Eye prescriptions use standardized abbreviations recognized globally by eye care professionals. These terms ensure clear communication regarding specific vision needs. Understanding the abbreviations that designate the eyes is the first step toward knowing exactly what your prescription means for sight correction.
Decoding the Terminology: OS, OD, and OU
The abbreviation OS stands for Oculus Sinister, which is Latin for “left eye.” This term designates all measurements specific to the lens required for the left eye. Conversely, OD stands for Oculus Dexter, the Latin term for the “right eye.” OD and OS typically list distinct values, reflecting the different prescription strengths often needed for each eye. A third term, OU (Oculus Uterque), means “both eyes” and is used when the required vision correction is identical for both eyes.
Understanding the Medical Standard
The consistent use of Latin abbreviations like OS and OD is a medical convention with a long history. Latin was once the universal language of science and medicine, and its legacy remains in various medical fields. Optometry and ophthalmology maintain these terms because they are globally recognized and standardized.
Using a single, traditional set of terms minimizes the risk of transcription errors when eye care professionals communicate prescriptions. While simple English abbreviations like R and L might seem easier, they could be misinterpreted depending on the country or language spoken. The established Latin terms ensure that a prescription written anywhere in the world is interpreted identically by the optician or lab creating the lenses.
Practical Application: Reading Your Eye Prescription
On a typical standardized prescription form, the information is usually organized in a grid format. The convention is to list the measurements for the right eye (OD) first, followed by the left eye (OS). This order is often presented as if the eye care professional is facing the patient, meaning the right eye is on the left side of the chart.
Beneath the OD and OS headings, you will find columns detailing the specific corrective powers. The Sphere (SPH) value indicates the main lens power required for correcting nearsightedness or farsightedness. If you have astigmatism, you will also see values under Cylinder (CYL) and Axis. The OS and OD terms serve to precisely assign these specific SPH, CYL, and Axis measurements to the correct lens, ensuring the resulting eyeglasses accurately address the unique visual requirements of each eye.