An eyeglass prescription often looks like a cryptic sequence of numbers and abbreviations. This technical language is a precise set of instructions for the lens manufacturer to correct specific vision needs. Understanding these terms provides insight into your eye health. This article clarifies common prescription abbreviations, focusing on how the spherical component (DS) and the cylindrical component (DC) determine the power of corrective lenses.
Decoding the Spherical Component (DS)
The term DS stands for Diopter Sphere, which addresses the most common types of refractive error. Spherical correction is needed when the eye causes light to focus in front of or behind the retina, resulting in blurry vision. The power of this correction is measured in Diopters (D), which indicate the lens’s optical power. The correction is called “spherical” because the required power is uniform across the entire lens surface.
This component corrects myopia (nearsightedness) and hyperopia (farsightedness). Myopia uses a negative sign (-) preceding the Diopter value, pushing the focal point backward onto the retina. A positive sign (+) indicates correction for hyperopia, adding power to pull the focal point forward. The entire spherical number dictates the overall lens power needed for clear focus. DS sometimes indicates the eye requires only spherical correction and has no measurable astigmatism.
Decoding the Cylindrical Component (DC) and Axis (AX)
The cylindrical component, abbreviated as DC (Diopter Cylinder) or sometimes CYL, addresses astigmatism. Astigmatism occurs when the cornea or lens is shaped more like the side of a football rather than a perfect sphere. This irregular curvature causes light to focus unevenly, resulting in distorted vision at any distance.
The DC value specifies the additional lens power needed to correct this difference in curvature along a single meridian of the eye. Since correction is required in only one specific direction, the lens power is not uniform, leading to the term “cylinder.” If this column is blank or contains “DS,” no cylindrical correction is necessary.
The DC value is meaningless without the Axis (AX). The Axis is a number between 1 and 180 degrees that identifies the precise angle where the cylindrical correction must be placed. The AX specifies the meridian that requires no cylindrical power. The DC determines the strength of the correction, while the AX determines its placement, ensuring perfect alignment with the eye’s curvature.
Interpreting the Full Prescription Format
The spherical (DS) and cylindrical (DC) values are organized into a standardized chart format using several abbreviations. The prescription separates data for each eye: OD (Oculus Dexter) for the right eye and OS (Oculus Sinister) for the left eye. OU (Oculus Uterque) may refer to both eyes when the values are identical.
The first numerical column usually lists the SPH or DS value, followed by the CYL or DC value, and finally the AXIS. The sign preceding these numbers is critical, as a negative sign (-) indicates correction for nearsightedness, while a positive sign (+) denotes farsightedness. The number itself represents the magnitude of the refractive error.
A final column is ADD, which stands for “addition.” This value represents the supplemental magnifying power required for reading or near vision, often for individuals over 40. This ADD power is combined with the distance correction to create bifocal, trifocal, or progressive lenses. The ADD power is nearly always positive and is typically the same for both eyes.