Contact lens prescriptions contain a series of numbers and abbreviations that dictate the lens specifications. One value that often causes confusion is the presence of “0.00” in the prescription’s power section. This number indicates a lack of refractive correction. This article clarifies what this measurement means and examines the other crucial specifications that apply to every contact lens.
Understanding the “0.00” Measurement
The “0.00” found on a contact lens prescription specifically refers to the Sphere (SPH) or Power measurement, which is the optical strength of the lens. This value is measured in diopters, a unit describing the lens’s convergence or divergence power needed to focus light onto the retina. A negative number, such as -2.50, corrects nearsightedness (myopia), while a positive number, like +1.75, corrects farsightedness (hyperopia).
When the prescription lists 0.00 or the abbreviation “PL” for Plano in the SPH column, it signifies zero refractive power. This means the lens will neither converge nor diverge light and is not intended to correct vision. Individuals who have 20/20 vision or better and do not have a refractive error typically receive this specific power measurement.
The term Plano originates from the Latin word for “flat,” denoting a lens surface with no curvature designed to alter the path of light. The 0.00 diopter value confirms that the wearer does not require correction for common vision issues. Even though the power is zero, the lens is still a precisely manufactured medical device.
The use of this exact measurement is important because even minor deviations from zero power, such as 0.25 diopters, can affect visual clarity for someone who does not need correction. This value ensures that the eye’s natural focusing ability is preserved while the lens is being worn.
Essential Contact Lens Measurements Beyond Power
While the power measurement is the most recognized part of a prescription, other values are necessary to ensure the lens fits the eye safely and comfortably. The Base Curve (BC) is a fundamental measurement, typically written in millimeters, that determines how the lens rests on the cornea’s curvature. This value must match the natural curve of the eye to prevent the lens from being too tight or too loose.
A tight lens restricts the flow of tears and oxygen, potentially leading to corneal swelling or irritation. A loose lens can shift excessively with each blink, causing discomfort and unstable vision. The Base Curve is a non-negotiable measurement for any contact lens, including those with 0.00 power, and is often offered in a limited range (e.g., 8.4 to 9.0 millimeters).
The Diameter (DIA), also measured in millimeters, dictates the overall size of the lens from edge to edge. This measurement ensures the lens properly covers the cornea and sits correctly on the sclera (the white part of the eye). Together, the Base Curve and Diameter ensure the specific contact lens is compatible with the person’s unique eye shape.
If a person has astigmatism, two additional measurements, Cylinder (CYL) and Axis (AXIS), will be present, even if the SPH power is 0.00. The Cylinder value specifies the extra power needed to correct the astigmatism. The Axis, measured in degrees from 0 to 180, indicates the orientation of that correction on the eye.
Reasons for Wearing Plano Lenses
Contact lenses with a 0.00 power, often called Plano lenses, serve various purposes beyond vision correction. The most common application is purely cosmetic, allowing a person to temporarily change or enhance their natural eye color. These color contacts are designed with a clear central zone so the wearer’s natural vision remains unaffected by the colored portion of the lens.
Plano lenses are also used for novelty or costume purposes, featuring unique designs for theatrical or holiday events. Additionally, some non-corrective lenses are used therapeutically, such as clear, zero-power bandage contact lenses. These protective lenses are placed over the cornea to act as a smooth, temporary barrier during healing from injury or surgery.
Even though these lenses do not correct vision, they are classified as medical devices by regulatory bodies. Therefore, a comprehensive eye examination and a valid prescription are still required to purchase any contact lens, including those with 0.00 power. The prescription ensures the Base Curve and Diameter are correct, protecting against potential issues like corneal abrasion or infection from a poorly fitting lens.