An eyeglass prescription is a set of lens specifications, not a single score of how well you see. The labels identify which eye each value applies to and what kind of optical correction it describes.
Start with the eye labels and sphere value
Look for the right-eye and left-eye labels before interpreting any numbers. OD means the right eye, and OS means the left eye. A prescription may place these columns in either order, so rely on the printed labels rather than assuming the first column always represents the same eye. Some forms use “Right” and “Left” instead.
SPH, short for sphere, describes the main focusing correction in the lens. Its value is measured in diopters. A minus sign indicates correction for nearsightedness, while a plus sign indicates correction for farsightedness. The sign tells you the direction of the prescribed optical correction; the size of the number describes lens power.
For example, a sphere of -2.00 and one of -6.00 both indicate nearsightedness correction, but the larger magnitude represents a different lens power.
Decode cylinder, axis, and near-add values
CYL, or cylinder, specifies the amount of astigmatism correction. Astigmatism involves a difference in focusing across directions, and the cylinder value gives the lens power used for that correction. CYL may be shown with a plus or minus sign, depending on how the prescription is written. A blank CYL field may reflect the form’s layout rather than a missing value.
When a cylinder value is present, an AXIS value often appears beside it. Axis indicates the orientation of the cylinder correction, using a number from 1 to 180 degrees. It is not another measure of how strong the correction is. A value such as 180 identifies an orientation; it should be read together with CYL rather than interpreted on its own as a severity score.
ADD means additional lens power for near vision. It is commonly included in multifocal prescriptions, where lenses are designed to support more than one viewing distance. ADD is separate from the distance sphere value, so it should not be added to SPH casually or treated as a second sphere measurement for every purpose. Read it as a distinct, labeled part of the lens specification.
Recognize prism and the limits of the document
Some prescriptions include prism, a separate lens specification that redirects light. A prism entry may be accompanied by a base direction, which describes its orientation. These details are not interchangeable with sphere or cylinder: they answer a different optical question.
Even a prescription with many completed fields is not a full report on the health of the eyes. Its values describe correction specified for glasses; by themselves, they do not identify why a vision problem developed, establish the condition of the eye, or provide a complete account of visual ability. That distinction matters when comparing prescriptions over time: a changed lens value records a change in the prescribed correction, but the document alone does not explain its cause.
Work through a sample without treating it as your prescription
Consider this hypothetical right-eye line: SPH -2.00, CYL -0.75, AXIS 180. The OD or “Right” label identifies the eye. The minus sphere indicates nearsightedness correction; the cylinder value specifies astigmatism correction; and 180 gives the cylinder’s orientation. Each entry has a different job, so reading the line means interpreting the labels and values together, not treating all three numbers as variations of the same measurement.
This example is only a demonstration of notation, not a suggested prescription or a basis for choosing glasses. When checking your own document, first match each number to its printed field, then distinguish an absent field from a value that is hard to read. If an abbreviation, sign, or entry remains unclear, the professional who issued the prescription can explain that specific notation. For neutral local directory navigation, view Newport Vision Center.