When you first receive your eyeglass prescription, you may feel completely confused. In reality, prescriptions aren't mysterious or difficult to understand—they simply provide a clear record of your vision status. You can grasp some fundamental prescription knowledge, and we'll break it down for you.
SPH (Sphere):
“Sphere” or “SPH” on your prescription indicates the spherical power, revealing whether you are nearsighted or farsighted. A negative number (-) signifies nearsightedness, while a positive number (+) indicates farsightedness. The higher the number, the stronger the corrective power. For example, -3.00 nearsightedness is more severe than -1.50.
CYL (Cylinder) and AXIS:
If you have astigmatism, your prescription will include “Cylinder (CYL)” and “Axis.” Cylinder indicates the strength of the astigmatism, while Axis specifies its direction, ranging from 1° to 180°. These values typically appear together and are essential for accurate correction.
ADD:
“Add” or “Near Add” frequently appears in prescriptions for presbyopia or progressive lenses, indicating the need for additional magnification in the lower portion of the lens to aid near activities like reading. For individuals over 40, ADD values typically range from +0.75 to +3.00 D and are identical for both eyes.
PRISM:
Some prescriptions also include “Prism” to help eyes achieve a more comfortable balance in cases of visual misalignment or strabismus. Prisms are usually accompanied by directional instructions, such as base up or base out.
After understanding the basics, you can read your prescription step by step in the following order:
Step 1: Identify Eye Correspondence
OD denotes the right eye, OS denotes the left eye, and OU denotes both eyes. Each eye has its own set of measurements.
Step 2: Check SPH
The Sphere number indicates whether you are nearsighted or farsighted. A negative sign indicates nearsightedness, while a positive sign indicates farsightedness. Higher values indicate stronger corrective power.
Step 3: Check CYL and Axis
If these fields contain values, you have astigmatism. Cylinder indicates the strength of astigmatism, while Axis specifies its direction. Together, they help align the lens at the correct angle for correction.
Step 4: Note the Add Value
If your prescription includes Add, it means you require additional reading power, typically used for progressive lenses or bifocals.
Step 5: Pay Attention to Prism
A small number of people require prism correction for binocular coordination. The prism's direction and power will be clearly marked on the prescription.
Many people have different prescriptions for their left and right eyes, which is completely normal. There's no need to worry—simply follow your prescription when getting glasses, and your eyes will still enjoy clear vision.
The strength of your prescription isn't a measure of how good your vision is. It only indicates how much correction is needed. The most important thing is to wear lenses that match your prescription, not to pursue “higher” or “lower” numbers.
Occasionally, you may notice prescription numbers appear rounded. This occurs because lenses are typically manufactured in 0.25D increments, making values like -1.75 or +2.00 standardized results.
If your vision changes rapidly, it's advisable to have an eye exam annually to keep your prescription current. This is especially important for children and adolescents, whose prescriptions may shift significantly within short periods.
Visit our How to Read a Prescription to understand prescriptions. You will find that choosing glasses isn't that difficult. Then visit Eydology—your next favorite pair might be waiting for you.
