What Do “OD” and “OS” Mean on an Eye Prescription?

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“OD” stands for the Latin term “ocular dexter” and means right eye, while “OS” stands for “ocular sinister” and means left eye, according to All About Vision. These terms are traditionally used on eyeglass and contact lens prescriptions though many eye doctors have begun to modernize this practice, opting for “RE” and “LE” to signify right eye and left eye.

All eyeglass and contact lens prescriptions have the right eye listed first and the left eye listed second, according to All About Vision. This is because when an eye doctor faces a patient, he views the right eye first on the left side of the face and the left eye second on the right side of the face. By always writing the prescription in this way, mistakes are avoided. Some prescriptions also have the additional column “OU,” which stands for “oculus uterque” and means both eyes.

Other common terms on an eyeglass prescription include sphere, cylinder, axis, add and prism, according to All About Vision. Together all these terms make up the individual prescription for each eye based on its needs to see clearly. An eyeglass and contact lens prescription are not interchangeable as different criteria are needed regarding the measurement of the eye for a contact lens prescription.