An eye prescription is a detailed record of your vision correction needs, provided after an eye exam by an optometrist or ophthalmologist. Whether you need glasses or contact lenses, understanding your prescription is essential for choosing the right eyewear. While it may seem like a confusing set of numbers and abbreviations, each element has a specific meaning related to your eyesight.
Breaking Down an Eye Prescription
A typical eye prescription includes several values, each representing different aspects of your vision General correction needs. Here’s what they mean:
1. OD and OS (Right and Left Eye)
- OD (Oculus Dexter) – Refers to the right eye.
- OS (Oculus Sinister) – Refers to the left eye.
- Some prescriptions also include OU (Oculus Uterque), meaning both eyes.
2. Sphere (SPH) – Nearsightedness or Farsightedness
The sphere (SPH) value indicates the degree of nearsightedness (-) or farsightedness (+).
- A negative (-) number means you are nearsighted (myopia) and have difficulty seeing distant objects clearly.
- A positive (+) number means you are farsighted (hyperopia) and struggle with close-up vision.
- The higher the number, the stronger the prescription needed.
3. Cylinder (CYL) and Axis – Astigmatism Correction
If you have astigmatism, your eye prescription will include cylinder (CYL) and axis values:
- Cylinder (CYL): Measures the degree of astigmatism, or how irregularly shaped your cornea is. A higher CYL value means more correction is needed.
- Axis: A number between 1° and 180°, indicating the orientation of astigmatism correction.
If your prescription does not include a CYL or axis, it means you do not have astigmatism or that it is very mild.
4. Add (Addition) – Presbyopia Correction
For people over 40, the ADD value is included in prescriptions for bifocal or progressive lenses to correct presbyopia (age-related near vision loss). It is always a positive number (e.g., +1.25, +2.00).
5. Prism and Base – Eye Alignment Correction
- Prism: Used for patients with double vision (diplopia) to help align the eyes properly.
- Base: Indicates the prism’s direction (up, down, in, or out).
6. Pupillary Distance (PD)
- The PD (Pupillary Distance) measures the distance (in millimeters) between the centers of your pupils.
- PD ensures that glasses lenses are correctly centered for proper vision correction.
Reading an Example Eye Prescription
OD (Right Eye) | OS (Left Eye) | SPH | CYL | Axis | ADD | PD |
---|---|---|---|---|---|---|
-2.50 | -3.00 | -2.50 | -1.00 | 180° | +2.00 | 63mm |
- This person has nearsightedness (-2.50 and -3.00).
- They also have astigmatism (-1.00 in the left eye, with an axis at 180°).
- They need progressive or bifocal lenses (+2.00 ADD) for reading vision.
- Their PD is 63mm, ensuring proper lens alignment.
Understanding your eye prescription helps you make informed decisions about glasses or contact lenses. If you’re unsure about any part of your prescription, ask your optometrist or ophthalmologist for clarification. Regular eye exams ensure your vision remains clear and your prescription stays up to date.