When you read your eyeglasses prescription, all you may see is a series of strange numbers and letters. While it looks mysterious, each of those notations has a specific meaning. By understanding what your eyeglasses prescription says, you can learn more about the current state of your vision and the corrections your optometrist or ophthalmologist ordered. If you want to read yours properly, here’s what you need to know.
OS, OD, and OU
OS, OD, and OU are Latin abbreviations that identify which eye your doctor is referring to on the prescription. OS stands for oculus sinister, which means your left eye. OD is oculus dextrus, which refers to your right eye.
If you see OU, which stands for oculus uterque, that is a reference to both of your eyes. OU isn’t always present on an eyeglasses prescription, as not all patients have points that apply to both of their eyes.
Nearsightedness and Farsightedness
Near the OS and OD headings, you’ll usually see numbers and plus (+) or minus (-) signs. They may be in a column labeled “sphere” or “S.” These describe your prescription’s strength.
The number represents diopters (which may be abbreviated as “D”), a unit of measurement that correlates to the amount of correction that is necessary. 1.00 stands for one diopter. However, the correction can be measured in one-quarter diopters. For example, 1.25 is one and one-quarter diopters.
Typically, the further away from zero, the stronger the prescription. For example, 3.50 means that more correction is needed in comparison to a 2.25.
The plus and minus let you know if you are near or farsighted. When a plus sign is in front of the number, that means you are farsighted. In farsighted individuals, objects closer to your eyes are typically blurry, but further away objects are clear.
When there is a minus sign in front of the number, that means you are nearsighted. Typically, objects close to your eyes seem clear, and those that are far away appear blurry.
If your prescription reads -2.00, that means you are two diopters nearsighted. If your prescription said +3.50, you are three and a half diopters farsighted.
Astigmatism
If you have astigmatism – a condition that can be caused by an irregularly shaped cornea or a lens curvature – you may see some additional numbers. Usually, the numbers are written in an S x C x Axis format.
The S is the “spherical” part of the prescription, usually noting the degree of nearsightedness or farsightedness as described above. The C, or “cylinder,” actually represents the astigmatism. It is also measured in diopters and can be positive or negative.
The Axis is a number that can be anywhere between 0 and 180 degrees. It describes how the astigmatism is oriented, noting the nature and direction of the curvature. This ensures that any astigmatism corrections in your glasses are positioned in the right way to make the needed correction.
If you have astigmatism, here is an example of what that prescription might look like for one eye:
-2.25 +1.00 x 45
That example means the patient has 2.25 diopters of nearsightedness, 1 diopter of astigmatism, and an axis of 45 degrees.
Add and Prism
Your glasses prescription may also have numbers in the “Add” and “Prism” columns, but they may not. “Add” is used when a patient needs multifocal lenses and notes how much power needs to be added to the lower portion of the lens. This allows the lower part to offer stronger magnification, making it easier for glasses wearers to read or do other up-close work.
The “Prism” section indicates prismatic power. If there are eye alignment issues, a prism may be used to correct the problem. It is measured in prism diopters (p.d.) and is commonly accompanied by a notation for the prisms position (or base) in the lens, such as up (BU), down (BD), toward the wearer’s nose (BI or base in), or toward the glasses wearer’s ear (BO or base-out).
After reviewing the information above, you should be able to understand your eyeglasses prescription. If you haven’t had your vision checked recently, schedule an appointment at your nearest ECVA clinic today. Our skilled ophthalmologists, optometrists, and opticians work diligently by performing thorough exams, allowing vision issues to be corrected and ensuring eye health.
TALK WITH ONE OF OUR EYE CARE PROFESSIONALS TODAY!
If you have further questions or would like to schedule an appointment with one of the Ophthalmologists at Eye Care and Vision Associates please call 716.631-EYES (3937) or visit www.ecvaeyecare.com .
