A soft lens prescription is fairly straightforward.
In the examples above the words identify the lens brand. The first number (8.60 in each case here) states the back central optic radius or BCOR in millimetres. Put simply, the contact lens fitter matches this to the shape of the cornea. The second number (14.10 or 14.30 in these examples) tells us the overall diameter of the lens in millimetres. Generally, toric lenses are slightly larger lenses to help them stabilise on the eye. In the case of the toric example the remaining numbers tells us the additional power on the lens that corrects astigmatism and the orientation of that extra power. Finally, the multifocal lens has words or numbers that indicate the highest reading power available on the lens – in this case a Low Add gives up to 2.25dioptres of extra reading power.
A hard or rigid lens prescription may be similar but with more detail, for example:
OE90 is a code for the design and material of the lens. Often the number indicates the degree of gas permeability and the higher the number the more oxygen permeable the lens material. Traditionally, the back of a rigid lens is not one single curve but a series of three or more curves. The pairs of numbers above (7.90:9.80 and 8.70:8.60 and 10.75:9.20) tell us the radius of that curve followed by the largest diameter of the same curve in millimetres. 9.20mm, therefore, is the overall diameter of the lens. The power of the lens is -3.25 dioptres and this lens is to be coloured blue.
Computer aided designs now mean that rigid lenses are usually aspheric so a prescription might simply be given as Manufacturer/Brand Name/Overall Diameter/Power.Back