What Does Sphere, Cylinder and Axis Mean?
If you’ve ever looked closely at your eye glass prescription, you’ve probably wondered what the numbers and terms mean. In order to be interpreted worldwide, eyeglass prescriptions are written in a standardized format with common notations. Notable terms include:
Sphere (SPH) – The term “sphere” means that the correction for nearsightedness or farsightedness is spherical, equal in all meridians of the eye. This indicates 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 (–), you are nearsighted; if the number has a plus sign (+) or is not preceded by a plus sign or a minus sign, you are farsighted.
Cylinder (CYL) – This indicates the amount of lens power for astigmatism and represents the difference in the greatest and weakest powers of the eye, usually separated by 90 degrees. If nothing appears in this column, either you have no astigmatism, or your astigmatism is so slight that it is not necessary to correct it with your eyeglass lenses. The number in the cylinder column may be preceded with a minus sign (for the correction of nearsighted astigmatism) or a plus sign (for farsighted astigmatism). Cylinder power always follows sphere power in an eyeglass prescription.
Axis – If an eyeglass prescription includes cylinder power, it also must include an axis value, which follows the CYL power. The axis indicates the angle (in degrees) between the two meridians of an astigmatic eye. The axis is defined with a number from 1 to 180. The number 90 corresponds to the vertical meridian of the eye, and the number 180 corresponds to the horizontal meridian.
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