Understanding your eye prescription can seem like decoding a secret message, but it’s actually quite straightforward once you know what the abbreviations and numbers mean. Whether you’ve just had an eye exam or you’re ordering new glasses online, knowing how to read your prescription is essential. In this blog post, we'll break down the key components of your eye prescription and explain what each part means. At the end we will also have a complete glasses prescription example interpretation.
1. The Basics: OD and OS
Your eye prescription typically starts with the abbreviations OD and OS:
These abbreviations are followed by a series of numbers and letters that describe the specific vision correction needed for each eye.
2. SPH (Sphere)
The SPH (Sphere) value indicates the lens power needed to correct your vision. It is measured in diopters and can be either positive or negative:
Negative numbers (-): Indicate nearsightedness (myopia), meaning you can see close objects clearly but have difficulty seeing things at a distance.
Positive numbers (+): Indicate farsightedness (hyperopia), meaning you can see distant objects clearly but may struggle with close-up tasks.
The SPH value represents the degree of correction required. For example, a SPH of -2.00 means you have mild myopia, while +4.00 indicates moderate hyperopia.
3. CYL (Cylinder) and AXIS
If you have astigmatism, your prescription will include a CYL (Cylinder) value and an AXIS:
CYL: Measures the degree of astigmatism, which is a condition where the cornea or lens is irregularly shaped, causing blurred or distorted vision. The CYL value indicates how much correction is needed.
AXIS: Refers to the orientation of the astigmatism, measured in degrees from 0 to 180. The axis specifies the direction in which the lens should correct the astigmatism.
For example, a prescription might say CYL -1.25, AXIS 90. This means there is a mild astigmatism that needs correction, and the lens must be aligned along the 90-degree meridian.
4. ADD (Addition)
The ADD value is found on prescriptions for bifocals, trifocals, or progressive lenses. It indicates the additional magnifying power needed for close-up tasks, such as reading. The ADD value is usually the same for both eyes and is a positive number.
For example, ADD +2.00 means an extra 2 diopters of magnification are needed for near vision.
5. PRISM and Base
Sometimes, your prescription may include a PRISM value. This is used to correct issues with eye alignment, such as double vision. The prism is measured in prism diopters, and it helps to align the images seen by both eyes.
The Base direction specifies the orientation of the prism, indicating whether the prism is ground in the direction of the base (up, down, in, or out)：
BU – Base up (the base is at the top of the lens)
BD – Base down (the base is at the bottom of the lens)
BI – Base in (the base is on the inner side of the lens)
BO – Base out (the base is on the outer side of the lens)
6. PD (Pupillary Distance)
While not always included on the prescription itself, PD (Pupillary Distance) is crucial for ordering glasses. It measures the distance between the centers of your pupils in millimeters. This measurement ensures that your lenses are correctly aligned with your eyes.
A typical PD might range from 54mm to 68mm for adults.
7. Example of an Eye Prescription
Here’s a sample prescription to bring it all together:
This prescription shows that the person has mild hyperopia with a SPH of +0.25 diopters in the right eye and moderate hyperopia with a SPH of +1.50 diopters in the left eye. Both eyes have astigmatism, with a CYL of -1.75 diopters in the right eye and -1.25 diopters in the left, each aligned along the 148-degree axis. Additionally, the person requires prism corrections: 1 diopter with the base outward (BO) for the right eye, and 2 diopters with the base inward (BI) for the left eye.
Can eyeglass prescriptions be used to buy contact lenses?
No, eyeglass prescriptions cannot be used to buy contact lenses. This is because contact lenses require different measurements and specifications, such as the base curve and diameter, which are not included in eyeglass prescriptions. Additionally, the lens power may differ due to the way contact lenses sit directly on the eye, unlike glasses. Therefore, a separate contact lens prescription is necessary, which you'll get after a fitting with your eye care professional.
Your Right to an Eyeglass Prescription Copy
Get Your Eyeglass Prescription—No Strings AttachedThe Federal Trade Commission (FTC), which is the U.S. government's consumer protection agency, enforces the Prescription Release Rule. This rule mandates that eye doctors provide patients with a copy of their eyeglass prescription at the end of an eye exam that includes a refraction.
The rule is designed to make your prescription "portable," allowing you the flexibility to purchase glasses from any vendor you prefer.
Your eye doctor is required to give you a copy of your prescription automatically, whether you request it or not. They cannot make the release of your prescription conditional on you buying glasses from them, nor can they charge you an additional fee to release it.
