In an eyeglasses prescription, "CYL" stands for Cylinder and indicates the amount of lens power needed to correct astigmatism. A "normal" CYL value typically falls between +/-0.25 to +/-4.00.
Understanding CYL in Eye Prescriptions
Astigmatism occurs when the cornea or lens of the eye is not perfectly spherical, causing blurred vision at all distances. The CYL value corrects this imperfection.
Key Points About CYL:
- It's a Measurement of Astigmatism Correction: CYL specifies the lens power required to compensate for the irregular curvature causing astigmatism.
- Can be Positive or Negative: The value may be expressed as a plus (+) or minus (-) number, depending on the type of astigmatism.
- Absence Indicates No Significant Astigmatism: If there's no number in the CYL column, it generally means you have little to no astigmatism requiring correction.
- Range of Values: While a "normal" CYL is generally considered within +/-0.25 to +/-4.00, the actual value varies depending on the individual's specific astigmatism.
- Combined with Axis: The CYL value is always paired with an "Axis" value, which indicates the orientation of the astigmatism.
Example
For instance, a prescription might read:
- OD (Right Eye): Sphere: -1.00, CYL: -0.50, Axis: 180
- OS (Left Eye): Sphere: -1.50, CYL: -0.75, Axis: 090
In this case, both eyes have astigmatism, with the right eye requiring -0.50 correction and the left eye requiring -0.75 correction. Both fall within the "normal" range.
