Eyeglasses prescription may seem complex at first, but once you know what each section means, it becomes more straightforward. Prescriptions include essential abbreviations and numbers, written in a specific format. In this article, we break down the components one by one, so you can read your prescription with ease.
Understanding Eyeglasses Prescription Information
1. OD and OS
These are abbreviations for Latin terms:
OD stands for "oculus dexter" (the right eye)
OS stands for "oculus sinister" (the left eye)
2. Sphere (SPH)
SPH indicates the main part of the prescription. It represents the amount of lens power required to correct nearsightedness (myopia) or farsightedness (hyperopia).
A minus sign (-) indicates nearsightedness
A plus sign (+) indicates farsightedness
The number associated with the sphere (SPH) is measured in diopters (D).
3. Cylinder (CYL)
CYL is the correction for astigmatism.
Astigmatism occurs when the cornea or the eye's lens has an irregular shape, causing hazy or distorted vision.
If there is no astigmatism correction, this part of the prescription will be listed as "SPH" or "DS."
4. Axis
The Axis is a number between 0 and 180 degrees and defines the orientation of the cylinder correction for astigmatism.
It marks the angle at which the astigmatism correction should be placed on the lens.
5. Addition (ADD)
ADD is the additional magnifying power needed for reading or close-up activities in multifocal lenses, such as bifocals or progressive lenses. It is included in the eyeglasses prescription of people with presbyopia.
This value is always a positive number and is measured in diopters (D).
And here is the difference between regular eyeglasses and eyeglasses with multifocal lenses (that need ADD):
6. Prism and Base
Prism correction is an eyeglasses prescription for eye alignment issues.
It is represented by the abbreviation "PR" or "P," followed by a number. The number indicates the amount of prism in prism diopters (pdpt).
When dealing with eye misalignment, prism correction is often prescribed for each eye individually (OD, OS). But it is possible to have prism correction specified for both eyes together (OU).
The base direction (BU, BD, BI, BO) specifies the direction of the prism:
BU (Base Up): The base of the prism is oriented upward. Shifts the image of an object downward in the visual field.
BD (Base Down): The base of the prism is oriented downward. Shifts the image of an object upward in the visual field.
BI (Base In): The base of the prism is oriented inward, toward the nose. Shifts the image of an object toward the center of the visual field.
BO (Base Out): The base of the prism is oriented outward, away from the nose. Shift the image of an object away from the center of the visual field.
Base designations help the optician understand the direction in which the prism should be oriented to correct eye alignment or binocular vision disorders.
If there is nothing written under the Prism and Base on your eyeglasses prescription, that means you don't have an eye misalignment.
7. Pupillary Distance (PD)
PD is the distance between the centers of your pupils, we measure it in millimeters.
Pupillary distance is always included in an eyeglasses prescription. This way, the optical center of the lenses aligns with your pupils for optimal vision.
In most cases, eye doctors write on the prescription as a Single PD. Which is the total distance between the eye's pupils. But in some medical records, they may need to write a Dual PD, which is the distance from the right eye pupil and the left eye pupil respectively to the center of the nose. See the example below:
Examples: How to Read Eyeglasses Prescription?
Example 1
An example of an eyeglasses prescription for a person with astigmatism might contain these values:
OD: -2.50 Sphere, -1.00 Cylinder, 90 Axis OS: -2.00 Sphere, -0.75 Cylinder, 100 Axis Add: +2.25 PD: 63
This example shows the right eye (OD) needs correction for myopia (-2.50 diopters) and astigmatism (-1.00 diopters at 90 degrees axis). While the left eye (OS) needs correction for myopia (-2.00 diopters) and a smaller amount of astigmatism(-1.00 diopters at 100 degrees axis).
The addition value (ADD) is +2.25, indicating the need for reading glasses. The pupillary distance (PD) is 63 mm.
Example 2
An example of an eyeglasses prescription for a person with eye alignment issues might look like this:
OD: -3.00 Sphere, -1.50 Cylinder, 90 Axis, 4 Base Out OS: -3.00 Sphere, -1.50 Cylinder, 90 Axis, 4 Base Out Add: +2.00 PD: 62
In this example, the person has nearsightedness (-3.00 diopters) and astigmatism (-1.50 diopters at 90 degrees axis) in both eyes (OD & OS). But the notable addition is the prism correction (4 Base Out) to address the esotropia (inward eye position).
Base direction (BO) specifies that the base of the prism is oriented away from the nose, to align the eyes.
The addition value (ADD) is +2.00, indicating the need for reading glasses.
The pupillary distance (PD) is 62 mm.
We hope now it's easier for you to read your eyeglasses prescription!
Remember to take care of your eye health and go for routine eye exams at least once a year to renew your prescription. Checked by Atanas Bogoev, MD.