An eye prescription slip often presents a confusing array of letters and numbers that seem like a specialized code. Understanding these abbreviations is the first step in knowing how your vision is being corrected and what your specific needs are. This documentation decodes the medical shorthand used on your prescription, translating it into clear terms so you can understand your vision correction requirements and the lens power needed for sharp, comfortable vision.
Deciphering OD, OS, and OU
The most prominent abbreviations on an eye prescription are OD, OS, and OU, which are Latin terms used to designate the eye being measured. OD stands for Oculus Dexter, which refers specifically to the right eye, and is typically the first line item on a prescription form. OS stands for Oculus Sinister, which designates the left eye, and is listed second.
The third abbreviation, OU, stands for Oculus Uterque, and translates to “both eyes.” This designation is used when the vision correction required is exactly the same for both the right and the left eye. While OD and OS are used to detail the specific measurements for each eye, OU indicates a symmetrical prescription.
Understanding the Numerical Measurements
The main corrective lens power is listed under the SPH, or Sphere, column, which measures the strength needed to correct farsightedness or nearsightedness. This value is measured in diopters, representing the degree of lens power required for clear vision. If this column contains a value of 0.00 or the term “Plano” (PL), it means no spherical correction is needed for distance vision in that eye.
The CYL, or Cylinder, value indicates the specific amount of additional lens power required to correct astigmatism. Astigmatism occurs when the cornea is shaped unevenly, causing light to focus improperly. The AXIS number, a degree between 1 and 180, specifies the exact orientation or angle where the cylindrical power must be placed on the lens.
The ADD, or Addition, value is a positive number representing the extra magnifying power required for reading and other close-up tasks. This value is included for those who need bifocal, trifocal, or progressive lenses, often due to the age-related condition known as presbyopia. The ADD value is usually the same for both eyes and is applied in addition to the distance prescription.
Connecting the Prescription to Vision
The sign preceding the SPH value directly translates the type of vision problem being corrected. A negative sign (-) in the Sphere column signifies myopia, commonly known as nearsightedness, which means objects far away appear blurry. This negative power indicates a diverging lens is needed to push the focal point backward onto the retina.
Conversely, a positive sign (+) in the SPH column indicates hyperopia, or farsightedness, where distant objects are seen clearly but close-up items are blurry. This positive power specifies a converging lens, which helps pull the focal point forward onto the retina. The presence of both a CYL and an AXIS value confirms the existence of astigmatism.