The diopter is the unit of measurement used in optics. It determines the measurement capabilities of refraction, the changes in the path of light rays as they pass through a natural environment such as the eye or an artificial one such as glasses or contact lenses. This unit allows the calculation of the degree of correction for lenses used for nearsightedness or farsightedness. The higher the diopter, the higher the degree of correction. To correct myopia, diverging lenses are used and their diopter is negative. This is the reverse of hyperopia with converging lenses and a positive diopter measurement.