured in dioptres and can be a negative (short-sighted) or positive (far-sighted) value.
7. The axis value states the direction of the corneal astigmatism (irregular curvature of the cornea). It is measured in degrees from 0 to 180.
8. An addition power is found on prescriptions for presbyopia. It refers to the additional strength required for near vision. It can be a a +/- diopritic value (distant R/L: -2.00D and Add. R/L: +2.00D), but also an ascending valule(distant R/L: +2.00D and Add. R/L: +2.00D - +4.00D).