Cylinder, Axis, Spherical and B.C. Explained in Contact Lenses
Contact Lenses Prescription Parameters
When looking at your contact lens prescription, you might see terms like Cylinder (CYL), Axis, and Spherical (SPH). These measurements are crucial for ensuring that your contact lenses correct your vision effectively.
Spherical (SPH): This indicates the main strength of your contact lenses, correcting nearsightedness (myopia) or farsightedness (hyperopia). The value is measured in diopters (D), with a negative value indicating nearsightedness and a positive value indicating farsightedness.
Cylinder (CYL): The cylinder value is used to correct astigmatism. It represents the degree of astigmatism correction needed and is also measured in diopters. This value indicates how much extra power is needed to correct the irregular curvature of the cornea.
Axis: The axis value is used in conjunction with the cylinder value to determine the orientation of astigmatism correction. The axis is measured in degrees (from 0 to 180) and indicates the direction of the cylindrical power needed to correct the astigmatism. It helps to align the toric lens properly on the eye to ensure the best vision correction.
Base Curve (BC):Â Refers to the curvature of the inner surface of a contact lens. It is measured in millimeters (mm) and indicates how well the lens fits the curvature of your cornea.
| Parameter | Abbreviation | Full Name | Description |
|---|---|---|---|
| Power | SPH | Sphere | Corrects nearsightedness (−) or farsightedness (+) |
| Astigmatism Power | CYL | Cylinder | Corrects astigmatism |
| Astigmatism Axis | Axis | Axis | Indicates the orientation of astigmatism (0°–180°) |
| Base Curve | BC | Base Curve | Determines the curvature of the lens for fit and comfort |
| Diameter | DIA | Diameter | Overall size of the contact lens |
| Lens Curvature | Curve | Curve / Base Curve | Same as BC, sometimes labeled differently |
Understanding these parameters is essential for getting the right fit for your Contact Lenses and achieving the best visual outcomes.Â