From Axis to PD: Learn About Your Eyeglass Prescription

Have you ever wondered what all the codes on your eyeglass prescription mean? Think back to your last eye exam. Your doctor examined your vision while asking you which adjustments improved your sight. After the appointment, you received a prescription with the results, which guided your optician to create unique lenses made just for you.

While a Doctor of Optometry may use automated computerized instruments to help estimate your prescription prior to conducting a more detailed refraction, they use their extensive training and experience along with professional judgment to interpret the results. Only then can an accurate prescription be determined and customized to a patient’s visual needs.

It's a good idea to be knowledgeable about your own vision health. Take a closer look and learn what the codes mean on your prescription.

OD

Oculus dexter is the Latin phrase for the parameters of your right eye. Some doctors use the modernized abbreviation of RE for right eye.

OS

Oculus sinister is the Latin phrase for the parameters of your left eye. Some doctors use the modernized abbreviation of LE for left eye.

OU

Oculus uterque is the Latin phrase for both eyes.

SPH

The sphere indicates the amount of lens power you need prescribed to correct nearsightedness or farsightedness. A negative number means you are nearsighted, while a positive number indicates you are farsighted.

CYL and AXIS

These parameters, always measured together, are the amount of lens power you need to correct astigmatism.

ADD

This parameter indicates how much magnifying power you need to correct vision for reading, progressive, and bifocal lenses.

Prism

Prismatic power is measured in prism diopters. This is added to your prescription if you require eye alignment compensation.

PD

Pupillary distance is the space measured in millimetres between the centre of one pupil (the black dot of your eye) to the centre of the opposite pupil.

BC and DIA

The base curve and diameter are the measurements of a contact lens’ fit on the cornea and surface of the eye. Proper fit with these two parameters ensures comfort and encourages oxygen to reach the eye.

Remember, your OD accurately interprets your unique vision prescription using years of training and experience along with automated computerized instruments. To learn more about your personalized glasses or contact lens prescription, talk to your optometrist. You can make an appointment at an FYidoctors location near you today.