Contact lens prescriptions use specialized abbreviations to ensure safe and accurate vision correction. These standardized notations allow eye care professionals to specify the precise lenses needed for each eye. Understanding this terminology is necessary to properly order lenses and maintain eye health, preventing discomfort or blurred vision that results from using the wrong lens in the wrong eye.
Deciphering the Key Terms: OD, OS, and OU
The abbreviation OD stands for the Latin term Oculus Dexter, which translates to Right Eye. This designation is always listed first on a prescription and refers to the unique specifications required for the right lens. Similarly, the term OS is an abbreviation for Oculus Sinister, meaning Left Eye. These Latin terms have been adopted universally in the optical field.
A third term, OU, stands for Oculus Uterque, meaning Both Eyes. If you see OU on a prescription, it indicates that the same measurement or correction applies equally to both your right and left eyes.
Reading Your Contact Lens Prescription
The abbreviations OD and OS form the structural basis of a contact lens prescription, organizing specific measurements for each eye into distinct columns or rows. The prescription lists several parameters beneath these headings, beginning with the Power or Sphere (PWR/SPH). This number represents the lens strength required to correct your nearsightedness (minus sign) or farsightedness (plus sign), measured in units called diopters.
Another significant measurement is the Base Curve (BC), which defines the curvature on the back surface of the contact lens. This value, measured in millimeters, is specific to the shape of your cornea and ensures a proper, comfortable fit. The Diameter (DIA) is also listed, indicating the overall size of the lens, measured edge-to-edge in millimeters.
If you have astigmatism, your prescription will also include Cylinder (CYL) and Axis values under the appropriate eye column. These specify the additional power and its orientation needed to correct the irregular curvature of the cornea. Because many people have different vision needs, the measurements under OD and OS are often not identical.
Practical Tips for Contact Lens Handling
To prevent accidentally swapping lenses, which can cause blurry vision or discomfort, establish a consistent handling routine. Eye care professionals often recommend always starting with the same eye, such as the right eye (OD), when inserting or removing lenses. This habit minimizes the chance of mixing up lenses, especially if your OD and OS prescriptions are different.
Contact lens cases are manufactured with “R” and “L” markings to maintain separation during storage. Always place the right lens in the well marked “R” and the left lens in the well marked “L.” If you accidentally swap the lenses and experience blurry vision, remove them, clean them properly, and reinsert them into the correct eyes. Following a methodical process ensures correct usage and protects eye health.