Eyeglass prescription

An eyeglass prescription or glasses prescription is a prescription for corrective glasses lenses. It specifies what strength of lenses the patient needs to see clearly. These prescriptions use dioptres as the measure. They usually have four sections.

The first one is the base power (also called sphere power) measured in diopters (dioptres). Prescriptions for hyperopia have a + sign in front of the number, while prescriptions for myopia have a - sign.

The second is the cylinder power, which is particularly for people with astigmatism. The cylinder refers to the type of corrective lens that treats astigmatism, called a cylindrical lens.

The third is the axis component, which measures the position of both the sphere and cylinder powers.

• See also: Corrective lens