A "power contact lens" refers to a contact lens that corrects refractive errors (like nearsightedness, farsightedness, and astigmatism) by having a specific optical power, usually measured in diopters (D). Essentially, "power" indicates the strength of the lens needed to provide clear vision.
Understanding "Power" in Contact Lens Prescriptions
The term "power" (PWR) on a contact lens prescription is interchangeable with "spherical correction" (SPH). Both terms denote the lens's ability to bend light and focus it correctly onto the retina.
- Positive Power (+): Used to correct farsightedness (hyperopia). These lenses converge light rays before they enter the eye.
- Negative Power (-): Used to correct nearsightedness (myopia). These lenses diverge light rays before they enter the eye.
Components of a Contact Lens Prescription
Besides the power (PWR or SPH), a contact lens prescription includes other essential parameters:
- Base Curve (BC): Specifies the curvature of the back surface of the lens, ensuring a proper fit on the cornea.
- Diameter (DIA): Indicates the overall size of the lens in millimeters.
- Cylinder (CYL) & Axis: Used to correct astigmatism. CYL indicates the amount of astigmatism, and Axis specifies the orientation of the astigmatism.
- Add Power: Used in multifocal or bifocal contact lenses to correct presbyopia (age-related loss of near vision).
- Lens Brand/Material: Specifies the brand and material of the contact lens.
Example
A contact lens prescription might look like this:
| Parameter | Value |
|---|---|
| PWR (SPH) | -3.00 D |
| BC | 8.5 |
| DIA | 14.2 |
This prescription indicates a contact lens with a power of -3.00 diopters to correct nearsightedness, a base curve of 8.5 mm, and a diameter of 14.2 mm. Other values may be present depending on the individual's specific needs.
In summary, the "power" of a contact lens refers to its strength, measured in diopters, which is required to correct refractive errors and provide clear vision. It is an essential component of a contact lens prescription.
