Vertex distance is a measurement of how far a corrective lens is placed from the eye, and if it differs from the distance the doctor used during the eye exam, it may have an impact on the patient's effective power of correction.
Light is distorted, or refracted, as it travels from one medium (like air) into another that is denser (like water).
Whether a patient is myopic or hyperopic is determined by the prescription's sphere power. Myopia is shown by minus numbers, while hyperopia is indicated by positive values.
The ability to bend a coherent beam of light by 1 centimeter at a distance of 1 meter from the lens is known as the diopter, which serves as the fundamental unit of measurement for refractive power.
A plus-power lens is designed such that light rays travelling through it will converge into a single point.
Although the UV spectrum starts at about 400 nanometers, the skin is most severely harmed by wavelengths below 320 nm. Fortunately, the Earth's atmosphere largely absorbs wavelengths shorter than 290 nm.
The distance from the lens's center to the place where the light rays condense into a single point, or focus, is known as the focal length.