Have you ever received your prescription at the end of your exam but were unsure how to interpret it? Below are some common questions and terms explained to help you better understand what each part of your prescription means. If you have any questions about your prescription, please reach out to our office.
What does it mean to be nearsighted?
Nearsightedness (myopia) is the most commonly diagnosed refractive error. Nearsighted individuals have difficulty reading road signs and clearly seeing distant objects. This refractive error typically begins in childhood and stabilizes in early adulthood. Symptoms of myopia include squinting, eye strain, and headaches.
What does it mean to be farsighted?
Farsightedness (hyperopia) affects about one-fourth of the population.* Farsighted individuals will have difficulty focusing on objects up close but can clearly see objects at a distance. The eye shape of someone who is farsighted is shorter than normal. For this reason, many children are born farsighted and outgrow it as their eyeball grows.
I have astigmatism, what does that mean?
Individuals with astigmatism usually experience some degree of blur or distortion at all distances. In astigmatism, light comes into the retina at multiple focus points because of an irregular shaped cornea, which causes blurring. With astigmatism, one or both eyes can be farsighted, one or both eyes can be nearsighted, or one eye can be nearsighted while the other is farsighted.
Reading the Prescription
Your prescription is an outline of corrections your eyes need in order to see as precisely as possible. Every prescription will look different based on the patient’s eyes. If you have questions or do not understand a section of your exam or prescription, be sure to ask your doctor.
OD and OS
Doctors use the abbreviations OD, OS, and OU when writing a prescription for eyeglasses, contact lenses, and eye medicines. OD and OS are abbreviations for the latin words oculus dexter (right eye) and oculus sinister (left eye). The latin term oculus uterque is used for describing both eyes.
Other terms on your prescription:
- Sphere (SPH): Indicates the lens power needed to correct nearsightedness or farsightedness. If you have a minus sign (-) you are nearsighted; if you have a plus sign (+) or no sign you are farsighted.
- Cylinder (CYL): Indicates the amount of lens power for astigmatism. If nothing appears in this column you do not have astigmatism. The minus sign is for nearsighted astigmatism and a plus sign for farsighted astigmatism.
- Axis: Indicates the direction of astigmatism. For example, if the axis is 180 degrees the astigmatism is horizontal.
- Add: Indicates the magnifying power applied to the bottom of multifocal lenses to correct presbyopia. The number is typically a plus power and will be the same for both eyes.
- Prism: This is to compensate for eye alignment problems, a very small percentage of prescriptions contain a prismatic power. Abbreviations used for prism direction: BU- base up, BD- base down, BI- base in, BO- base out.
*All About Vision