Understanding your eye exam results is crucial for managing your vision. Let's break down the key components typically found on a prescription.
Understanding the Basics
An eye exam prescription primarily uses numbers to indicate the amount of lens power needed to correct your vision. These numbers are measured in diopters. The diopter value indicates the lens strength necessary to correct focusing errors like nearsightedness or farsightedness.
Sphere (SPH)
The sphere value corrects nearsightedness or farsightedness:
- Minus (-) sign: Indicates nearsightedness. For instance, a prescription of -1.00 means your eyeglasses need 1 diopter of strength to correct nearsightedness. According to the reference, the higher the number the more correction needed.
- Plus (+) sign: Indicates farsightedness. For example, a prescription of +2.50 means your eyeglasses need 2.5 diopters of strength to correct farsightedness. The higher the number, the more correction your vision needs, just like with nearsightedness.
Cylinder (CYL) & Axis
- Cylinder (CYL): This value addresses astigmatism, a condition where the cornea isn't perfectly round.
- This number, usually negative, tells the lens power needed to correct astigmatism.
- Axis: The axis indicates the orientation of the astigmatism correction and is always a value between 1 and 180.
Add (ADD)
- This indicates the additional magnifying power needed for reading for people with presbyopia.
- It is used in bifocal, trifocal or progressive lenses
Prism
- Prism: This value is used when there is a need to correct eye alignment issues.
- This number is often small, and a direction indicated for the way the prism should be applied.
Deciphering a Sample Prescription
Let's consider an example:
| Component | Right Eye (OD) | Left Eye (OS) |
|---|---|---|
| Sphere (SPH) | -2.00 | -1.50 |
| Cylinder (CYL) | -0.50 | -0.75 |
| Axis | 180 | 90 |
| ADD | +1.25 | +1.25 |
In this example:
- Right Eye (OD): This eye requires a -2.00 diopter sphere correction for nearsightedness, along with a -0.50 cylinder correction at an axis of 180 for astigmatism.
- Left Eye (OS): This eye requires a -1.50 diopter sphere correction for nearsightedness, along with a -0.75 cylinder correction at an axis of 90 for astigmatism.
- ADD: Both eyes need an additional +1.25 power for reading (presbyopia correction).
Key Takeaways
- A minus (-) sign in the sphere (SPH) indicates nearsightedness.
- A plus (+) sign in the sphere (SPH) indicates farsightedness.
- The higher the number, the more correction needed.
- Cylinder (CYL) and Axis correct astigmatism.
- ADD corrects reading difficulties from presbyopia.
Understanding your prescription empowers you to make informed decisions regarding your vision care. If you're unsure about any aspect of your prescription, always consult your eye care professional.
