SPH stands for Sphere and is an abbreviation used in eyeglass prescriptions to describe the amount of lens measured in diopters needed for good vision. The term means that the correction for your sight is spherical. If you are nearsighted, the number under the abbreviation will include a (-) sign, and if you are farsighted, the number will have a (+) sign. If your prescription has the word Plano, PI, or an infinity sign, it means that you do not have distance problems, but you may have astigmatism.