In an eye prescription, the term "sphere" (SPH) refers to the amount of lens power, measured in diopters (D), prescribed to correct nearsightedness or farsightedness. If the number appearing under this heading has a minus sign (–), it indicates nearsightedness, while a plus sign (+) or no sign indicates farsightedness. The sphere correction is spherical, equal in all meridians of the eye, meaning that it is the same in all directions. The sphere value is usually measured in increments of 0.25 diopters.