An eye prescription contains abbreviations and symbols used by eye care practitioners to communicate precise measurements and instructions. Deciphering these terms, which include OD, OS, and OU, is the first step toward understanding the corrective measures prescribed for your vision. This article clarifies the meaning of these common optical terms to help you interpret your vision records.
The Meaning of OD and OS
The abbreviation OD stands for Oculus Dexter, which designates the right eye. Conversely, OS is the abbreviation for Oculus Sinister, referring to the left eye.
The distinction between these two eyes is maintained because vision correction is frequently asymmetrical. It is common for one eye to require a slightly different lens power than the other to achieve optimal clarity. Using these precise abbreviations ensures the laboratory places the correct power into the frame for each eye, preventing potentially harmful errors.
Understanding OU and the Latin Foundation
Beyond the individual eye designations, you may encounter the abbreviation OU, which stands for Oculus Uterque. This term refers to both eyes together. The OU designation is employed when a vision measurement or treatment instruction applies equally to the right and left eyes.
The continued use of these terms stems from the long-standing tradition of using Latin in medical notation. The foundational word, “Oculus,” is the Latin term for eye, forming the root of all three abbreviations. Historically, Latin was the universal language among scholars and scientists, providing a standardized terminology across different countries and medical disciplines.
Where This Terminology Appears on Your Prescription
On a typical eyeglass prescription form, the terms OD and OS serve as row headings in a table format that organizes the numerical measurements. By convention, the data for the right eye (OD) is always listed first, occupying the top row. The information for the left eye (OS) is then listed immediately below it, comprising the second row of the chart.
This standardized layout ensures that the various measurements, such as sphere, cylinder, and axis, are precisely matched to the correct eye. The OU designation is not typically used for the primary distance or reading power but may appear in the “Add” column. The “Add” power, which represents the magnifying power needed for reading, is often the same for both eyes, and the OU label indicates that the additional power is symmetrical. This structured presentation eliminates ambiguity.