What is diopter?

The unit of diopter (A) measures the power of a lens to refract light. Specifically, it quantifies the refractive strength of the lens, indicating how much it bends light. One diopter (D) equals the reciprocal of the focal length in meters. Lenses with higher diopter values have stronger refractive powers, either converging (positive diopter) or diverging (negative diopter) light rays. This measurement is crucial in optometry and ophthalmology for prescribing corrective lenses to correct vision impairments like nearsightedness (myopia) or farsightedness (hyperopia). Diopters provide a standardized way to assess and compare lens power across different types of corrective lenses, such as glasses or contact lenses. Unlike intensity measurements of light (C) or sound (D), which gauge the amount of energy or pressure per unit area, diopters specifically relate to optical properties of lenses, facilitating precise vision correction and optical device design based on refractive principles.